Journal of Colloid And Interface Science (v.299, #2)
Editorial Board (CO1).
Adsorption of Cu(II) and Ni(II) on solid humic acid from the Azraq area, Jordan by Bassam El-Eswed; Fawwaz Khalili (497-503).
Isotherms of adsorption of Cu(II) and Ni(II) onto solid Azraq humic acid (AZHA) were studied at different pH (2.0–3.7) values and 0.1 M NaClO4 ionic strength. The Langmuir monolayer adsorption capacity was found to range from 0.1 to 1.0 mmol metal ion/g AZHA, where Cu(II) has higher adsorptivity than Ni(II). The previously reported NICA–Donnan parameters for sorption of Cu(II) on HA fit the amount of Cu(bound) determined in the present study at pH 3.7 but underestimates those at pH values of 3.0, 2.4, and 2.0. The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may increase the ability of low-affinity sites to encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II). AZHA loaded with Cu(II) and Ni(II) was found to be insoluble in water with no measurable amount of desorbed metal ions.The contribution of low affinity sites to binding of metal ions increases with decreasing pH and increasing metal ion loading. The aggregation of HA, which is facilitated by decreasing pH and increasing metal loading, may create new sites that can encapsulate metal ions. The binding of Ni(II) to HA exhibits less heterogeneity and less multidentism than that of Cu(II).
Keywords: Azraq humic acid; Solid humic acid; Adsorption; Cu(II) and Ni(II) metal ions; NICA–Donnan;
Reflectometric study of the adsorption of poly(vinyl imidazole) on a gold electrode, effects of pH, and applied potential by T. Roques-Carmes; F. Membrey; M. Kaisheva; C. Filiâtre; A. Foissy (504-512).
The adsorption–desorption behavior of poly(vinyl imidazole), a weak polybase (pH-dependent positive charge), on a gold electrode was investigated using optical fixed-angle reflectometry. Using an instrument comprising an impinging-jet system, the hydrodynamic conditions were well defined, making it possible to study the adsorption rate. Comparison between the actual adsorption rate and that of a purely diffusion-controlled process revealed the occurrence and the change of an electrostatic barrier in the adsorption process. The surface charge of the gold electrode was varied by means of an externally applied potential. The surface charge density was evaluated by separate electrochemical impedance spectroscopy. The uptake and the adsorption rate were very sensitive to pH and electrode polarization. At pH 3, the adsorption of the fully charged polymer increased fairly regularly with cathodic polarization, whereas it remained at about 0.4 mg m−2 in the anodic zone At pH 8, the adsorption of the uncharged polymer decreased with the negative charge of the electrode due to the more favorable adsorption of potassium ions on the charged electrode. Discrepancies in adsorption–desorption measurements taken while cycling the pH were due to an electrostatic adsorption barrier.Reflectometric output, consecutive to the adsorption of poly(vinyl imidazole) on gold as a function of electrode potential. Solution PVI 0.1 g L−1, KNO3 10 −2 M , pH 8.
Keywords: Polyelectrolyte adsorption; Poly(vinyl imidazole); Gold electrode; Adsorption rate; Electrostatic barrier; Reflectometry; Electrochemical impedance spectroscopy;
Adsorption characteristics of bisphenol-A in aqueous solutions onto hydrophobic zeolite by Wen-Tien Tsai; Hsin-Chieh Hsu; Ting-Yi Su; Keng-Yu Lin; Chien-Ming Lin (513-519).
The adsorption behavior of bisphenol-A, which is a hydrophobic organic compound and also listed as one of endocrine disrupting chemicals, from aqueous solution onto hydrophobic zeolite at 25 °C have been studied using a batch adsorption process in terms of a pseudo-second-order equation and three common isotherms (i.e., the Langmuir, Freundlich, and Redlich–Peterson). The pore properties of the Y-type zeolite have been determined using N2 adsorption–desorption isotherms, indicating that it is a supermicroporous adsorbent associated with a lower percentage of mesopores. Based on the kinetic model the effects of particle size, initial bisphenol-A concentration, initial solution pH, and adsorbent dosage on the adsorption rate constant and equilibrium capacity have been estimated, showing that the adsorption process could be simulated well by the simplified kinetic model. From the data on the equilibrium adsorption capacities obtained by fitting the pseudo-second-order model, the adsorption isotherm could be better described by the three-parameter Redlich–Peterson model than by the two-parameter models (i.e., the Langmuir and Freundlich).
Keywords: Bisphenol-A; Liquid-phase adsorption; Hydrophobic zeolite; Kinetic modeling; Isotherm;
The ionic strength effect on microcystin and natural organic matter surrogate adsorption onto PAC by Margarida Campinas; Maria João Rosa (520-529).
This work aims to contribute to a better understanding of the ionic strength effect on microcystin and natural organic matter (NOM) surrogate adsorption by analyzing the importance of adsorbate molecular size, and surface concentration. Adsorption kinetics and/or isotherms were performed on PAC Norit SA-UF for four microcystin variants (MC-LR, MC-LY, MC-LW, MC-LF), and three NOM surrogates (salicylic acid (SA), tannic acid (TA), Aldrich humic acid (AHA)) at different solution ionic strengths. Results showed that the ionic strength effect depends upon the adsorbate surface concentration, cation charge (mono or divalent), and adsorbate molecular size. Potassium seemed not to affect the MC-LR adsorption, while calcium enhanced MC-LR kinetics and adsorption capacity. K+ and, particularly, Ca2+ improved the adsorption kinetics of the other microcystin variants. For identical surface concentration and ionic strength, the impact of K+ and Ca2+ on NOM surrogates depended on the adsorbate molecular size: K+ effect was only observed for AHA, whereas Ca2+ caused no effect on SA adsorption, slightly enhanced TA adsorption, and greatly enhanced AHA adsorption. MC-LR isotherms with two salt concentrations (KCl or CaCl2) indicated that, for the studied range of equilibrium surface concentration (5.3–18.7 mg/g), an enhanced adsorption regime prevails, and no transition regime was observed.
Keywords: Microcystins; PAC; Adsorption; NOM surrogates; Surface concentration; Ionic strength;
Adsorption of chromium ions from aqueous solution by using activated carbo-aluminosilicate material from oil shale by Reyad Awwad Shawabkeh (530-536).
A novel activated carbo-aluminosilicate material was prepared from oil shale by chemical activation. The chemicals used in the activation process were 95 wt% sulfuric and 5 wt% nitric acids. The produced material combines the sorption properties and the mechanical strength of both activated carbon and zeolite. An X-ray diffraction analysis shows the formation of zeolite Y, Na-X, and A-types, sodalite, sodium silicate, mullite, and cancrinite. FT-IR spectrum shows the presence of carboxylic, phenolic, and lactonic groups on the surface of this material. The zero point of charge estimated at different mass to solution ratio ranged from 7.9 to 8.3. Chromium removal by this material showed sorption capacity of 92 mg/g.A new activated carbo-aluminosilicate material was prepared from oil shale, and characterized according to its surface morphology, functional groups and mineral content. It was used as an adsorbent for removal of chromium ions from aqueous solution.
Keywords: Activated carbo-aluminosilicate; Adsorption; Sulfuric and nitric acids; FT-IR; XRD; Chromium;
Adsorption of heavy metals on vermiculite: Influence of pH and organic ligands by M. Malandrino; O. Abollino; A. Giacomino; M. Aceto; E. Mentasti (537-546).
The sorption behaviour of vermiculite has been studied with respect to cadmium, copper, lead, manganese, nickel, and zinc as a function of pH and in the presence of different ligands. The continuous column method was used in order to evaluate the feasibility to use the clay in wastewater purification systems. The total capacity of vermiculite was found to decrease in the following order: Mn > Ni > Zn > Cd > Cu > Pb. The adsorption of metal ions on vermiculite decreases with decreasing pH and increasing ionic strength. In general, the metal uptake on the clay was hindered by the presence of strong complexing agents in solution and it decreases with increasing of the complexation constants of the ligands with exception of cysteine and tiron. It is necessary, hence, to consider all these factors to effectively predict the uptake efficiency of this sorbent. However, it is possible to conclude that the vermiculite has good potentialities for cost-effective treatments of metal-contaminated wastewaters.The uptake of metals on vermiculite in presence of organic ligands depends on the charge of the complexes and is consistent with the order of their stability constants.
Keywords: Vermiculite; Heavy metals; Wastewaters; Adsorption; Metal complexes; Breakthrough;
Spectroscopic investigation of the adsorption mechanisms of polyacrylamide polymers onto iron oxide particles by Melanie J. McGuire; Jonas Addai-Mensah; Kristen E. Bremmell (547-555).
The mechanisms of high-molecular-weight polyacrylamide nonionic homopolymer and 25 mol% anionic acrylate-substituted copolymer adsorption onto iron oxide particles were investigated via DRIFT and UV–vis spectroscopies at three pH values (6, 8.5, and 11). While electrostatic interactions play an important role in charged polymer adsorption, this information is not spectroscopically available. At pH values above and below pH 8.5 (the isoelectric point for the anionic polymer), bidentate chelation and hydrogen bonding were the main adsorption mechanisms. At the isoelectric point, monodentate chelation was observed to be the main mode of adsorption, along with hydrogen bonding. For the nonionic polymer, in all cases, hydrogen bonding through the carbonyl group was the main mode of adsorption. The adsorption of both polymers conformed well to the Freundlich model, suggesting that the adsorbed polymer amount increases with increasing polymer concentration up to 7500 g/t solid, rather than approaching monolayer coverage. Spectroscopic evidence was found to suggest that hydrolysis of nonionic polyacrylamide occurs at high pH.Adsorption mechanisms of polyacrylamide-based polymers onto iron oxide determined by infrared spectroscopy.
Keywords: Polymer adsorption; Polyacrylamide; Hematite; Adsorption mechanism; Hydrolysis; Infrared spectroscopy;
Adsorption of 2,4-D and carbofuran pesticides using fertilizer and steel industry wastes by Vinod K. Gupta; Imran Ali; Suhas; Vipin K. Saini (556-563).
The removal of 2,4-dichlorophenoxyacetic acid (2,4-D) and carbofuran from aqueous solution was studied by using fertilizer industry waste (carbon slurry) and steel industry wastes (blast furnace slag, dust, and sludge) as adsorbents in batch. Adsorption was found to be in decreasing order: carbon slurry, blast furnace sludge, dust, and slag, respectively. Carbonaceous adsorbent prepared from carbon slurry exhibited the uptake capacity of 212 and 208 mg g−1 for 2,4-D and carbofuran, respectively at 25 °C and pH 7.5. Adsorption equilibrium, kinetics, and thermodynamics were investigated as a function of initial pH, temperature, and pesticide concentrations. Equilibrium data fitted well to the Langmuir equilibrium model in the studied concentration range of 2,4-D and carbofuran at all the temperatures studied. Two simplified models, including pseudo-first-order and pseudo-second-order kinetic models, were used to test the adsorption kinetics. Adsorption of 2,4-D and carbofuran on carbon slurry at 25, 35, and 45 °C could be best fitted in the pseudo-second-order kinetic model. Pore diffusion was confirmed as the essential rate-controlling step with the help of Bangham's equation.Adsorption isotherms of 2,4-D on carbonaceous adsorbent at different temperatures.
Keywords: Pesticides; Industrial wastes; Adsorbent; Activated carbon; Adsorption;
Line of charges in electrolyte solution near a half-space by Tian Tang; Anand Jagota; Chung-Yuen Hui (564-571).
The effect of a half-space on counterion condensation around a line of charges in electrolyte solution is examined in the framework of Debye–Hückel electrostatics. The half-space substrate is allowed to be a conductor, a dielectric, or a semiconductor. Counterions are predicted to be released completely as the line of charges approaches a conducting substrate. When it approaches a dielectric substrate, depending on the ratio of solvent to substrate dielectric constant, there are three possibilities: (1) ε sol / ε sub < 1 ; the counterions are partially (or completely) released; (2) ε sol / ε sub = 1 ; the amount of condensation remains unchanged; and (3) ε sol / ε sub > 1 ; more counterions condense. Depending on the relative magnitude of screening lengths in the semiconductor and in the solution, its effect on condensation follows either that of a metal or that of a dielectric. For the case of a moderately doped silicon substrate, condensation is predicted to be similar to that for a dielectric.
Keywords: Counterion condensation; Line of charges; Half-space; Electrostatic interaction;
Line of charges in electrolyte solution near a half-space by Tian Tang; Chung-Yuen Hui; Anand Jagota (572-579).
The electric potential of a single charge in electrolyte solution near a dielectric or a semiconducting half-space is determined in closed form when the electrostatics is described by the linear Debye–Hückel (D–H) equation. The electric potential strongly depends on the Debye length of the solution, the substrate-to-solution dielectric constant ratio, and the Debye length of the semiconductor. The technique of Hankel transforms is shown to be a useful tool in solving such axially symmetric boundary value problems for the D–H equation.Electric field of a single charge in an electrolyte solution and above a half-space is determined in closed form for different electronic properties of the half-space.
Keywords: Electric field; Single charge; Half-space; Debye–Hückel; Hankel transform;
Microfluidic light scattering as a tool to study the structure of aqueous polymer solutions by Alexander I. Norman; Wenhua Zhang; Kathryn L. Beers; Eric J. Amis (580-588).
A small-angle light scattering (SALS) apparatus, coupled with a specially designed microfluidic device is shown to monitor the formation and subsequent size distribution of giant multilamellar vesicles of a diblock copolymer in aqueous solution. The closed-face design, fabricated between glass slides using a UV-curable optical adhesive, incorporates multiple inlets, a mixing system, and a viewing window to perform on-line SALS. The mixing of each component is tested using polystyrene latex microspheres. Vesicles of the block copolymer, EO6BO11 in aqueous solution are formed on the SALS chip and the pair distance distribution function determined using an inverse Fourier transformation of the scattered intensity to quantify the population and distribution for a range of vesicle sizes. These experiments provide demonstrations of how SALS on a microfluidic device can be used as a rapid screening tool to optimize processing conditions for a range of polymer solutions.A small-angle light scattering apparatus is coupled with microfluidic technology. We show, using polymeric vesicles as an example, the potential for this technique as a screening tool for polymer formulations.
Keywords: Microfluidics; Small-angle light scattering; Vesicles; Screening tools;
Real polymer size from the ideal chain molecules model in a diffusive Minkowskian spacetime by Stefano A. Mezzasalma (589-592).
The universal exponent ( ν r ) of the real polymer size (i.e., the excluded volume chain) is derived from constraining the ideal coil model ( ν i = 1 2 ) to a Minkowski-type diffusive spacetime. The square end-to-end distance was expanded in wavenumber power series, whence the leading contribution is extracted according to previously proposed Lorentz transforms acting in Brownian media. In the end, it turns out ν i ≃ ν r sin ( 1 ) , in good agreement with predictions of the phase transition theory for critical phenomena.Scheme of length contraction (a) and time dilation (b) in the spacetime scaling of the ideal chain within a Brownian relativity approach.
Keywords: Polymer solutions; Real chain size; Universal scaling;
Production of microsized PMMA droplets using electrospraying with various auxiliary fields by Geunhyung Kim; Jongha Park; Houkseop Han (593-598).
To fabricate uniform nano/microsized beads using the electrospraying process, poly(methylmethacrylate) (PMMA) polymer solution is ejected from a reservoir tip to form suspended droplets using the force of a controllable syringe pump. Using a newly designed electrode connected to the nozzle and a field-controllable target electrode, we obtained uniform microsized beads of the solution. Moreover, by using a two-axis x – y stage, we could obtain selective coverage of microsized PMMA droplets on an insulating PET film. To clarify the effect of the applied field conditions, the droplets deposited on a dielectric substrate were characterized under an optical microscope.The contours of the calculated electric field near the nozzle for various auxiliary electrodes at the same field scale are described in the figure. The auxiliary electrode influenced the electric field near the nozzle tip and the shape of ellipsoidal contour of electric field can influence the meniscus of Taylor-cone in a nozzle tip.
Keywords: Electrospray; Complex electric field; PMMA;
Preparation and characterization of carbonyl iron/poly(butylcyanoacrylate) core/shell nanoparticles by J.L. Arias; V. Gallardo; F. Linares-Molinero; A.V. Delgado (599-607).
In this article a method is described to prepare composite colloidal nanoparticles, consisting of a magnetic core (carbonyl iron) and a biodegradable polymeric shell [poly(butylcyanoacrylate) or PBCA]. The method is based on the so-called anionic polymerization procedure, often used in the synthesis of poly(alkylcyanoacrylate) nanospheres designed for drug delivery. Interest of this investigation is based upon the fact that the heterogeneous structure of the particles can confer them both the possibility to respond to external magnetic fields and to be used as drug carriers. In order to investigate to what extent do the particles participate of this mixed properties, we compare in this work the physical characteristics (structure, chemical composition, specific surface area and surface electrical and thermodynamic properties) of the core/shell particles with those of both the nucleus and the coating material. This preliminary study shows that the mixed particles display an intermediate behavior between that of carbonyl iron and PBCA spheres. Electrophoretic mobility measurements as a function of pH and as a function of KNO3 concentration, show a great similarity between the core/shell and pure polymer nanoparticles. Similary, a surface thermodynamic study performed on the three types of particles demonstrated that the electron-donor component of the surface free energy of the solids is very sensitive to the surface composition. In fact, a measurable decrease of such component is found for core/shell particles as compared to carbonyl iron. We also analyzed the influence of the relative amounts of polymer and carbonyl iron on the characteristics of the composite particles: data on the coating thickness, the amount of polymer bound to the magnetic nuclei, the redispersibility characteristics of the suspensions and the surface electrical and thermodynamic properties, suggest that the optimal synthesis conditions are obtained for a 4/3 initial monomer/carbonyl iron weight ratio.
Keywords: Biodegradable polymers; Carbonyl iron; Coating; Core/shell colloidal particles; Drug delivery systems; Electrophoresis; Magnetic carrier technology; Magnetic colloids; Magnetic targeted carriers; Poly(butylcyanoacrylate); Surface thermodynamics;
Layer-by-layer assembly of mucin and chitosan—Influence of surface properties, concentration and type of mucin by Olof Svensson; Liselott Lindh; Marité Cárdenas; Thomas Arnebrant (608-616).
Bovine submaxillary mucin (BSM) and chitosan were used to build layer-by-layer structures on solid substrates. The build-up was monitored using in situ ellipsometry to obtain time resolved values of the thickness and adsorbed amount. Additionally surface morphology during build-up was studied by atomic force microscopy (AFM). It was found that the adsorbed amount of the film increases approximately linearly with each deposition cycle on hydrophobized silica whereas construction on silica was found not to be possible at the experimental conditions used. We conclude that sufficient amount of the first mucin layer is crucial for the subsequent multilayer formation. The complex build-up kinetics on hydrophobized silica is characterized by adsorption and redissolution processes and the overall growth is the sum of both processes. AFM imaging on hydrophobized silica also confirmed the presence of redissolution processes and chitosan addition led to a reduction both in the number of surface aggregates and in the roughness of the surface. The present work also shows that by adjusting the relative concentrations of the polyelectrolytes it is possible to change the growth rate considerably. The final structures after deposition of 8 bilayers were found to have a high content of water and film stability test revealed that a substantial amount dissolves when increasing electrolyte concentration or pH of the ambient solution. Human mucin from saliva (MUC5B) was also used to create multilayers with chitosan on hydrophobized silica and it was revealed that no redissolution appears to be present in this system.Mucin (BSM) and chitosan were used to build layer-by-layer structures on hydrophobized silica by alternating adsorption from ambient solution. The figure shows adsorbed amount (mg/m2) from ellipsometric measurements versus the number of adsorption cycles.
Keywords: Multilayer; PEM; Ellipsometry; Adsorption; Glycoprotein; Polysaccharide; Biomacromolecule; Hydrophobic surface; Hydrophilic surface; Biopolymer;
Interactions of β-lactoglobulin with sodium decylsulfonate, decyltriethylammonium bromide, and their mixtures by Run-Chao Lu; Ao-Neng Cao; Lu-Hua Lai; Jin-Xin Xiao (617-625).
The interactions of β-lactoglobulin (BLG) with anionic surfactant sodium decylsulfonate (C10SO3), cationic surfactant decyltriethylammonium bromide (C10NE), and the mixtures of cationic–anionic surfactants (C10NE–C10SO3) were investigated by circular dichroism (CD) and fluorescence methods. At pH 7.0, C10NE and the C10NE-rich surfactant mixtures of C10NE–C10SO3 could form precipitates with BLG, while C10SO3, equimolar mixtures of C10NE–C10SO3, or C10SO3-rich mixtures of C10NE–C10SO3 form homogeneous solutions with BLG. CD observed that both C10NE and C10SO3 could change the BLG structure. The effects of the mixtures of C10NE–C10SO3 on BLG structure depended on the ratio of C10NE to C10SO3. The C10NE-rich or the C10SO3-rich mixtures of C10NE–C10SO3 could significantly affect BLG structure, while the equimolar mixtures of C10NE–C10SO3 exhibited weaker interaction with BLG. Fluorescence measurements showed that both C10NE and C10SO3 could induce the enhancement of fluorescence of BLG, and C10NE enhanced the BLG fluorescence more than C10SO3 did. The effect of the mixtures of C10NE–C10SO3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C10NE in C10NE–C10SO3 mixtures.C10NE enhanced the BLG fluorescence more than C10SO3 did (a), and the effect of the mixtures of C10NE–C10SO3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C10NE in C10NE–C10SO3 mixtures (b).
Keywords: β-Lactoglobulin; Sodium decylsulfonate; Decyltriethylammonium bromide; Cationic–anionic surfactants; Circular dichroism; Fluorescence;
A calorimetric evaluation of the interaction of amphiphilic prodrugs of idebenone with a biomembrane model by R. Pignatello; V.D. Intravaia; G. Puglisi (626-635).
Lipoamino acids (LAA) are useful promoieties to modify physicochemical properties of drugs, namely lipophilicity and amphiphilicity. The resulting membrane-like character of drug–LAA conjugates can increase the absorption profile of drugs through cell membranes and biological barriers. To show the role of amphiphilicity with respect to lipophilicity in the interaction of drugs with biomembranes, in the present study we evaluated the mode of such an interaction of lipophilic conjugates of LAA with the antioxidant drug idebenone (IDE). DSC analysis and transfer kinetic studies were carried out using dimyristoylphosphatidylcholine (DMPC) multilamellar liposomes (MLVs) as a model. For comparison, two esters of IDE with alkanoic acids were synthesized and included in the analysis. The experimental results indicate that based on their different structure, IDE–LAA conjugates interacted at different levels with respect to pure IDE with DMPC bilayers. In particular, a progressive penetration inside the vesicles was observed upon incubation of IDE–LAA compounds with empty liposomes. The enhanced amphiphilicity of the drug due to the LAA moieties caused more complex interactions with DMPC bilayers, compared to those registered with the native drug or IDE alkanoate esters.The lipophilic antioxidant drug idebenone was converted into amphiphilic prodrugs by means of conjugation with short-chain 2-alkylamino acids. DSC analysis and transfer kinetic studies were performed to evaluate their mode and entity of interaction with a biomembrane model (DMPC liposomes).
Keywords: Idebenone; Lipoamino acids; Lipophilicity; Amphiphilicity; DSC; Biomembrane model;
Comparison of the conformational stability of the non-native α-helical intermediate of thiol-modified β-lactoglobulin upon interaction with sodium n-alkyl sulfates at two different pH by J. Chamani (636-646).
Bovine β-lactoglobulin assumes a dimeric native conformation at neutral pH, while the conformation at pH 2 is monomeric but still native. β-lactoglobulin has a free thiol at Cys121, which is buried between the β-barrel and the C-terminal major or α-helix. This thiol group was specifically reacted with DTNB (5,5′-dithiobis(2-nitrobenzoic acid)) at pH 7.5 and 2, producing a modified β-lactoglobulin containing a mix disulfide bond with 5-thio-2-nitrobenzoic acid (TNB). β-Lactoglobulin is a predominantly β-sheet protein, although it has a markedly high intrinsic preference for α-helical structure. The formation of non-native α-helical intermediate of thiol modified β-lactoglobulin (TNB-β-LG) was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at pH 7.5 and 2. The conformation and stability of non-native α-helical intermediate (αI) state of TNB-β-LG were studied by circular dichroism (CD), fluorescence and differential scanning calorimetry (DSC) techniques. The effect of n-alkyl sulfates on the structure of αI state at both pH was utilized to investigate the contribution of hydrophobic interactions to the stability of αI intermediate. The present results suggest that the folding reaction of β-LG follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the native state of β-LG at pH 2 with more positive charges repulsion than at pH 7.5. Then TNB-β-LG will become a useful model to analyze the conformation and stability of the intermediate of protein folding.Absorption spectra of intact β-LG (1) and TNB-β-LG (2) at pH 2. For comparison, the absorption spectra of the oxidized (dashed curves) and reduced (3) forms of DTNB are included, in which the spectrum of the DTNB represents one molecule of TNB.
Keywords: TNB-β-LG; n-Alkyl sulfates; Hydrophobicity; Alpha-helix; Non-native alpha-helical; Non-hierarchical folding;
The effect of surface hydrophilicity on the behavior of embryonic cortical neurons by D.R. Nisbet; S. Pattanawong; J. Nunan; W. Shen; M.K. Horne; D.I. Finkelstein; J.S. Forsythe (647-655).
The aim of this study was to investigate the interaction of mouse embryonic cortical neurons on PLLA and PLGA substrates, which were partially hydrolysed using potassium hydroxide (KOH). The chemical and topographical properties of the surfaces were characterized, and it was discovered that there was a decrease in the hydrophilicity for the PLLA with increasing concentration of KOH. This was due to chemical modifications to the surfaces of the substrates. Alternatively for the PLGA substrate, only the 0.1 M KOH treated sample had a significantly different hydrophilicity highlighting that surface erosion resulted at higher concentrations. The morphology of the neurons grown on the two substrates were compared to polyDlysine (positive control). The neurons formed colonies on all of the substrates, but were dramatically reduced in size in the case of the 0.1 M KOH treated substrates. This finding was attributed to the increases in cell spreading and the size of the cells, as they were larger, more elongated and bipolar like those on the positive control. However, there was a significant decrease in the total number of live cells per unit area. Therefore, on these materials when there was increased cellular spreading there was significantly higher cell death. Furthermore, unlike the 0, 0.2, and 0.4 M KOH treated substrates, there was an absence of large bundles of axons that extended between colonies on the 0.1 M sample, instead exhibiting short axons that grew in free space.The interaction of embryonic cortical neurons on a series of highly characterized poly(α-hydroxy esters) substrates was investigated. Colony formation and neurite outgrowth was largely governed by the hydrophilicity and chemistry of the surfaces.
Keywords: Surface hydrophilicity; Neurons; Poly(α-hydroxy esters); Colonization;
A modeling approach to describe the adhesion of rough, asymmetric particles to surfaces by Sean Eichenlaub; Gautam Kumar; Stephen Beaudoin (656-664).
A combined theoretical and experimental study of the adhesion of alumina particles and polystyrene latex spheres to silicon dioxide surfaces was performed. A boundary element technique was used to model electrostatic interactions between micron-scale particles and planar surfaces when the particles and surfaces were in contact. This method allows quantitative evaluation of the effects of particle geometry and surface roughness on the electrostatic interaction. The electrostatic interactions are combined with a previously developed model for van der Waals forces in particle adhesion. The combined model accounts for the effects of particle and substrate geometry, surface roughness and asperity deformation on the adhesion force. Predictions from the combined model are compared with experimental measurements made with an atomic force microscope. Measurements are made in aqueous solutions of varying ionic strength and solution pH. While van der Waals forces are generally dominant when particles are in contact with surfaces, results obtained here indicate that electrostatic interactions contribute to the overall adhesion force in certain cases. Specifically, alumina particles with complex geometries were found to adhere to surfaces due to both electrostatic and van der Waals interactions, while polystyrene latex spheres were not affected by electrostatic forces when in contact with various surfaces.A theoretical and experimental study of the adhesion of alumina particles and polystyrene latex spheres to silicon dioxide was performed. The effects of roughness and geometry were investigated.
Keywords: Particle adhesion; Electrostatics; van der Waals forces; Roughness; Atomic force microscopy; Post CMP cleaning;
The characterisation of rough particle contacts by atomic force microscopy by M. George; D.T. Goddard (665-672).
An Atomic Force Microscopy (AFM) reverse imaging technique has been used to determine the contact zone topography of glass and UO3 particles in contact with flat mica substrates. A method is proposed that uses this topography to determine an effective asperity radius of curvature for the contacting particle. Application of the method has been found to be consistent with established contact mechanics models, for both glass and UO3 particle probes that present significantly different surface roughness. The method proposed is straightforward to apply and offers a greater insight into the influence of particle micro- and nano-roughness on adhesion. This is important for applications that rely on the control of granular flow such as pellet or tablet manufacture.
Keywords: Adhesion; Surface roughness; Atomic force microscopy; Contact radius;
The dispersion of natural oils in de-gassed water by M.J. Francis; N. Gulati; R.M. Pashley (673-677).
Recent studies have demonstrated that pure hydrocarbon oils can be dispersed in water as fine droplets without the use of additives. The high interfacial tension between hydrocarbons and water is expected to cause cavitation between oil droplets during separation. This cavitation is aided by dissolved atmospheric gases present in both the oil and water. Their removal allows oil droplets to be readily dispersed in water. In this paper we report on the effect of the de-gassing process on the dispersion of several natural, water immiscible oils. These natural, mixed oils are eucalyptus, lavender and tea tree oil. Although these oils are mixtures and in some cases not as hydrophobic as those used in the earlier studies, the effect of de-gassing substantially enhances their dispersion, producing micron-sized droplets without the need for additives. Dispersions of these natural oils in pure water have a wide range of uses where purity is an advantage, for example, in skin cleaning products and oral sprays.In this paper we report on the effect of de-gassing on the dispersion of several natural, water immiscible oils. These oils are eucalyptus, lavender and tea tree oil.
Keywords: Dispersion; Emulsion; Natural oils; De-gassing;
The preparation of Pt nanoparticles by methanol and citrate by Chia-Shiang Lin; Maksudur R. Khan; Shawn D. Lin (678-685).
Platinum nanoparticles of 2–3 nm average size and ca. ±2 nm distribution can be successfully prepared by methanol reduction while using sodium citrate as the stabilizer. Sol formation was investigated by UV–visible spectroscopy and EXAFS (extended X-ray absorption fine structure spectroscopy). The formation of Pt nanoparticles was confirmed by the presence of Pt–Pt bonding in the solution after a certain induction period in methanol-reduced sol with or without citrate. The possible two-step reduction of Pt(IV) was revealed by correlating EXAFS, UV–visible spectra and pH data. The presence of citrate resulted in a smaller Pt–Pt coordination number and a slower sol formation process. All these results prove that citrate acted as the stabilizer in this synthesis.Pt nanoparticles of ca. 2 nm average size can be successfully prepared by methanol reduction while using sodium citrate as the stabilizer. The presence of citrate resulted in a smaller Pt–Pt coordination number and a slower sol formation process.
Keywords: Pt nanoparticle; EXAFS; Pt–Pt coordination number; Citrate;
The influence of ionic and nonionic surfactants on aggregative stability and electrical surface properties of aqueous suspensions of titanium dioxide by Nataliya H. Tkachenko; Zinoviy M. Yaremko; Cornelia Bellmann; Mykhaylo M. Soltys (686-695).
The influence of concentration of nonionic TRITON X-100 and anionic ATLAS G-3300 surfactants, and pH of medium on the size and zeta-potential of TiO2 particles in the water suspensions has been studied. Suspensions have been prepared by mixing of the titanium dioxide in the suitable mediums at 10 min and 6 h correspondingly. It was established, that the duration of mixing of the suspensions has an essential influence on the dependence of zeta-potential and size of particles versus concentration of surfactant. However, the duration of mixing does not influence the dependence of electrical conductivity and pH of the suspensions on concentration of surfactant. It is shown that anionic ATLAS G-3300 surfactant is more effective stabilizator of aqueous suspensions of titanium dioxide, than nonionic surfactants of TRITON X-100. It is found that hydrophobic interaction has important role in the processes of stabilization of suspensions for nonionic surfactant, and for anionic surfactant—moving of ψ δ -planes into solution's depth.The dependence of zeta-potential and particle diameter of the TiO2 suspensions in the 1 × 10 −3 mol / L KCl solution versus concentration of ATLAS G-3300. Open symbols: suspension was mixed for 10 min; closed ones—for 6 h.
Keywords: Titanium dioxide; Aggregative stability; Electrical surface properties; ATLAS G-3300; TRITON X-100;
Orientation of irreversible adhesion of spherical particles on prolate spheroidal collectors by Joseph F. Jones; Dale Waters; Matthew Flamm; Darrell Velegol (696-702).
When one sphere adheres to a second sphere, the location or orientation of the adhesion on the second sphere is seldom considered. However, when a sphere adheres to a prolate spheroid, the orientation of the adhesion is sometimes critical. We have performed Brownian dynamics simulations to predict the orientation of adhesion of a sphere on a prolate spheroid. When the spheroid has a high rotational diffusion coefficient, simulations show that the spherical particle adheres near the end of the spheroid. We tested our model experimentally for two systems: (1) oppositely-charged spherical and spheroidal colloids and (2) like-charged colloidal spheres and E. coli K-12 D21 bacteria. For the latter case, the spheres have previously been shown to adhere only to one end of the bacterium. Experiments in case (1) support the results of the simulations, while data from case (2) do not agree with predictions. Case (2) data reveal that the end-on adhesion of the spheres on the bacteria is not a purely Brownian phenomenon.
Keywords: Bacterial adhesion; Adhesion orientation; Preferential adhesion; Spheroidal particles;
The equal-size binary breakage problem: Evolution toward a steady shape or periodic behavior? by Margaritis Kostoglou (703-712).
During the last few years, the self-similar particle size distribution for a particle population undergoing breakage in equal size fragments has been derived using approximating, numerical, and analytical means. But very recently it was shown [N.V. Mantzaris, J. Phys. A Math. Gen. 38 (2005) 5111] through transient simulation of the breakage process that the particle size distribution in case of breakage in two equal fragments, never attains a steady shape, i.e., a self-similar form. The new results give rise to questions about the real meaning and utility of the previously derived self-similar distributions for these systems. The scope of the present work is to answer these questions and it is attempted using only analytical (exact) means for the solution of the transient breakage problem. In doing so, the very interesting and rich underlying structure and properties of the solutions of the equal size breakage problem (seemingly, very simple) are revealed. It appears that the utility of the known self-similar distributions for this particular problem has to be redefined but yet not entirely abandoned.By examining in detail the equal size binary breakage problem, it is shown that at large time the particle size distribution (PSD) can take a constant shape or oscillates depending on the specific set of conditions (σ is PSD dispersivity, τ F is transformed time).
Keywords: Breakage equation; Binary equal size breakage; Analytical solutions; Self-similar distribution; Large time asymptotics; Periodic oscillation;
SiO2/Cr monolayers and formation of polyethylene films by Jun Wang; Hugo Leeman; Robert A. Schoonheydt (713-718).
1,3,5-tribenzylhexahydro-1,3,5-triazine-CrCl3 (TAC-CrCl3) was supported on monodisperse Stöber silica and on commercial silica particles. The monolayers of these catalyst particles were successfully prepared with Langmuir–Blodgett technique. The effect of TAC-CrCl3 molecules on the ordering and film-forming of the silica particles was investigated. The particles arrange in domains of hexagonal ordering, but the ordering of particles in the monolayer decreases with increasing Cr loading. These hybrid monolayers are active polymerization catalysts. After polymerization, a relatively rough layer of polyethylene molecules covers the catalyst monolayer and this layer is hydrophobic. The monolayers and the polymers coating films were characterized by IR, UV–vis-NIR, and SEM. The method provides a way to fabricate polyethylene films on silica monolayers.SEM picture of sSiO2(MeOH)/Cr-0.5 catalyst monolayer.
Keywords: Silica; Monolayer; Cr; Polymerization; Organization;
Pore structure of the packing of fine particles by R.Y. Yang; R.P. Zou; A.B. Yu; S.K. Choi (719-725).
This paper presents a numerical study of the pore structure of fine particles. By means of granular dynamics simulation, packings of mono-sized particles ranging from 1 to 1000 μm are constructed. Our results show that packing density varies with particle size due to the effect of the cohesive van der Waals force. Pores and their connectivity are then analysed in terms of Delaunay tessellation. The geometries of the pores are represented by the size and shape of Delaunay cells and quantified as a function of packing density or particle size. It shows that the cell size decreases and the cell shape becomes more spherical with increasing packing density. A general correlation exists between the size and shape of cells: the larger the cell size relative to particle size, the more spherical the cell shape. This correlation, however, becomes weaker as packing density decreases. The connectivity between pores is represented by throat size and channel length. With decreasing packing density, the throat size increases and the channel length decreases. The pore scale information would be useful to understand and model the transport and mechanical properties of porous media.Delaunay tessellation is employed to characterise the pore structure of fine particles. The figures show the representative spatial distribution and connectivity of pores (left), the statistical distributions of pore size for different packing densities (middle), and the joint distribution of the effective throat diameter and channel length (right).
Keywords: Packing; Fine particles; Porous media; Delaunay tessellation; Discrete element method;
Synthesis of CeO2@SiO2 core–shell nanoparticles by water-in-oil microemulsion. Preparation of functional thin film by F. Grasset; R. Marchand; A.-M. Marie; D. Fauchadour; F. Fajardie (726-732).
Synthesis of nanoparticles under restricted environment offered by water-in-oil (W/O) microemulsions provides excellent control over particle size and shape, and inter-particle spacing. Such an environment has been involved to synthesize silica nanoparticles with a CeO2 core, so-called CeO2@SiO2. Aqueous fluids made up of ceria nanoparticles with a size close to 5 nm have been used as the water phase component. The starting CeO2 sols and obtained CeO2@SiO2 nanoparticles have been characterized by dynamic light scattering (DLS), X-ray diffraction, scanning and transmission electron microscopy, and specific surface area measurements. The microemulsion process has been characterized by DLS. Preliminary results on CeO2@SiO2 thin films are presented.
Keywords: Nanocolloids; Microemulsion; DLS; CeO2; Silica; Core–shell; Nanoparticles;
In situ probing of insulin aggregation in chromatography effluents with spectroturbidimetry by Chi-Ming Yu; Chim Yong Chin; Elias I. Franses; Nien-Hwa Linda Wang (733-739).
Probing protein aggregation in situ is quite important for analyzing and developing chromatographic protein purification processes. A spectroturbidimetry method with a photodiode array detector is developed and tested for probing insulin aggregation in solution and determining the aggregation number, n m . All aggregates examined are in the Rayleigh light scattering regime, where the turbidity between 400 and 350 nm is proportional to λ −4 . Insulin at 25 °C in 3.5 N acetic acid is mainly monomeric (non-aggregated). At 25 °C and lower acetic acid concentrations, from 0.1 to 1 N, the average insulin aggregation number n m ranges from 2.9 to 1.6. Aggregates, with n m = 2 – 3 , are found in 2.6 N acetic acid with 20 vol% acetonitrile. In 0.8 N acetic acid with 20 vol% denatured ethanol, n m = 1.2 . At 4 °C, as acetic acid concentration decreases from 3.5 to 0.1 N, n m decreases from 2.4 to 1.8. In 2.8 N acetic acid with 20 vol% denatured ethanol at 4 °C, insulin exists mainly in monomer form. In situ probing of size exclusion chromatography, SEC, effluents in 3.5 N acetic acid at 4 °C shows n m = 1.6 at the fronting portion (a mixture of monomers and dimers or other oligomers) and n m = 1.1 (mostly monomers) at the tailing portion of the main peak. In another example, for LysPro-insulin in reversed phase chromatography at 4 °C, complex elution patterns and broad peaks are due to substantial aggregation. For a linear gradient of acetonitrile from 10 to 60 vol% at 4 °C, n m ranges from 2.2 to 12, in order of elution. For a linear gradient of ethanol from 30 to 50 vol% at 4 °C, n m ranges from 14 to 27, in order of elution. Analytical HPLC results at 25 °C imply that the aggregates are reversible.An in situ spectroturbidimetry method with a photodiode array detector is developed and tested for probing insulin aggregation in solution and determining the aggregation number, n m .
Keywords: Insulin reversible aggregation; In situ probing; Size exclusion chromatography; Spectroturbidimetry; Rayleigh light scattering;
Stability of the aqueous suspensions of nanotubes in the presence of nonionic surfactant by Milana O. Lisunova; Nikolai I. Lebovka; Olexander V. Melezhyk; Yurie P. Boiko (740-746).
Stability of aqueous suspensions of multiwalled carbon nanotubes (MWNTs) and their percolation behavior are investigated. Nanotubes of aqueous suspensions show a strong tendency to aggregation and networking into electroconductive clusters. The percolation threshold of the electrical conductivity is rather low and of order φ ≈ 0.01 (where φ is the volume fraction), which can be explained by the high aspect ratio of MWNTs. Strong influence of the nonionic surfactant Triton X-305 on the colloidal stability of aqueous suspensions of MWNTs is observed. Addition of surfactant exerts a stabilizing effect at surfactant concentration C s proportional to the weight concentration C of MWNTs, C s ≈ C mol / dm 3 . The transient behavior of electrical conductivity in the aqueous suspensions is explained by fractal aggregation processes. The fractal dimension is shown to be sensitive to the surfactant concentration C s .This work discusses the relations between colloidal stability and percolation phenomena in aqueous suspensions of multiwalled carbon nanotubes. The transient changes of electrical conductivity were explained by fractal clusters formation.
Keywords: Nanotubes; Aqueous suspensions; Electrical conductivity; Percolation; Fractal dimension;
Evidences of segregated SnO2 type nanoparticles coating layered double hydroxide at moderate temperature by Mourad Intissar; François Malherbe; Vanessa Prévot; Fabrice Leroux (747-753).
A series of layered double hydroxide (LDH) materials prepared by classical coprecipitation in the presence of divalent Co2+, trivalent Al3+, and tetravalent Sn4+ cations have been investigated as a function of the temperature. As illustrated for the cation composition (Co; Al; Sn) of (0.75; 0.175; 0.075), the segregation of SnO2-type nanodomains in an interphasing LDH sand-rose region is directly evidenced by transmission electron microscopy and selected area electron diffraction (TEM/SAED). At moderate temperature (⩽400 °C) the local environment around the cobalt cations is strongly modified, whereas the local structure is found to be unchanged in the vicinity of the tin cations. It is explained on the basis of the breakdown of the lamellar assembly and of the partial oxidation of Co2+ cations and that tin dioxide domains are still segregated from LDH particles. Even if the tin dioxide component does not participate from a structural point of view in the LDH composition, its beneficial effect on the textural properties is significant, increasing the specific surface area and narrowing the pore size distribution.Direct evidence of the segregation of tin cation in nanodomain coating LDH particles and investigation of the local structure and of the textural properties.
Keywords: Layered double hydroxide; Local structure; X-ray absorption spectroscopy; Nitrogen gas adsorption;
Arrangement, conformation, and mobility of surfactant molecules intercalated in montmorillonite prepared at different pillaring reagent concentrations as studied by solid-state NMR spectroscopy by Xiaoyan Wen; Hongping He; Jianxi Zhu; Yang Jun; Chaohui Ye; Feng Deng (754-760).
The arrangement, conformation, and mobility of dodecyltrimethylammonium cations (DDTMA+) intercalated in montmorillonite prepared with different pillaring reagent concentrations have been studied by 13C relaxation time measurement, cross-polarization dynamics, and two-dimensional proton wide-line separation (2D WISE) spectroscopy, as well as X-ray powder diffraction (XRD). We demonstrate that the arrangement of DDTMA+ and the mobility of various groups are different, depending on the pillaring concentration, but the conformations of alkyl chains are similar. XRD experiments illustrate that at three different pillaring concentrations (DDmt0.2, DDmt0.5, and DDmt1.0), the organic cations adopt a lateral-monolayer, lateral-monolayer, and pseudotrilayer arrangement, respectively. 13C MAS NMR reveals that the alkyl chains at the three concentrations uniformly display a large amount of mixed trans and gauch conformation (disordered) and a small amount of trans conformation (ordered). 13C spin-lattice relaxation time and 1H–13C cross-polarization dynamics measurement, along with 2D WISE NMR experiments, indicate that the mobility is much different for various groups at a given concentration and for a given group at different concentrations. At each concentration N-methyl unusually possesses the highest mobility, even exceeding that of the terminal methyl; at different concentrations the N-methyl and terminal methyl in DDmt1.0 exhibit the highest mobility compared with the other two samples.The arrangement of DDTMA+, and the mobility of various groups in montmorillonite are different, depending on the pillaring concentration, but the conformation of alkyl chains is similar.
Keywords: Montmorillonite; Alkylammonium; Solid state NMR; Dynamics; 2D WISE NMR;
Size control for two-dimensional iron oxide nanodots derived from biological molecules by Masato Tominaga; Manabu Matsumoto; Kazuki Soejima; Isao Taniguchi (761-765).
We demonstrated the fabrication of size-controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces. Ferritin molecules were immobilized onto 3-aminopropyltrimethoxysilane (3-APMS)-modified silicon surfaces by electrostatic interactions between negatively charged amino acids of ferritin molecules and amino terminal functional groups of 3-APMS. Heat treatments were performed at 400 °C for 60 min to fabricate two-dimensional nanodots based on ferritin cores. XPS and FT-IR results clearly indicate that ferritin shells were composed of amino acids and 3-APMS modifiers on silicon surfaces were eliminated by heat treatment. Nanodots on substrate surfaces corresponded to iron oxides. The size of nanodots was tunable in the range of 0–5 (±0.75) nm by in situ reactions of iron ion chelators with ferritin molecules immobilized on substrates before heat treatment.The fabrication of size controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces was demonstrated. The size of nanodots was tunable in the range of 0–5 (±0.75) nm by in situ reactions with iron ion chelators with ferritin molecules.
Keywords: Ferritin; Protein; Nanodots; Iron oxide; Chelator; AFM;
Electrochemically enhanced adsorption of phenol on activated carbon fibers in basic aqueous solution by Yanhe Han; Xie Quan; Shuo Chen; Huimin Zhao; Chunyue Cui; Yazhi Zhao (766-771).
Electrosorption isotherms and thermodynamics of phenol on activated carbon fibers (ACFs) in basic solution, as well as the factors (bias potential, initial concentration, and electrolyte) affecting adsorption/electrosorption kinetics, were investigated. The kinetics, which followed the Lagergren adsorption rate law, exhibited a variety of responses depending on bias potential, initial concentration, and electrolyte. The electrosorption isotherms were in agreement with the classical models of Langmuir and Freundlich, but the former gave more satisfactory correlation coefficients. With electrosorption at a bias potential of 700 mV from the basic solution, a nearly 10-fold enhancement of maximum adsorption capacity was achievable. The electrosorption free energy ( Δ G ads ), enthalpy ( Δ H ads ), and entropy ( Δ S ads ) of phenol on the ACFs were calculated from adsorption isotherms at different temperatures. The results indicated that electrosorption of phenol in basic solution was spontaneous and exothermic. Furthermore, it was assessed that electrosorption occurred by dipole–dipole interaction with Δ H ads of − 20.14 kJ mol −1 besides suppositional electrostatic interaction.The enhanced adsorption of phenol on activated carbon fibers in basic solution by electrochemical polarization was investigated. With electrosorption at potential of 700 mV, nearly ten-fold enhancement of adsorption capacity was achievable.
Keywords: Carbon fibers; Phenol; Electrosorption kinetics; Electrosorption isotherms; Thermodynamics;
Surface potential of hematite in aqueous electrolyte solution: Hysteresis and equilibration at the interface by Tajana Preočanin; Ana Čop; Nikola Kallay (772-776).
Electrostatic potential at the inner plane of the hematite aqueous interface, i.e., surface potential, was measured by means of a single-crystal hematite electrode. Acidic solutions were titrated with base and then back-titrated with acid. Surface potentials were evaluated from electrode potentials by setting the zero value at the isoelectric point. In the case of fast titrations the equilibration time was approximately 10 min, and significant hysteresis was obtained, more pronounced at higher electrolyte concentrations. Hysteresis disappeared in slow titration runs when the equilibration time was extended up to 120 min, and also when ultrasound was applied. Hysteresis was observed in the pH region close to neutrality, where the concentrations of potential-determining H+ and OH− ions are low. Equilibration was fast in acidic and basic regions. These results are explained on the basis of the kinetics of surface reactions, supported by the following rate of single-crystal electrode equilibration. It is concluded that the equilibration rate at the interface is specific for a given system and is not a general phenomenon. As several systems may undergo fast equilibration, such data may be regarded as equilibrium data and interpreted by the surface complexation model. In other cases, one should perform kinetic tests and apply extended equilibration times.Surface potential at hematite aqueous interface was measured with a single-crystal electrode. Hysteresis was obtained in the acid–base titrations curves and disappeared in extremely slow titration runs.
Keywords: Surface potential; Single-crystal electrode; Surface complexation model; Hysteresis; Hematite; Surface charge; Metal oxides; Electrical double layer;
Suppression of electron-transfer characteristics of ferrocene by OTS monolayer on a silicon/electrolyte interface by Sneha A. Kulkarni; Bhalchandra A. Kakade; Imtiaz S. Mulla; Vijayamohanan K. Pillai (777-784).
The passivating behavior of self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) on an n-type Si(100) electrode with and without a redox species like ferrocene in a polar non-aqueous medium has been investigated using techniques like contact angle measurements, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to understand the role of the monolayer. The electron-transfer behavior of ferrocene is found to be drastically affected by the presence of monolayer and the reasons for these are analyzed as a function of the change in resistance, dielectric thickness and coverage of the monolayer. Electrochemical impedance analysis in the presence of ferrocene gives the monolayer coverage as 0.998 and the apparent rate constant calculated from this gives 4.85 × 10 −12 cm s −1 in comparison with 4.4 × 10 −8 cm s −1 for a similar electrode without any monolayer. A positive shift of 200 mV in the flat-band potential after monolayer formation also suggests the covalent coupling of the silane monolayer offering a protective barrier.
Keywords: Self-assembled monolayer (SAM); Octadecyltrichlorosilane (OTS); Ferrocene; Rate constant; Cyclic voltammetry; Impedance analysis;
Role of microenvironment in the mixed Langmuir–Blodgett films by S.A. Hussain; P.K. Paul; D. Bhattacharjee (785-790).
This paper reports the π–A isotherms and spectroscopic characteristics of mixed Langmuir and Langmuir–Blodgett (LB) films of nonamphiphilic carbazole (CA) molecules mixed with polymethyl methacrylate (PMMA) and stearic acid (SA). π–A isotherm studies of mixed monolayer as well as the remarkable change in collapse pressure of the mixed monolayer isotherms definitely show that CA is incorporated into PMMA and SA matrices. However, CA is stacked in the PMMA/SA chains and forms microcrystalline aggregates, as is evidenced from the scanning electron micrograph picture. The nature of these aggregated species in the mixed LB films has been revealed by UV–vis absorption and fluorescence spectroscopic studies. The presence of two different kinds of band systems in the fluorescence spectra of the mixed LB films have been observed. This may be due to the formation of low-dimensional aggregates in the mixed LB films. Intensity distribution of different band systems is highly sensitive to the microenvironment of two different matrices as well as also on the film thickness.Figure shows a scanning electron micrograph (SEM) of the 10-layer mixed LB film of 0.5 M of CA in SA matrix. The aggregates with sharp and distinct edges correspond to the three-dimensional aggregates of CA in LB films. The smooth background corresponds to the PMMA matrix. The formation of distinct crystalline domains of CA, as evidenced from the SEM, provides compelling visual evidence of aggregation of CA in the LB films.
Keywords: Nonamphiphilic; Langmuir–Blodgett films; UV–vis absorption spectroscopy; Fluorescence spectroscopy;
The preparation of composite microsphere with hollow core/porous shell structure by self-assembling of latex particles at emulsion droplet interface by Xiao Dong He; Xue Wu Ge; Mo Zhen Wang; Zhi Cheng Zhang (791-796).
A submicrometer-scaled polystyrene/melamine–formaldehyde hollow microsphere composite was prepared by self-assembling of sulfonated polystyrene (SPS) latex particles at the interface of emulsion droplets and then being fixed in place using a hard melamine–formaldehyde (MF) composite layer. For control-released purposes, the influential factors that control the size and uniformity of the packed-droplets and the permeability of the composite shell, including the initial particle location, the hydrophilicity and the size of colloidal templates, the oil phase solvent and reserving time of emulsions after the addition of MF prepolymer, were further studied. Relatively uniform sized particle packed-droplets with an average diameter of 10 μm were obtained. The assembled SPS particles kept ordering and minimal conglutination after the preparation of composite microspheres, which allows of controlling the permeability from the interstices between the particles. Porous-mesh-structured MF composite layer was formed to further control the permeability. The morphology of emulsions and composite microspheres were characterized by optical microscopy, scanning and transmission electron microscopy.
Keywords: Composite microsphere; Hollow core/porous shell; Self-assembly latex particles; Emulsion droplet interface; Controlled release;
Thermodiffusional transport of electrolytes in compact clays by M. Rosanne; M. Paszkuta; P.M. Adler (797-805).
The macroscopic Soret coefficient S T was measured for three porous media, namely mica, glass powder, and natural compact clay. At a mean temperature of T ¯ = 25 ° C and with NaCl, S T for mica and glass powder was found to be equal to ( 3.1 ± 0.7 ) × 10 −3 K −1 and close to values for a free medium in agreement with theoretical predictions which are obtained under the assumption that the pressure gradient and the electric field are negligible on the pore scale. The main result is that for clay S T was found five times larger, presumably because of extra couplings with electrical phenomena. This latter measurement was confirmed by an independent technique based on the membrane potential.The macroscopic Soret coefficient S T for compact clays (open symbols) is found five times larger than for mica and glass powder (closed symbols).
Keywords: Compact clays; Soret coefficient; Membrane potential;
Effect of ionic environments on the adsorption and diffusion characteristics of serine alkaline protease enzyme in polyethersulfone ultrafiltration membranes by Sema Salgın; Serpil Takaç; Tunçer H. Özdamar (806-814).
Static adsorption of serine alkaline protease (SAP) enzyme on hydrophobic polyether sulfone (PES) ultrafiltration membranes in different ionic environments was investigated. The amount of SAP adsorbed on membranes was the lowest at its isoelectric point (IEP) where the maximum adsorption was obtained below the IEP of the enzyme. The extent of SAP adsorption in the phosphate buffer solutions including different salts followed the order: (NH4)2HPO4 > KH2PO4 > Na2HPO4−NaH2PO4 (buffer) > CaCl2 > ((NH4)2HPO4 + H2PO4 + CaCl2), which was consistent with the Hofmeister series. The zeta potentials of membranes contacted with the ionic species were calculated by streaming potential measurements and found that the increase in ionic strength decreased the electrical double layer thickness leading to a decrease in adsorption. A model based on mass balance was developed to calculate the diffusion coefficient of SAP in PES membranes. Employing experimental data evaluated in a diffusion cell along with the data of adsorption isotherms, diffusion coefficients of SAP in PES membranes in the presence of different ionic species were calculated. To detect the structural changes occurred, membrane surfaces were analysed by Fourier transform infrared-attenuated total reflectance (FTIR-ATR) measurements.Membrane fouling consists of adsorption and aggregation. Determinations of the parameters that affect the membrane fouling and developing methods for fouling analysis are important for membrane separation systems.
Keywords: Adsorption; Diffusion coefficient; Protease; Hofmeister series;
Substitution controlled molecular orientation and nanostructure in the Langmuir–Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives by Tifeng Jiao; Minghua Liu (815-822).
Three amphiphilic Schiff bases containing naphthylidene group, N-octadecyl-2′-hydroxy-naphthalenylideneamine (HNOA-1), N-(4′-octadecyloxy)-2′-hydroxy-naphthalenylideneaniline (HNOA-2), and N-(4′-N-octadecylbenzamide)-2′-hydroxy-naphthalenylideneaniline (HNOA-3), were designed and their interfacial assemblies were investigated. These amphiphiles have different substitution groups in the Schiff base moiety. It was observed that HNOA-1, being in lack of second aromatic ring, formed multilayer films at the air/water interface, while the other two compounds, with another aromatic ring and some hydrophilic groups, can be spread as monolayers on water surface. All of Schiff bases could coordinate with Cu(Ac)2 in situ in the spreading films. Both the spreading films from water and aqueous Cu(Ac)2 subphases were transferred onto solid substrates and their surface morphologies as well as molecular packing modes were investigated by a series of methods such as atomic force microscopy, Fourier transform infrared spectra and X-ray diffraction. Depending on the different substitutions, these amphiphiles showed different orientations in the Langmuir–Blodgett films. Particularly, during the process of complex formation at the air/water interface, great conformational change of the alkyl chain was observed for HNOA-2 in comparison with that of other compounds. In addition, nanofiber structures were observed for the Cu(II)-complexed HNOA-1 and HNOA-2 films.Interfacial assemblies, coordination with Cu(II) of amphiphilic naphthylidene-containing Schiff bases with different substituted groups were investigated. Different molecular orientations and the nanofibers structures were formed depending on the substitutions.
Keywords: Schiff base; Langmuir–Blodgett film; Nanofiber; Naphthylidene; Coordination;
Synthesis of micrometer-sized hard silica spheres with uniform mesopore size and textural pores by L.M. Yang; Y.J. Wang; Y.W. Sun; G.S. Luo; Y.Y. Dai (823-830).
Micrometer-sized silica spheres were prepared using a new pH-induced rapid colloid aggregation method in water-in-oil (W/O) emulsion separately with F127 and the mixture of Pluronic triblock copolymer (F127, P123, or P105) and PEG20000 as templates. All the mesoporous silica spheres exhibited high surface areas (657–1145 m2/g) and large pore volumes (0.46–2.16 ml/g). Through optimizing the synthetic conditions, hard silica spheres with narrow particle size distribution, uniform pore size, and textural pores were obtained. Finally, the mechanism of this synthetic route is discussed.SEM image of silica spheres prepared using a new ‘pH-induced rapid colloid aggregation method’ in W/O emulsion with the mixture of F127 and PEG20000 as templates.
Keywords: Silica spheres; Pluronic; Emulsion; pH-induced; Colloid aggregation;
Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties by M. Gironès; L.A.M. Bolhuis-Versteeg; R.G.H. Lammertink; M. Wessling (831-840).
The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.Silicon-based surfaces, among them microsieve membranes, were coated with a random copolymer, poly(TMSMA-r-PEGMA), which successfully reduced protein adhesion and fouling of BSA and skimmed milk.
Keywords: Silicon nitride; Microsieves; BSA fouling; PEG; Backpulsing; Air sparging; Flux stabilization;
Retention forces and contact angles for critical liquid drops on non-horizontal surfaces by A.I. ElSherbini; A.M. Jacobi (841-849).
Retention forces and drop parameters are investigated for drops on the verge of sliding on vertical and inclined surfaces. Using earlier observations of drop geometry, the retentive-force factor relating surface-tension forces to contact-angle hysteresis is reliably determined. The retention force for a drop is found to be insignificantly affected by the aspect ratio of its contour. The maximum size of a drop is predicted with good accuracy, based on the two-circle method for approximating shapes of drops. The Bond number of a critical drop is found to be constant for a given surface and liquid. A general relation is proposed between the characteristic advancing and receding contact angles. The relation is supported by a large set of contact-angle data. In the absence of θ R data, the relation allows estimating the receding contact angle and the critical drop size, using only the advancing angle.Predictions of retentive forces, based on a force-balance model are compared to measurements from the literature [C.W. Extrand, Y. Kumagai, J. Colloid Interface Sci. 170 (1995) 515] for critical drops on several surfaces. The proposed k = 48 / π 3 (Eq. (13)) fits the data with ( r = 0.98 ).
Keywords: Liquid drops; Critical size; Incipient motion; Retention; Forces; Contact angle hysteresis;
The adsorption and unfolding kinetics determines the folding state of proteins at the air–water interface and thereby the equation of state by Peter A. Wierenga; Maarten R. Egmond; Alphons G.J. Voragen; Harmen H.J. de Jongh (850-857).
Unfolding of proteins has often been mentioned as an important factor during the adsorption process at air–water interfaces and in the increase of surface pressure at later stages of the adsorption process. This work focuses on the question whether the folding state of the adsorbed protein depends on the rate of adsorption to the interface, which can be controlled by bulk concentration. Therefore, the adsorption of proteins with varying structural stabilities at several protein concentrations was studied using ellipsometry and surface tensiometry. For β-lactoglobulin the adsorbed amount (Γ) needed to reach a certain surface pressure (Π) decreased with decreasing bulk concentration. Ovalbumin showed no such dependence. To verify whether this difference in behavior is caused by the difference in structural stability, similar experiments were performed with cytochrome c and a destabilized variant of this protein. Both proteins showed identical Π – Γ , and no dependence on bulk concentration. From this work it was concluded that unfolding will only take place if the kinetics of adsorption is similar or slower than the kinetics of unfolding. The latter depends on the activation energy of unfolding (which is in the order of 100–300 kJ/mol), rather than the free energy of unfolding (typically 10–50 kJ/mol).
Keywords: Surface denaturation; Protein adsorption; Air–water interface; Surface equation of state;
Surface properties of mixed monolayers of sulfobetaines and ionic surfactants by David López-Díaz; Inmaculada García-Mateos; M. Mercedes Velázquez (858-866).
To study the influence of the head group in the properties of the mixed monolayers adsorbed at the air–water interface, the surface tension and surface potential of binary mixtures of surfactant have been determined as a function of the surfactant composition. Experiments were carried out with anionic–zwitterionic sodium dodecyl sulfate and dodecyl dimethyl ammoniopropane sulfonate (SDS/DDPS), and cationic–zwitterionic dodecyl trimethylammonium bromide and dodecyl dimethyl ammoniopropane sulfonate (DTAB/DDPS), and dodecyl trimethylammonium bromide and tetradecyl dimethyl ammoniopropane sulfonate (DTAB/TDPS). It was shown that mixed monolayers of cationic–zwitterionic surfactant exhibit small negative deviations of ideal behavior, whereas for SDS/DDPS monolayers show strong negative deviation from the ideality. Deviations of ideal behavior are interpreted by regular solution theory. The surface potential values agree very well with the concentration of the ionic component at the interface. The dynamic surface tension values show that the adsorption kinetics on the interface is a diffusion-controlled process. In monolayers with significant deviation of the ideal behavior, anionic–zwitterionic, there is some evidence of intermolecular attractions after diffusion of both surfactants at the interface.Variation of surface potential and surface mole fraction of DTAB with bulk composition for mixed monolayers of DTAB/TDPS.
Keywords: Alkyl ammonium propane sulfonate surfactants; Sodium dodecyl sulfate; Dodecyl trimethyl ammonium bromide; Mixed monolayers; Equilibrium surface tension; Dynamic surface tension; Diffusion-controlled adsorption; Surface potential; Regular solution theory;
Complex coacervation between β-lactoglobulin and Acacia gum: A nucleation and growth mechanism by Christian Sanchez; Ghozlène Mekhloufi; Denis Renard (867-873).
Complex coacervation between proteins and polysaccharides is a demixing process mainly driven by electrostatic interactions. During this process many structural transitions occur, involving the formation of soluble complexes, aggregated complexes, and coacervates. The dynamic mechanism of complexation/coacervation was studied on β-lactoglobulin (BLG)/Acacia gum (AG) mixed dispersions (0.1 wt% total concentration; BLG:AG ratio of 2:1) using small angle static light scattering (SALS). Acidification of BLG/AG dispersions was induced by dissolution of 0.11 wt% glucono-δ-lactone, allowing in situ SALS measurements. Time evolution of turbidity, scattered light intensity at 46° scattering angle ( I 46 ) or slope of scattering functions at high q range revealed the existence of six pH-induced structural transitions. During BLG/AG complexation and before coacervation took place, scattering profiles displayed a monotonic decrease of I ( q ) as a function of q. A correlation peak in the scattering functions was only observed when coacervates appeared in the system. The wave vector q max corresponding to the maximum in scattered intensity first shifted toward larger q values, indicating an increasing number of coacervates, then shifted toward smaller q values, as a consequence of the system coarsening. The power laws q max ∼ t − α and I max ∼ t − β gave values of 1.9 and 9.2, respectively, values much larger than those expected for intermediate and late stages of spinodal decomposition. From these results, it was concluded that complex coacervation between BLG and AG was a nucleation and growth type process. In addition, the temporal evolution of I 46 followed power laws with two different exponents. First exponent corresponding to BLG/AG complexation was 3.0 ± 0.3 and indicated a diffusion-controlled growth mechanism. Second exponent corresponding to the initiation of phase separation to the coacervation process was 6.5 ± 0.3 and revealed an interfacially-controlled growth mechanism.Exponent γ of the power law I ( q ) ∼ q − γ in the high q region obtained by small angle static light scattering on acidified BLG/AG dispersions at 0.1 wt% total biopolymer concentration and BLG:AG weight ratio of 2:1. Main structural transitions and corresponding pH are indicated in the figure. The shape of γ vs pH curve is the signature of complexation/coacervation between proteins and polysaccharides.
Keywords: Proteins; Polysaccharides; Gum arabic; Light scattering; Demixing; Coacervates;
Micellization of CTAB in the presence of silicate anions and the exchange between bromide and silicate at the micelle surface: A step to understand the formation of mesoporous molecular sieves at extremely low surfactant and silicate concentrations by Carolina Vautier-Giongo; Heloise O. Pastore (874-882).
The effect of silicate anions, from dilute aqueous tetramethylammonium silicate (TMASi) solutions (0–3.0 mmol L−1 in silicon), on the formation of hexadecyltrimethylammonium bromide (CTAB) micelles was investigated by means of a series of simple conductivity experiments. These two compounds are used in the preparation of mesoporous silicate molecular sieves. An increase in the monovalent silicate anion concentration decreases the critical micelle concentration (cmc) of CTAB, as might be expected from the decreased repulsive forces between the polar heads of the surfactant molecules. However, the decrease in cmc values is less pronounced than that observed in the presence of bromide ions, suggesting that Br− binds more strongly than Si(OH)3O− at the micelle surface. Through the ion-exchange formalism, a selectivity coefficient for Si(OH)3O−/Br− exchange of 0.30 ± 0.03 was estimated from the conductivity data. This value compares well with that of 0.4 ± 0.1 also determined in this work by the pyrene fluorescence quenching method. The experimental results were used to rationalize the formation of a surfactant supramolecular-templated mesoporous molecular sieve at extremely low surfactant (0.63 mmol L−1) and silicate (4.00 mmol L−1) concentrations.
Keywords: Mesoporous molecular sieves; CTAB; Micellization; Surfactant; Silicate;
Structural organization of cetyltrimethylammonium sulfate in aqueous solution: The effect of Na2SO4 by Eloi Feitosa; Marcelo Rodrigo Savério Brazolin; Rose Mary Zumstein Georgetto Naal; Maria Perpétua Freire de Morais Del Lama; Josias R. Lopes; Watson Loh; Marilena Vasilescu (883-889).
We used dynamic light scattering (DLS), steady-state fluorescence, time resolved fluorescence quenching (TRFQ), tensiometry, conductimetry, and isothermal titration calorimetry (ITC) to investigate the self-assembly of the cationic surfactant cetyltrimethylammonium sulfate (CTAS) in aqueous solution, which has SO2− 4 as divalent counterion. We obtained the critical micelle concentration (cmc), aggregation number ( N agg ) , area per monomer ( a 0 ) , hydrodynamic radius ( R H ) , and degree of counterion dissociation ( α ) of CTAS micelles in the absence and presence of up to 1 M Na2SO4 and at temperatures of 25 and 40 °C. Between 0.01 and 0.3 M salt the hydrodynamic radius of CTAS micelle R H ≈ 16 Å is roughly independent on Na2SO4 concentration; below and above this concentration range R H increases steeply with the salt concentration, indicating micelle structure transition, from spherical to rod-like structures. R H increases only slightly as temperature increases from 25 to 40 °C, and the cmc decreases initially very steeply with Na2SO4 concentration up to about 10 mM, and thereafter it is constant. The area per surfactant at the water/air interface, a 0 , initially increases steeply with Na2SO4 concentration, and then decreases above ca. 10 mM. Conductimetry gives α = 0.18 for the degree of counterion dissociation, and N agg obtained by fluorescence methods increases with surfactant concentration but it is roughly independent of up to 80 mM salt. The ITC data yield cmc of 0.22 mM in water, and the calculated enthalpy change of micelle formation, Δ H mic = 3.8 kJ mol −1 , Gibbs free energy of micellization of surfactant molecules, Δ G mic = − 38.0 kJ mol −1 and entropy T Δ S mic = 41.7 kJ mol −1 indicate that the formation of CTAS micelles is entropy-driven.The effect of Na2SO4 on the cmc and area per monomer at the water/air interface for CTAS micelles.
Keywords: Cationic surfactant; Micelle; Aggregation number; Surface tension; Dynamic light scattering; Steady-state fluorescence; Time resolved fluorescence; Conductimetry; Tensiometry; Isothermal titration calorimetry;
Aging of oil-in-water emulsions: The role of the oil by Holger Egger; Kathryn M. McGrath (890-899).
Controlling stability and aging of emulsions is important from commercial and scientific perspectives. Achieving such control comes through gaining an understanding of the relationship between emulsion constituents and microstructure and how these influence the kinetics and mechanism of destabilisation. We present here an investigation determining the rate of destabilisation as a function of time for a series of water/n-alkane/Triton X-100 oil-in-water emulsions. The time dependence of the emulsions was investigated using static light scattering, PFG-NMR and measurement of gross phase separation. By changing the chain length of the oil from hexane to tetradecane, an almost five orders of magnitude variation in emulsion lifetime could be achieved, while maintaining most of the other chemical and physical characteristics of the emulsions. Further, we show that while Ostwald ripening is the dominant destabilisation mechanism, two distinct regimes are evident. Initially, we observed an enhanced Ostwald ripening regime due to the presence of oil-swollen micelles in the aqueous continuum, that is a depletion flocculation mechanism is followed. The presence of oil-swollen micelles was confirmed using PFG-NMR. The micelles aid the gross oil transport between the discrete oil domains. Upon phase separation the oil-swollen micelles are predominantly removed from the emulsion along with the excess water resulting in a concomitant reduction in the ripening rate, producing the more general Ostwald ripening cubic dependence of droplet radius as a function of time for the lower molecular weight oils. The oils with higher molecular weight (decane and above), however, were observed to switch over to destabilisation via creaming. PFG-NMR was shown to be a powerful technique to fully probe emulsion microstructure as a function of time with droplet size and spacing being directly obtained from the data.SLS and PFG-NMR have been used to obtain full time dependence behaviour for a series of oil-in-water emulsions. Two different destabilisation mechanisms are followed in a given sample as a function of time.
Keywords: Oil-in-water emulsions; PFG-NMR; Destabilisation mechanisms; Ostwald ripening; Creaming;
Fully dilutable microemulsions embedded with phospholipids and stabilized by short-chain organic acids and polyols by Aviram Spernath; Abraham Aserin; Nissim Garti (900-909).
Evidence on the role of phosphatidylcholine (PC) as a membrane permeability enhancer was the driving force in forming new liquid nanosized (modified microemulsions) oral delivery system containing PC molecules. In this study we have demonstrated the feasibility of constructing phase diagrams with a large isotropic regions capable of being fully diluted with water. The microemulsions were stabilized with mixtures composed of PC and nonionic surfactant (polyoxyethylene-40 hydrogenated castor oil, HECO40) and short-chain organic acid as cosurfactant/cosolvent. When propionic acid served as the cosurfactant/cosolvent, the isotropic region was at its maximum (ca. 72% of the total phase diagram area). The presence of a blend of PC and HECO40 seems to have synergistic effects, forming an isotropic region comprising 72% of the area of the phase diagram, in comparison to 20 and 50% in systems stabilized by PC and HECO40, alone, respectively. The role of the PC molecules in the formation of those microemulsions is demonstrated by comparing three soy lecithins. Lecithin with a high PC content forms larger isotropic regions with more “free dilution” lines. Several nonionic surfactants have been investigated, yet only HECO40 seems to have a packing parameter suitable for the formation of large isotropic U-type systems.The paper stresses the use of bioavailability enhancers (phosphatidylcholine) and short organic acids to facilitate the formation of swollen reverse micelles that can be fully diluted by water to invert into o/w microemulsions.
Keywords: U-type microemulsions; Phosphatidylcholine; Lecithin; Phase behavior; Oral delivery; Permeability enhancer; Organic acids; Nonionic surfactant;
A phenol-induced structural transition in aqueous cetyltrimethylammonium bromide solution by J.P. Mata; V.K. Aswal; P.A. Hassan; P. Bahadur (910-915).
The effect of phenol on the structure of micellar solution of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) was investigated using viscosity, dynamic light scattering (DLS), small angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) techniques. The relative viscosity and apparent hydrodynamic diameters of the micelles in CTAB solution increase initially and then decrease with addition of phenol. SANS studies indicate a prolate ellipsoidal structure of the micelles. The axial ratio of the prolate ellipsoidal micelles increases and then decreases with addition of phenol, consistently with DLS and viscosity measurements. NMR studies confirm the solubilization of phenol to the palisade layer and growth of the micelles at high concentration of phenol as revealed from the broadening of peaks.Hydrodynamic diameters and diffusion coefficient for CTAB (50 mM) micelles at different concentration of phenol in water containing 0.01 M NaBr at 25 °C.
Keywords: Viscosity; DLS; SANS; Micellar transition;
Iso-branched semifluorinated alkanes in Langmuir monolayers by M. Broniatowski; P. Dynarowicz-Łątka (916-923).
A series of semifluorinated n-alkanes (SFAs), of the general formula: (CF3)2 ―CF―(CF2)6 ―(CH2) n H (in short iF9Hn), n = 11 – 20 have been synthesized and employed for Langmuir monolayer characterization. Surface pressure and electric surface potential measurements were performed in addition to Brewster angle microscopy results, which enabled both direct visualization of the monolayers structure and estimation of the monolayer thickness at different stages of compression. Our paper was aimed at investigating the influence of the iso-branching of the perfluorinated fragment of the SFA molecule on the surface behavior of these molecules at the air/water interface. It occurred that iF9 SFAs with the number of carbon atoms in the hydrogenated moiety from 11 to 20 are capable of Langmuir monolayer formation. Monolayers from iF9H11 to iF9H13 are instable, whereas those formed by iF9 SFAs with longer hydrogenated chains form stable films at the free surface of water. As compared to SFAs containing perfluorinated chain in a normal arrangement, iso-branched molecules have a greater tendency to aggregate. Lower stability of monolayers formed by iF9 SFAs as compared to F10 SFAs originated from the surface nucleation observed in BAM images, even at the very initial stages of compression. The dipole moment vector for iso-branched SFAs was found to be virtually aligned with the main axis of the molecule, contrary to F10 SFAs, where the dipole moment vector was calculated to be tilted with respect to the main molecular axis. Quantitative Brewster angle microscopy measurements (relative reflectivity experiments) enabled us to monitor the changes of monolayer thickness at different stages of monolayer compression.
Keywords: Langmuir monolayers; Air/water interface; Semifluorinated alkanes; Iso-branching; Surface potentials; Effective dipole moments; Brewster angle microscopy;
An ionic polymer bead-supported lipid system by M. Haratake; S. Hidaka; M. Ono; M. Nakayama (924-927).
In this paper, we report on the preparation of an ionic polymer bead-supported lipid system several hundred micrometers in diameter. The electrostatic attractive interactions between anionic lipids and cationic polymer beads served as a “molecular glue” to immobilize the lipids on the beads, and then the immobilized lipids prompted the spontaneous formation of lipid bilayer membranes. Confocal fluorescence microscopic techniques revealed that the lipid bilayer membranes were located along the outline of the beads. In addition, the integrity of the lipid bilayer membranes was microscopically confirmed by a low-molecular-weight dye (trypan blue) exclusion test.An ionic polymer bead-supported lipid system. Cationic polymer beads are tightly wrapped in closed lipids, in order not to permeate the trypan blue pigment molecules.
Keywords: Bilayer membrane; Immobilization; Ionic polymer; Lipid vesicle microbead;
Aggregation behavior in mixed system of double-chained anionic surfactant with single-chained nonionic surfactant in aqueous solution by Yanru Fan; Meiwen Cao; Guangcui Yuan; Yilin Wang; Haike Yan; Charles C. Han (928-937).
The aggregation behavior of mixed systems of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) or sodium bis(4-phenylbutyl) sulfosuccinate (SBPBS) with nonionic surfactant pentaethylene glycol mono-n-dodecyl ether (C12E5) have been studied by means of steady-state fluorescence, electrical conductivity, dynamic light scattering, transmission electron microscopy, electrophoretic light scattering and pyrene solubilization measurements. The critical concentrations for aggregation, micropolarity, mobility, solubilization capacity and morphology of aggregates are characterized. Two critical concentrations for aggregation are observed in the mixed surfactants, which may correspond to the formation of different kinds of aggregates. Moreover, it is more favorable for AOT–C12E5 to form mixed vesicles compared to SBPBS–C12E5 at higher mole fraction of C12E5. In addition, it is revealed that SBPBS–C12E5 mixture has larger solubilization capacity for pyrene than AOT–C12E5 system.
Keywords: Mixed vesicles; Mixed micelles; Critical concentrations for aggregation; Solubilization capacity; Double-chained surfactants; C12E5;
In situ formation of dispersed palladium nanoparticles in microemulsion: Efficient reaction system for ligand-free Heck reaction by Jian-Zhong Jiang; Chun Cai (938-943).
The ligand-free Heck reaction catalyzed by Pd(OAc)2 performed well in a TX10 oil-in-water microemulsion. TEM proved in situ formation distributed palladium nanoparticles in the microemulsion. The role of TX10 in the reaction system is the palladium nanoparticles reducing agent and stabilizer. The effect of reaction parameters on the Heck reaction conversion were discussed. The results indicated that the aqueous phase concentration, the base concentration, and the temperature played key roles in the conversion of the reaction. Iodobenzene was converted to the corresponding trans-stilbene quantitatively within 90–150 min. Therefore, the heptane/TX 10/butanol/water/propylene glycol microemulsion containing in situ formed palladium nanoparticles was a very efficient catalyst system for the ligand-free Heck reaction.
Keywords: Microemulsion; Heck reaction; Palladium;
Morphology of hybrid polystyrene-block-poly(ethylene oxide) micelles: Analytical ultracentrifugation and SANS studies by Lyudmila M. Bronstein; Irina A. Khotina; Dmitri M. Chernyshov; Peter M. Valetsky; Galina I. Timofeeva; Lidiya V. Dubrovina; Barry Stein; Robert Karlinsey; Alessandro Triolo; A. Weidenmann; F. Lo Celso; Roberto Triolo; Alexei R. Khokhlov (944-952).
Morphology and structure of aqueous block copolymer solutions based on polystyrene-block-poly(ethylene oxide) (PS-b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H2PtCl6⋅6H2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H2O was replaced with D2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H2PtCl6⋅6H2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS-b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D2O solutions, revealing good agreement of AUC and SANS data.
Keywords: Block copolymer; Surfactant; Hybrid micelles; Isotope effect;
Microenvironmental and conformational structure of triblock copolymers in aqueous solution by 1H and 13C NMR spectroscopy by Junhe Ma; Chen Guo; Yalin Tang; Jing Wang; Lily Zheng; Xiangfeng Liang; Shu Chen; Huizhou Liu (953-961).
1H and 13C nuclear magnetic resonance (NMR) spectra of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers in D2O solutions have been systematically investigated. The detailed assignments of various 1H and 13C NMR signals are presented. The hyperfine structure of PO ―CH2 ― protons was clearly assigned, the arising reason of this hyperfine structure was attributed to the influence of the chiral center of ―CHCH3 ― groups and the direct coupling between the PO ―CH2 ― and ―CH3 protons. The external standard 2,2-dimethyl-2-silapentane-5-sulfonate sodium salt (DSS) was firstly applied in this system. Accurate chemical shift values referenced to the external standard DSS were obtained. 1H NMR chemical shift of PO ―CH2 ― and ―CH3 signals shows a larger decrease in ppm values than that of EO ―CH2 ― signal with the increase of PPO/PEO ratio or temperature indicating that PO segments exist in a more hydrophobic microenvironment. A new resonance signal assigned to the PO ―CH2 ― protons appeared when the temperature is above the CMT, which is attributed to the breakdown of the intra-molecular (C―H)⋯O hydrogen bond between the PO ―CH2 ― protons and the ester oxygens. The breakdown of this intra-molecular hydrogen bond may result in a decrease of gauche conformers of the PPO chain. The increase of 13C NMR chemical shift of block copolymers validates this conformational change assumption. It can be inferred that the amount of gauche conformers decreases whereas that of trans conformers increases in both PO and EO chains when elevating the PPO/PEO ratio or temperature. The observed 13C NMR chemical shifts of PO segments show a bigger increase than those of EO segments, supporting the formation of a nonpolar microenvironment around PO segments.(a) One-dimensional original 1H NMR spectrum of 1% (w/v) Pluronic P105 at 20 °C in D2O solution. (b) EO ―CH2 ― and PO ―CH2 ― region ( 3.4 – 3.82 ppm ). (c) PO ―CH3 region ( 1.09 – 1.22 ppm ).
Keywords: PEO–PPO–PEO triblock copolymer; Microenvironment; Conformation; NMR;
On the viscosity of composite suspensions of aluminum and ammonium perchlorate particles dispersed in hydroxyl terminated polybutadiene—New empirical model by Reza Arefinia; Akbar Shojaei (962-971).
The rheological properties of fuel suspensions with various solid loadings up to close their maximum packing fraction and suspending media having different viscosities are investigated using the rotational viscometer at relatively low shear rates in which suspensions behave as Newtonian fluids. Aluminum (Al) and ammonium perchlorate (AP) particles are major solid components of any solid fuel system which should be distributed uniformly inside a polymeric binder based on hydroxyl terminated polybutadiene (HTPB). The experimental data generated in this investigation indicates that the relative viscosity of the suspensions is independent of viscosity of polymer binder, but in addition to solid content, geometrical aspects of the solid particles affect strongly the relative viscosity of suspensions. Maximum packing fraction of filler is found to be suitable quantitative measure of filler characteristics such as size, size distribution, shape and structure. Consequently, it is revealed that the relative viscosity of fuel suspension is a unique function of reduced volume fraction (Φ). Based on analogy of viscosity enhancement of reactive resin with cure conversion and suspension with filler content, an empirical model with two adjustable parameters originated from resin gelation model is suggested. According to this model and experimental results obtained in this investigation, a generalized model is proposed to describe the relative viscosity as a function of solid content in which the adjustable parameters are found to be general constants. The generalized model which is expressed as μ r = ( 1 − Φ ) 0.3 Φ − 2 is found to be quite accurate to predict the experimental data. Furthermore, the applicability and accuracy of the generalized model are evaluated using the viscosity data of some suspension systems reported in the literature.A new empirical generalized model to predict the relative viscosity of suspension systems is presented. The generalized model is as μ r = ( 1 − Φ ) 0.3 Φ − 2 in which Φ is the reduced volume fraction.
Keywords: Composites; Viscosity; Modeling; Suspension;
An improved method for determining zeta potential and pore conductivity of porous materials by Fuzhi Lu; Tuck Y. How; Daniel Y. Kwok (972-976).
An improved method based on streaming potential and streaming current was proposed to determine zeta potential and surface conductance of porous material simultaneously. In the electrokinetic generation mode, a resistor is connected to the generator and by measuring the voltage drop across resistors with different resistance, a true streaming current can be determined. The zeta potential and surface conductivity can be obtained simultaneously from their relation to streaming potential and streaming current. The electrode and ion concentration polarization effects during the measurement were also discussed. The resistance from channel ends to electrodes, which has typically been ignored in the literature, was shown to have a significant influence on the calculated zeta potential and surface conductance. Ignorance of this resistance would lead to underestimation of both zeta potential and surface conductance values.
Keywords: Zeta potential; Pore conductivity; Polarization effect;
Electrokinetic transport of a spherical gel-layer model particle: Inclusion of charge regulation and application to polystyrene sulfonate by Stuart Allison; Yao Xin (977-988).
An electrokinetic gel-layer model of a spherical, highly charged colloid particle developed previously [S. Allison, J. Colloid Interface Sci. 277 (2004) 248], is extended in several ways. The charge of the particle is assumed to arise from deprotonation of acidic groups that are present, in uniform concentration, over a portion (or all) of the gel layer. Free energy considerations coupled with Poisson–Boltzmann theory are used to estimate how the local electrostatic environment of a charged gel layer alters the local p K a of the acidic groups. This modulation of the charge of the colloidal particle, or “charge regulation,” can be significant even for colloidal particles with strongly acidic groups at moderate pH if the ambient salt concentration is low. The methodology is applied to the viscosity and electrophoretic mobility data of a particular polystyrene sulfonate latex over a broad range of monovalent salt (NaCl) concentration [M.J. Garcia-Salinas, F.J. de las Nieves, Langmuir 16 (2000) 715]. The experimental data can be accounted for by a gel layer model that decreases in thickness, but does not vanish, as the salt concentration is increased. Viscosity data provides valuable information about the degree of solvation of the colloidal particle and the thickness of the gel layer. The mobility data is best explained by a model in which only the outermost portion of the gel layer is charged. Charge regulation is significant at a monovalent salt concentration of 3 × 10 −3 mol / l and increases as the salt concentration decreases.
Keywords: Electrokinetic transport; Gel-layer modeling; Polystyrene sulfonate; Charge regulation;
Author Index for Volume 299 (989-991).