Journal of Colloid And Interface Science (v.298, #1)
Editorial Board (CO1).
Temperature effect on the zeta potential and fluoride adsorption at the α-Al2O3/aqueous solution interface by A. López Valdivieso; J.L. Reyes Bahena; S. Song; R. Herrera Urbina (1-5).
The effect of temperature and pH on the zeta potential of α-Al2O3 and adsorption of fluoride ions at the α-Al2O3/aqueous solution interface has been investigated through electrophoretic mobility measurements and adsorption studies, to delineate mechanisms involved in the removal of fluoride ions from water using alumina as adsorbent. When the temperature increases from 10 to 40 °C, the pH of the point of zero charge (pHpzc) shifts to smaller values, indicating proton desorption from the alumina surface. The pHpzc increases linearly with 1 / T , which allowed estimation of the standard enthalpy change for the surface-deprotonation process. Fluoride ion adsorption follows a Langmuir-type adsorption isotherm and is affected by the electric charge at the α-Al2O3/aqueous solution interface and the surface density of hydroxyl groups. Such adsorption occurs through an exchange between fluoride ions and surface-hydroxyl groups and it depends on temperature, pH, and initial fluoride ion concentration. At 25 and 40 °C, maximum fluoride adsorption density takes place between pH 5 and 6. Increasing the temperature from 25 to 40 °C lowers the adsorption density of fluoride.Fluoride ion adsorb at the α-Al2O3/aqueous solution interface following the Langmuir isotherm. Adsorption is high and maxima at pH 5 due to specific interaction of fluoride on AlOH+ 2 and AlOH surface sites and is low at pH 9 due to electrostatic repulsion between fluoride ions and the negative surface of alumina.
Keywords: Fluoride removal; Alumina; Electrokinetics; Adsorption; Water treatment; Fluorosis;
Removal of As(V) by Cu(II)-, Ni(II)-, or Co(II)-doped goethite samples by M. Mohapatra; S.K. Sahoo; S. Anand; R.P. Das (6-12).
The present study reports removal of As(V) by adsorption onto laboratory-prepared pure and Cu(II)-, Ni(II)-, and Co(II)-doped goethite samples. The X-ray diffraction patterns showed only goethite as the crystalline phase. Doping of ions in the goethite matrix resulted in shift of d-values. Various parameters chosen for adsorption were nature of adsorbent, percentage of doped cations in goethite matrix, contact time, solution pH, and percentage of adsorbate. It was observed that the pHpzc of the goethite surface depended on the nature and concentration of metal ions. The surface area as well as the loading capacity increased with the increase of dopant percentage in goethite matrix. A maximum loading capacity of 19.55 mg/g was observed for 2.7% Cu(II)-doped goethite. The adsorption kinetics for Ni(II), Co(II) and for undoped goethite attained a quasi-equilibrium state after 30 min with almost negligible adsorption beyond this time. In case of Cu(II)-doped goethite samples, the quasi-equilibrium state for As(V) adsorption was observed after 60 min. At each studied pH condition, it was observed that the percentage of adsorption of As(V) decreased in the order Cu(II)-doped goethite ⩾ Ni(II)-doped goethite > Co(II)-doped goethite > pure goethite. The adsorption followed: Langmuir isotherm, indicating monolayer formation.As(V) adsorption increased with the increase in % of doped ion in goethite matrix. Initial adsorption kinetics were observed to be very fast and quasi-equilibrium seems to be achieved within 60 min. The loading capacities for Cu, Ni, Co (∼1%) doped and pure goethite samples were 16.94, 15.83, 14.01, and 11.4 mg/g, respectively, at pH 2.
Keywords: Adsorption; As(V) removal; Goethite; Doping; Heavy metal; Langmuir isotherm; pH;
Hydrodynamic thickness of petroleum oil adsorbed layers in the pores of reservoir rocks by Saad F. Alkafeef; Meshal K. Algharaib; Abdullah F. Alajmi (13-19).
The hydrodynamic thickness δ of adsorbed petroleum (crude) oil layers into the pores of sandstone rocks, through which the liquid flows, has been studied by Poiseuille's flow law and the evolution of (electrical) streaming current. The adsorption of petroleum oil is accompanied by a numerical reduction in the (negative) surface potential of the pore walls, eventually stabilizing at a small positive potential, attributed to the oil macromolecules themselves. After increasing to around 30% of the pore radius, the adsorbed layer thickness δ stopped growing either with time or with concentrations of asphaltene in the flowing liquid. The adsorption thickness is confirmed with the blockage value of the rock pores' area determined by the combination of streaming current and streaming potential measurements. This behavior is attributed to the effect on the disjoining pressure across the adsorbed layer, as described by Derjaguin and Churaev, of which the polymolecular adsorption films lose their stability long before their thickness has approached the radius of the rock pore.After increasing to around 30% of the pore radius, the adsorbed layers thickness δ stopped growing either with time or with concentrations of asphaltene in the flowing liquid.
Keywords: Hydrodynamic thickness; Electrokinetic measurements; Streaming current; Streaming potential; Zeta potential; Disjoining pressure; Asphaltene; Permeability; Porous medium;
A multi-scale assessment of Pb(II) sorption on dolomite by Shinwoo Lee; James A. Dyer; Donald L. Sparks; Noel C. Scrivner; Evert J. Elzinga (20-30).
Macroscopic sorption studies indicated that Pb sorption capacity was independent of pH over the pH range 5–7, while sorption as a function of reaction time up to two weeks for systems with no bulk precipitate phases showed continuous Pb uptake on dolomite. This could be due to diffusion of Pb into the micropores of dolomite as well as an increase in surface sites caused by particle size reduction during suspension mixing. Normalized XANES spectra for systems undersaturated with respect to Pb carbonate precipitates resembled the spectrum of Pb4(OH)4+ 4, suggesting that Pb is mainly coordinated to dolomite as an inner-sphere surface complex. On the other hand, the XANES spectrum for 10−3 M Pb at 1 atm CO2(g) in a 2 M Mg(NO3)2 background electrolyte solution resembled that of cerussite, while a sample at 5 × 10 −4 M Pb in equilibrium with air and 2 M Mg(NO3)2 resembled that of hydrocerussite. EXAFS analyses of sorption samples in chloride solutions showed that there were only first-shell contributions under 1 atm CO2(g), while higher shell contributions from Ca/Mg were seen at 10−3.42 atm CO2(g). On the other hand, EXAFS samples prepared in nitrate solutions showed noticeable differences in speciation under different reaction conditions—from outer-sphere surface complexes at low Pb concentrations and pH, to inner-sphere surface complexes at moderate Pb concentrations and neutral pH, to the formation of Pb carbonate precipitates at the highest Pb loadings.
Keywords: Pb; Sorption; Dolomite; Underground injection; EXAFS; XANES; XPS;
Polymer density functional theory approach based on scaling second-order direct correlation function by Shiqi Zhou (31-38).
A second-order direct correlation function (DCF) from solving the polymer-RISM integral equation is scaled up or down by an equation of state for bulk polymer, the resultant scaling second-order DCF is in better agreement with corresponding simulation results than the un-scaling second-order DCF. When the scaling second-order DCF is imported into a recently proposed LTDFA-based polymer DFT approach, an originally associated adjustable but mathematically meaningless parameter now becomes mathematically meaningful, i.e., the numerical value lies now between 0 and 1. When the adjustable parameter-free version of the LTDFA is used instead of the LTDFA, i.e., the adjustable parameter is fixed at 0.5, the resultant parameter-free version of the scaling LTDFA-based polymer DFT is also in good agreement with the corresponding simulation data for density profiles. The parameter-free version of the scaling LTDFA-based polymer DFT is employed to investigate the density profiles of a freely jointed tangent hard sphere chain near a variable sized central hard sphere, again the predictions reproduce accurately the simulational results. Importance of the present adjustable parameter-free version lies in its combination with a recently proposed universal theoretical way, in the resultant formalism, the contact theorem is still met by the adjustable parameter associated with the theoretical way.The reduced site packing fraction profile G ( z ) = ρ ( z ) ( π / 6 ) / η ave with η ave = π 6 ∫ 0 H σ ρ ( z ) d z / H σ for a coexistence bulk state point of a 20-mers with η = ρ b σ 3 π 6 = 0.2 and H = 16 σ . The symbols are for simulation data [S. Zhou, J. Chem. Phys. (2005), submitted for publication].
Keywords: Surface; Adsorption;
Characteristics of phenol and chlorinated phenols sorption onto surfactant-modified bentonite by Zahir Rawajfih; Najwa Nsour (39-49).
Surfactant-modified bentonite was synthesized by replacing adsorbed Na+ with long-chain alkyl quaternary ammonium cation, hexadecyltrimethylammonium bromide (HDTMAB). The sorption isotherms of phenol, p-chlorophenol, and 2,4-dichlorophenol were modeled according to the Langmuir and Freundlich equations. The Langmuir isotherm was found to describe the equilibrium adsorption data well. The mechanisms and characteristics of sorption of these ionizable organic contaminants onto surfactant-modified bentonite from water were investigated systematically and described quantitatively. The sorption properties are affected by the treatment conditions, such as amount of organobentonite, and the properties of organic compounds. Results indicated that adsorption of phenols from water was in proportion to their hydrophobicities, which increased with chlorine addition (phenol<p-chlorophenol < 2,4-dichlorophenol). Sorption isotherms of these phenols were typically nonlinear. Both adsorption and partition contribute to the sorption of investigated phenols to organobentonite. The separate contributions of adsorption and partition to the total sorption of these compounds to organobentonite is analyzed mathematically. Results indicate that the partition effect is weak and linear with contaminant concentration, whereas the adsorption effect is more powerful and nonlinear with contaminant concentration. The sorption of phenols onto organobentonite was dominated by adsorption at low concentrations and partition started to dominate at high concentrations, making the organobentonites powerful sorbents for organic contaminants over a wide range of concentrations.Adsorption of phenol, p-chlorophenol, and 2,4-dichlorophenol by Jordanian organobentonite as a function of mineral concentration is proportional to their hydrophobicities, which increases with chlorine addition (phenol<p-chlorophenol < 2,4-dichlorophenol).
Keywords: Adsorption; Chlorinated phenols; Phenol; Partitioning; Sorption; Surfactant-modified clay;
Extended DLVO interactions between spherical particles and rough surfaces by Eric M.V. Hoek; Gaurav K. Agarwal (50-58).
An “extended DLVO” approach that includes Lifshitz–van der Waals, Lewis acid–base, and electrostatic double layer interactions is used to describe interaction energies between spherical particles and rough surfaces. Favorable, unfavorable, and intermediate deposition conditions are simulated using surface properties representing common aquatic colloids and polymeric membranes. The surface element integration (SEI) technique and Derjaguin's integration method are employed to calculate interaction energy. Numerical simulations using SEI demonstrate that nanometer scale surface roughness features can produce a distribution of interaction energy profiles. Local interaction energies are statistically analyzed to define representative interaction energy profiles—minimum, average, and maximum—for various combinations of simulated particles and surfaces. In all cases, the magnitude of the average interaction energy profile is reduced, but the reduction of energy depends on particle size, asperity size, and density of asperities. In some cases, a surface that is on average unfavorable for deposition (repulsive) may possess locally favorable (attractive) sites solely due to nanoscale surface roughness. A weighted average of the analytical sphere–sphere and sphere–plate expressions of Derjaguin reasonably approximates the average interaction energy profiles predicted by the SEI model, where the weighting factor is based on the fraction of interactions involving asperities.Extended DLVO interactions between nanoparticles and surfaces with nanoscale roughness features are modeled.
Keywords: DLVO theory; Particle deposition; Surface roughness; Surface element integration; Derjaguin; Membranes;
Formation of polyelectrolyte multilayers from polysaccharides at low ionic strength by Tsetska Radeva; Kamelia Kamburova; Ivana Petkanchin (59-65).
Layer-by-layer deposition of sodium carboxymethylcellulose (NaCMC) and chitosan (CHI) was used to create polyelectrolyte multilayers on ellipsoidal β-FeOOH particles at low ionic strength. Using electro-optics, we investigated the formation of films in dependence on the polyelectrolyte charge density by controlling pH of the dipping solutions. We found out a linear growth of the CMC/CHI films when they are constructed from highly charged CHI (at pH 4.0) and weakly charged NaCMC (at pH 4.0 and 5.5). The hydrodynamic thickness of the film constructed at pH 4.0/4.0 is unusually large for a linearly growing film (ca. 220 nm after deposition of 8 bilayers), but it strongly decreases (ca. 4 times) with increasing ionization of NaCMC (at pH 5.5). In both cases, the multilayer buildup proceeded through a series of adsorption–desorption steps. This was explained by a partial loss of CHI from the film surface on exposure to the solution of longer NaCMC molecules. The irregular film growth correlated quite well with the variations in the electrical polarizability of the polymer-coated particles. This correlation enabled us to conclude that the adsorption of both polymers occurs only on the film surface, with no diffusion in and out of the film bulk during deposition of each CMC/CHI bilayer.
Keywords: Polyelectrolyte multilayers; Polyssacharide multilayers; Multilayers from weak polyelectrolytes; Electro-optics of multilayers; Multilayers on colloidal particles;
Corrected thermodynamic description of adsorption via formalism of the theory of volume filling of micropores by Artur P. Terzyk; Piotr A. Gauden; Gerhard Rychlicki (66-73).
Based on the series of benzene adsorption and related enthalpy of adsorption data measured on porous carbons that possess various porous structures, we show that the creation of a solidlike structure in pores depends on the average pore diameter of an adsorbent. Taking into account the solidlike adsorbed phase in the thermodynamic description of the adsorption process via the formalism of the theory of volume filling of micropores (TVFM) leads to very good agreement between the data measured experimentally and those calculated from TVFM. Finally we show that the boundary between solidlike and liquidlike structures of benzene molecules in carbon pores is located around the average pore diameter, close to ca. 2.1–2.4 nm.
Keywords: Adsorption; Activated carbon; Porosity; Theory of volume filling of micropores; Thermodynamics;
Measurement of cation binding to immobilized vanillin by isothermal calorimetry by Eunice F.S. Vieira; Antonio R. Cestari; Elias B. de Santos; Cristiane X. Rezende (74-78).
Isothermal calorimetry was used to determine enthalpy changes for interaction of divalent cobalt, nickel, copper, and zinc chlorides with silica gel functionalized with vanillin, Sil―Van. The thermal effect, Q int , and the corresponding amount of cation that interacts, n int , were obtained in the same experiment. Langmuir expressions for adsorption isotherms were applied to determine the maximum adsorption capacity to form a monolayer, N mon , and the energy of interaction for a saturated monolayer per gram of Sil―Van, Q mon . From knowledge of N mon and Q mon , the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of Sil―Van, Δ mon H m , was determined. Interactions between the Lewis-acidic cations and the donor atom attached to silica are reflected by Δ mon H m values in the order Ni2+ > Cu2+ > Zn2+ ≅ Co2+.Isothermal calorimetry was used to evaluate energetics of adsorption of divalent cations on silica–vanillin (Sil―Van) at 25 °C and pH 6.0. Interactions between the Lewis-acidic cations and the donor atom attached to Sil―Van are reflected by Δ mon H m values in the order Ni2+ > Cu2+ > Zn2+ ≅ Co2+.
Keywords: Isothermal calorimetry; Adsorption of cations; Vanillin; Silica gel;
Studies on the interaction of some azo dyes (naphthol red-J and direct orange) with nontronite mineral by Vinod K. Gupta; Dinesh Mohan; Vipin K. Saini (79-86).
The adsorption of two azo dyes, namely naphthol red-J and direct orange, on nontronite mineral was studied as a function of pH and temperature. All the sorption studies were conducted in batch mode. The Langmuir and Freundlich isotherm models were applied. The isotherms are Langmuirian in nature, while the Freundlich equation is only valid over the low concentration range. The adsorption of the two dyes increases with increased temperature and decreases with increased pH. The data have been explained in terms of the area of contact of the dye molecule on the clay platelet vis-à-vis the area per anion exchange site. Estimated area per anion exchange site of the mineral and area associated per anionic dye molecule at nontronite surface was 642 and 454 Å2 for naphthol red-J and 642 and 440 Å2 for direct orange respectively. This has been further supported by X-ray measurements. Thermodynamic parameters of the process were evaluated.Effect of pH on the adsorption spectra of naphthol red-J.
Keywords: Adsorption; Azo dyes; Clays; Nontronite mineral;
Coating of zinc ferrite particles with a conducting polymer, polyaniline by Jaroslav Stejskal; Miroslava Trchová; Jitka Brodinová; Petr Kalenda; Svetlana V. Fedorova; Jan Prokeš; Josef Zemek (87-93).
Particles of zinc ferrite, ZnO⋅Fe2O3, were coated with polyaniline (PANI) phosphate during the in situ polymerization of aniline in an aqueous solution of phosphoric acid. The PANI–ferrite composites were characterized by FTIR spectroscopy. X-ray photoelectron spectroscopy was used to determine the degree of coating with a conducting polymer. Even a low content of PANI, 1.4 wt%, resulted in the 45% coating of the particles' surface. On the other hand, even at high PANI content, the coating of ferrite surface did not exceeded 90%. This is explained by the clustering of hydrophobic aniline oligomers at the hydrophilic ferrite surface and the consequent irregular PANI coating. The conductivity increased from 2 × 10 −9 to 6.5 S cm−1 with increasing fraction of PANI phosphate in the composite. The percolation threshold was located at 3–4 vol% of the conducting component. In the absence of any acid, a conducting product, 1.4 × 10 −2 S cm −1 , was also obtained. As the concentration of phosphoric acid increased to 3 M, the conductivity of the composites reached 1.8 S cm−1 at 10–14 wt% of PANI. The ferrite alone can act as an oxidant for aniline; a product having a conductivity 0.11 S cm−1 was obtained after a one-month immersion of ferrite in an acidic solution of aniline.Particles of zinc ferrite, ZnO⋅Fe2O3, were coated with polyaniline (PANI) phosphate during the in situ polymerization of aniline in an aqueous solution of phosphoric acid. The PANI–ferrite composites were characterized by FTIR spectroscopy.
Keywords: Conductivity; Conducting polymer; Ferrite; FTIR spectra; Percolation; Polyaniline; Surface coating;
The role of few-asperity contacts in adhesion by E.J. Thoreson; J. Martin; N.A. Burnham (94-101).
The surface roughness of a few asperities and their influence on the work of adhesion is of scientific interest. Macroscale and nanoscale adhesion data have seemingly given inconsistent results. Despite the importance of bridging the gap between the two regimes, little experimental work has been done, presumably due to the difficulty of the experiment needed to determine how small amounts of surface roughness might influence adhesion data lying in between the two scales. To investigate the role of few-asperity contacts in adhesion, the pull-off force was measured between different sized atomic-force microscope (AFM) tips (with different roughnesses) and sample surfaces that had well-controlled material properties. There were seventeen tips of four different types, with radii from 200 nm to 60 μm. The samples were unpatterned single crystal silicon with a chemical silicon dioxide surface resulting from a standard silicon wafer clean. Some of the samples were treated with a few angstroms of vapor deposited diphenylsiloxane. We observed that the uncorrected (for surface roughness) pull-off force was independent of the radius of the AFM tip, which was contrary to all continuum-mechanics model predictions. To explain this behavior, we assumed that the interactions between the AFM tip and sample were additive, material properties were constant, and that the AFM tip, asperities, and sample surfaces were of uniform density. Based on these assumptions, we calculated a simple correction due to the measured root mean square (RMS) surface roughness of the AFM tips. The simple correction for the RMS surface roughness resulted in the expected dependence of the pull-off force on radius, but the magnitudes were higher than expected. Commercial and heat-treated AFM tips have minimal surface roughness and result in magnitudes that are more reliable. The relative uncertainty for the pull-off force was estimated to be 10%. In this paper, we derive how the cantilever and tip parameters contribute to the measured pull-off force and show how the corrected results compare with theory. Although much work is still needed, the work presented here should advance the understanding of adhesion between the macroscale and nanoscale regimes.Pull-off force between silicon die and AFM tips. (Left) The pull-off force corrected for the angle of repose. (Right) Pull-off force corrected for both angle of repose and surface roughness.
Keywords: Surface roughness; Surface forces; Van der Waals forces; Particle deposition; Work of adhesion; AFM; Adhesion; Silicon dioxide;
Novel amphiphilic macromolecules and their in vitro characterization as stabilized micellar drug delivery systems by Li Tao; Kathryn E. Uhrich (102-110).
A series of amphiphilic macromolecules, amphiphilic scorpion-like macromolecules (AScMs) and amphiphilic star-like macromolecules (ASMs), were evaluated as potential drug delivery systems for intravenous administration. AScMs aggregate to form polymeric micelles; whereas the ASMs have a covalently bound core structure and behave as unimolecular micelles. Four structurally different AScMs and two ASMs were selected for further evaluation focusing on micellar stability and biocompatibility. AScMs were determined to have extremely low cmc values, indicating excellent thermodynamic stability compared to other polymeric micelle systems. Particle sizes of the AScM polymeric micelles and ASM unimolecular micelles were between 10 and 20 nm, and remained constant for up to 3 weeks storages as aqueous solutions at room temperature (∼23 °C) and 37 °C. The dissociation kinetics of the AScM polymeric micelles were slowed relative to small molecule surfactant micelles, again indicating enhanced kinetic stability. With respect to hemolytic activity, AScMs with longer acyl chains were hemolytic; whereas the ASMs had minimal hemolytic activity due to the covalently bound structure. Both ASM unimolecular micelles and AScM polymeric micelles have excellent micellar stability, but the ASMs are more suitable as injectable drug delivery systems due to their low hemolytic activity.
Keywords: Amphiphilic macromolecules; ASM; AScM; Polymeric micelle; Unimolecular micelle; Thermodynamic stability; Storage stability; Hemolytic activity;
Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites by B.C. Ray (111-117).
Weight change behavior of fiber-reinforced polymer composites in humid and thermal environments appears to be a complex phenomena. The state of fiber/matrix interface is believed to influence the nature of diffusion modes. A significant weakening often appears at the interface during the hygrothermal ageing. It effects the moisture uptake kinetics and also the reduction of mechanical properties. The importance of temperature at the time of conditioning plays an important role in environmental degradation of such composite materials. An attempt has been made here to evaluate the deleterious effect of temperature on shear strength of carbon/epoxy and glass/epoxy composites during hygrothermal conditionings. Mechanical tests were conducted at room temperature to assess the effectiveness of the relaxation process in the nullification of environmentally-induced damage in the composites.The study reveals that the fiber/matrix adhesive damage and a loss of interfacial integrity are dominating mechanisms in polymer composites during environmental ageing.
Keywords: Polymer composites; Adhesion; Diffusion; Interfaces; Ageing; Mechanical properties;
pH-responsive, self-assembling nanoparticle from a fullerene-tagged poly(l-glutamic acid) and its superoxide dismutase mimetic property by Nobuyuki Higashi; Takeshi Shosu; Tomoyuki Koga; Masazo Niwa; Toru Tanigawa (118-123).
In this study, we describe the fabrication of novel fullerene-containing peptide-nanoparticles through self-assembly. A water-soluble, poly(l-glutamic acid)-attached fullerene was newly synthesized and the conformation and self-assembling property in water were examined by using circular dichroism, FTIR, UV, atomic force microscopy, and dynamic light scattering measurements. In the lower pH region (<6.8), the fullerene peptide self-assembles into nanoparticles that are ca. 100–200 nm in diameter. These nanoparticles are rich in α-helices, and stacking interaction of fullerene moieties contributes to the stability of the high-order structure. In addition, these particle sizes can be easily controlled by changing pH that results in causing the conformational transition of PLGA segment. Finally, the fullerene-containing nanoparticle is confirmed to be capable of removing the biologically important superoxide radical in comparison with the superoxide dismutase.A pH-responsive, self-organized nanoparticle was successfully constructed by using a conformational transition of the polypeptide segment and tagging fullerene at one chain end. The resultant nanoparticle was confirmed to be capable of removing the biologically important superoxide radical.
Keywords: Peptides; Conformation; Fullerene; Nanoparticle; Self-assembly; Superoxide dismutase mimetic;
Adsorption of novel thermosensitive graft-copolymers: Core–shell particles prepared by polyelectrolyte multilayer self-assembly by Mihaela Rusu; Dirk Kuckling; Helmuth Möhwald; Monika Schönhoff (124-131).
The adsorption properties of thermosensitive graft-copolymers are investigated with the aim of developing self-assembled multilayers from these copolymers. The copolymers consist of a thermoreversible main chain of poly(N-isopropylacrylamid) and a weak polyelectrolyte, poly(2-vinylpyridine), as grafted side chains. ζ-Potential, single particle light scattering and adsorption isotherms monitor the adsorption of the thermoreversible copolymers to precoated colloidal particles. The results show a smaller surface coverage for a larger density of grafted chains. The surface coverage is discussed in terms of surface charge density in the adsorbed monolayer. Taking into account the monolayer adsorption properties, conditions are developed for the multilayer formation from these copolymers. A low pH provides a sufficient charge density of the grafted chains to achieve a surface charge reversal of the colloids upon adsorption. The charge reversal after each adsorbed layer is monitored by ζ-potential and the increase of the thickness is determined by light scattering. Stable and reproducible multilayers are obtained. The results imply that the conformation of the thermosensitive component in multilayers depends strongly on the grafting density, where the polymer with a higher grafting density adsorbs in a flat conformation while that with a lower grafting density adsorbs with more loops.Multilayer formation from thermosensitive graft-copolymers on colloidal templates is demonstrated by the reversal of the ζ-potential after each layer.
Keywords: Polyelectrolyte; Layer-by-layer; Self-assembly; Multilayer; Thermosensitive; Thermoreversible; Colloid; ζ-Potential; Adsorption isotherm; Poly(N-isopropylacrylamid);
Adsorption-induced fibronectin aggregation and fibrillogenesis by Delphine Pellenc; Hugues Berry; Olivier Gallet (132-144).
Fibronectin (Fn), a high molecular weight glycoprotein, is a central element of extracellular matrix architecture that is involved in several fundamental cell processes. In the context of bone biology, little is known about the influence of the mineral surface on fibronectin supramolecular assembly. We investigate fibronectin morphological properties induced by its adsorption onto a model mineral matrix of hydroxyapatite (HA). Fibronectin adsorption onto HA spontaneously induces its aggregation and fibrillation. In some cases, fibronectin fibrils are even found connected into a dense network that is close to the matrix synthesized by cultured cells. Fibronectin adsorption-induced self-assembly is a time-dependant process that is sensitive to bulk concentration. The N-terminal domain of the protein, known to be implicated in its self-association, does not significantly inhibit the protein self-assembly while increasing ionic strength in the bulk alters both aggregation and fibrillation. The addition of a non-ionic surfactant during adsorption tends to promote aggregation with respect to fibrillation. Ultimately, fibronectin fibrils appear to be partially structured like amyloid fibrils as shown by thioflavine T staining. Taken together, our results suggest that there might be more than one single organization route involved in fibronectin self-assembly onto hydroxyapatite. The underlying mechanisms are discussed with respect to Fn conformation, Fn/surface and Fn/Fn interactions, and a model of fibronectin fibrillogenesis onto hydroxyapatite is proposed.Adsorption onto hydroxyapatite induces fibronectin aggregation and fibrillogenesis. Fibronectin fibril formation increases with time and bulk concentration but exhibits a non-monotonic dependence on the ionic strength in the bulk.
Keywords: Fibronectin; Aggregation; Fibrillogenesis; Protein adsorption; Hydroxyapatite; Biomaterials;
Thermodynamic characterization of the prevailing molecular interactions in mixed floating monolayers of phospholipids and usnic acid by Cesar A.S. Andrade; Nereide S. Santos-Magalhães; Celso P. de Melo (145-153).
The investigation of the characteristics of mixed floating monolayers of phospholipids and usnic acid (UA), an active metabolite from lichens, can provide valuable information on how to prepare stable liposomes that could serve as carriers of UA for therapeutic proposes. The present paper is concerned with the thermodynamic analysis of the behavior of Langmuir monolayers formed by mixing different phospholipids (dibehenoylphosphatidylcholine, DBPC, dipalmitoylphosphatidylcholine, DPPC, and dioleoylphosphatidylcholine, DOPC) and UA at varied molar fractions. Relevant thermodynamic parameters such as excess areas, excess free energies and free energy of mixing were derived from the surface pressure data obtained from compression measurements performed in a Langmuir trough. For the largest lateral pressure examined (25 mN/m), negative values of the excess free energy were found only for the DOPC/UA monolayer, which should be the most stable of them. Based on the calculated values of the free energy of mixing, we note that the DBPC/UA and DPPC/UA systems present the best mixed character at low pressures and when the molar fraction of the UA is 0.5; at that relative concentration and at low values of the external pressure, the UA molecules can better mix and interact with the phospholipid molecules. The compression isotherms for mixed monolayers show no visible transitions, exhibiting a more organized phase that corresponds to a negative free energy of mixing. We have established that the most stable monolayers were those corresponding to DOPC/UA mixtures with a UA molar fraction of 0.75.Negative values of Δ G M were found for DOPC/UA monolayers, in an indication of thermodynamic stability and that a favorable interaction exists between UA and the phospholipid in these films.
Keywords: Phospholipids; Usnic acid; Langmuir films; Thermodynamic analysis;
The characterisation of a novel, covalently modified, amphiphilic alginate derivative, which retains gelling and non-toxic properties by Eilish Broderick; Henry Lyons; Tony Pembroke; Hugh Byrne; Brian Murray; Michael Hall (154-161).
The characterisation of a novel amphiphilic material, Alg-C4, produced from butanol linked by esterification to alginate is presented. The novel derivative retains the gelling and non-toxic properties of native alginate. FTIR spectra of Alg-C4 contained the characteristic hydroxyl and carboxyl bands, but also featured additional peaks at 1736 and 1134 cm−1, indicating the presence of ester bonds. NMR studies showed the presence of butyl groups. The endothermic peak and exothermic peak present in the DSC thermogram of native alginate were also apparent in the Alg-C4 thermogram, but had shifted to lower temperatures (from 106 to 87 °C and from 254 to 247 °C, respectively). In addition, the exothermic peak was significantly reduced for Alg-C4 (5 mW compared to 20 mW in native alginate). Scanning electron microscopy was used to examine surface topography. The native alginate beads appeared smooth while Alg-C4 beads had a different, rougher appearance. Using circular dichroism it was found that the ratio of mannuronic to guluronic residues in the Alg-C4 was markedly increased compared to the native alginate (1.33 to 2.47), suggesting the preferential esterification of butanol to the guluronic residues. Exposure of ovarian granulosa cells in vitro to the Alg-C4 material demonstrated that granulosa cell viability (MTT test) was unchanged when compared to native alginate, which is regarded as non-toxic. The novel material is very stable, giving identical FTIR, DSC and gelling performance after 12 months storage at temperatures ranging from 10 to 20 °C. The data support the successful preparation of a stable modified alginate with characteristic hydrophilic properties and, in addition, a novel hydrophobic character.A novel, stable, amphiphilic alginate-butanol ester, retaining gelling ability and its non-toxic nature, is characterised by FTIR, DSC, CD, NMR and SEM.
Keywords: Alginate; Amphiphilic; DSC; FTIR; NMR; SEM; Circular dichroism; Cell culture;
Latex diffusion at high volume fractions studied by fluorescence microscopy by Gunilla Carlsson; Lars Järnström; Jan van Stam (162-171).
The behavior of fluorescent latex probes (radii 0.05, 0.1, and 0.5 μm) in latex host particle suspensions was investigated by fluorescence microscopy with image analysis. The volume fraction of the host latex was varied between 0 and 0.50. A careful statistical analysis was performed to examine the accuracy of the fluorescence microscopy method, from which the direct observation of the Brownian motion gives the diffusion coefficient. The method was found to meet all statistical requirements. From rheological measurements, the maximum volume fraction and the intrinsic viscosity can be obtained. The Krieger–Dougherty equation can be used for the prediction of sample viscosities. The predicted viscosities were used to obtain the theoretical diffusion coefficients with the Stoke–Einstein equation. When comparing the theoretical diffusion coefficients with the experimental ones, it turned out that all models tested yielded acceptable predictions of the diffusion coefficients.
Keywords: Fluorescence microscopy; Latex; Diffusion; High volume fractions; Viscosity;
Growth mechanism of ZnO nanocrystals with Zn-rich from dots to rods by Guiye Shan; Xinli Xiao; Xin Wang; Xianggui Kong; Yichun Liu (172-176).
ZnO nanocrystals from dot to rod were synthesized by simply changing Zn2+ concentration in ZnO seed solutions. The growth of ZnO nanocrystals was sensitive to the amount of Zn2+ in the solution. The growth process of ZnO from dot to rod was observed by optical spectra, transmission electron microscopy and X-ray diffraction spectra. From these results, the growth mechanism of ZnO from dots to rods was discussed.
Keywords: ZnO; Nanorods; Growth transition; Dipole interaction;
Preparation of platinum nanoparticles using star-block copolymer with a carboxylic core by Liwei Zhang; Haijun Niu; Yongming Chen; Hanfan Liu; Mingyuan Gao (177-182).
Well-defined star polymers containing a functionalized core supply a molecular nanocavity and may be used to control formation of inorganic nanoparticles. Herein, platinum (Pt) nanoparticles of 2–4 nm were prepared by using (poly(acrylic acid)-b-polystyrene)6 (PAA-b-PS)6 amphiphilic star block copolymer as a novel single molecular stabilizer. This PAA core functionalized star polymer was obtained by hydrolysis of (poly(tert-butyl acrylate)-b-polystyrene)6 (PtBA-b-PS)6, which was synthesized by sequential atom transfer radical polymerization (ATRP) of tert-butyl acrylate and styrene with an initiator bearing six 2-bromoisobutyloxyl groups. Pt(IV) ions were loaded by ion exchange to the core of the star polymer and Pt nanoparticle stabilized by single star polymer was produced by a reduction with NaBH4.
Keywords: Star-block copolymer; Platinum nanoparticles; Preparation; Unimolecular micelle;
Porous agglomerates in the general linear flow field by P. Vainshtein; M. Shapiro (183-191).
We calculate the flow within and around a porous spherical agglomerate suspended in the general linear flow field, and also the flow induced by its rotation. We use the Stokes equations exterior to the particle and the Brinkman equations inside it. The effect of particle permeability on the flow is expressed via the Brinkman parameter β = r 0 / k , where r 0 is particle radius and k is its permeability. With translational creeping motion of porous spheres in a quiet fluid investigated by Debye and Bueche [P. Debye, A.M. Bueche, J. Chem. Phys. 16 (6) (1943) 573–579], this study provides information necessary for investigating dynamics of porous particles moving in creeping shear flows under the action of external forces and torques. The agglomerate flow field solutions are used to calculate the effective viscosity of a dilute suspension of porous solid aggregates, which generalizes the well-known Einstein's equation for solid suspensions. The agglomerate effective viscosity diameter is proposed which allows using the Einstein's formula evaluation of the agglomerates suspension viscosity.The solutions for the flow fields within and around a porous agglomerate are used to calculate the moment on the rotating particle and the effective viscosity of a dilute suspension of porous solid aggregates. The latter generalizes the well-known Einstein's equation for solid suspensions.
Keywords: Agglomerate; Suspension; Viscosity;
Cross-condensation and particle growth in aqueous silane mixtures at low concentration by C. Heitz; G. Laurent; R. Briard; E. Barthel (192-201).
We have observed the condensation of a mixture of γ-glycidoxypropylmethyldiethoxysilane and 3-aminopropyltriethoxysilane in dilute aqueous solutions. NMR and IR spectroscopy have allowed to follow the condensation process in the mixture, which is noticeably enhanced and proceeds faster than for each silane on its own. Cross-condensation between the two silanes was evidenced. When the hydrophilic aminosilane is in excess, the condensation, as evidenced by dynamic light scattering, proceeds toward gel formation because the oligomers formed are essentially hydrophilic. When the more hydrophobic epoxysilane is in excess, oligomer growth proceeds slowly and results in a destabilization of the solution: due to their hydrophobic character, the oligomers formed coalesce suddenly into 200-nm-diameter aggregates. Coatings deposited from such solutions with high epoxysilane content can be used to strengthen glass. We show that the progress of condensation in solution results in a wetting transition during deposition of the silane film on glass by dip coating. The production of increasingly hydrophobic oligomers as the reaction time increases results in adsorption of more hydrophobic aggregates at the surface, which eventually leads to dewetting of the film: in the absence of film, glass strengthening disappears.Cross-condensation and particle growth in dilute aqueous silane mixtures containing a poorly water soluble difunctional epoxysilane and a very soluble trifunctional aminosilane.
Keywords: Aminosilane; Epoxysilane; Condensation; 29NMR spectroscopy; INEPT; Infrared spectroscopy; Dynamic light scattering; Particle; Wetting; Coating;
Microstructure control of iron hydroxide nanoparticles using surfactants with different molecular structures by Motoyuki Iijima; Yuichi Yonemochi; Mayumi Tsukada; Hidehiro Kamiya (202-208).
To control the morphology and crystal phase of iron oxide nanoparticles within several 10 nm in diameter, a microbial-derived surfactant (MDS) with a high carboxyl-group density and relatively low molecular weight (about 650 g/mol) or an artificially synthesized polyacrylic acid sodium salt (PAA) was added into the raw material aqueous solution before iron oxide particle synthesis by the gel–sol method. While pseudo-cubic hematite particles with a diameter of 500 nm were prepared without surfactant addition, spherical iron hydroxide nanoparticles with a diameter of 20 nm were prepared by MDS addition. In contrast, needle-type iron hydroxide nanoparticles with a length of 100 nm along the long axis were prepared by PAA addition. Complex formation due to the interaction between COO− groups in each surfactant and Fe3+ ions, as well as the template role prior to the synthesis of iron oxide in raw aqueous solution, inhibited the phase transition from iron hydroxide to hematite. Furthermore, the morphology of the iron hydroxide nanoparticles depended on the molecular structure of the surfactants.
Keywords: Hematite; Akageneite; Microbial-derived surfactants; Polyacrylic acid sodium salt; Template;
Colloidal aggregation phenomena: Spatial structuring of TEOS-derived silica aerogels by Ekaterina Vinogradova; Mirna Estrada; Abel Moreno (209-212).
In this contribution, the homogeneity of silica aerogels made from tetraethyl orthosilicate (TEOS) was studied by means of Fourier transform infrared (FTIR) and 29Si nuclear magnetic resonance (NMR) spectroscopies. FTIR spectra show a slight difference in the asymmetric Si–O–Si stretching vibration frequency in the outer and inner part of the aerogels. According to the 29Si NMR data, a higher relation Q 4 / Q 3 was obtained in the inner parts of the gels compared with their outer parts, proving the difference in the cross linkage of the silica network. The obtained results are interpreted in terms of the specific spatial structuring of the colloidal suspensions due to the presence of gravity.The homogeneity of silica aerogels made from tetraethyl orthosilicate (TEOS) was studied by means of Fourier transform infrared (FTIR) and 29Si nuclear magnetic resonance (NMR) spectroscopies. The obtained data show a difference in the compactness of the silica network in the outer and in the inner part of the prepared gels. We explain these phenomena in terms of the specific spatial structuring of the colloidal suspensions.
Keywords: Silica gel; TEOS; Hydrogels; Aerogels; Microgravity;
Electric forces induced by a charged colloid particle attached to the water–nonpolar fluid interface by Krassimir D. Danov; Peter A. Kralchevsky (213-231).
Here, we solve the problem about the electric field of a charged dielectric particle, which is adsorbed at the water–nonpolar fluid (oil, air) boundary. The solution of this problem is a necessary step for the theoretical prediction of the electrodipping force acting on such particle, as well as of the electrostatic repulsion and capillary attraction between two adsorbed particles. In accordance with the experimental observations, we consider the important case when the surface charges are located at the particle–nonpolar fluid boundary. To solve the electrostatic problem, the Mehler–Fock integral transform is applied. In the special case when the dielectric constants of the particle and the nonpolar fluid are equal, the solution is obtained in a closed analytical form. In the general case of different dielectric constants, the problem is reduced to the numerical solution of an integral equation, which is carried out by iterations. The long-range asymptotics of the solution indicates that two similar particles repel each other as dipoles, whose dipole moments are related to the particle radius, contact angle, dielectric constant and surface charge density. The investigated short-range asymptotics ensures accurate calculation of the electrodipping force. For a fast and convenient application of the obtained results, the derived physical dependencies are tabulated as functions of the contact angle and the dielectric constants.
Keywords: Colloid particles; Electric field of adsorbed particles; Electric-field-induced capillary attraction; Electrodipping force; Interactions between adsorbed charged particles; Particle-stabilized emulsions; Particulate monolayers;
Preparation of highly monodisperse poly(methyl methacrylate) particles incorporating fluorescent rhodamine 6G for colloidal crystals by Daisuke Nagao; Naoto Anzai; Yoshio Kobayashi; Shunchao Gu; Mikio Konno (232-237).
Soap-free emulsion polymerization was extended to preparation of monodisperse poly(methyl methacrylate) (PMMA) particles incorporating rhodamine 6G (R6G) fluorescent molecules. The polymerization was conducted in the presence of an anionic monomer, p-styrenesulfonate (NaSS), which improved dispersion stability of the polymer particles. NaSS concentrations was ranged up to 2 mol/m3 H2O in the polymerization at 0.5 kmol/m3 H2O methyl methacrylate (MMA) monomer and 5 mol/m3 H2O potassium persulfate (KPS) initiator for R6G concentrations from 0.1 to 10 mol/m3-polymer. At R6G concentrations lower than 1.0 mol/m3-polymer, PMMA particles were highly monodisperse and incorporated most R6G molecules. The average sizes of PMMA particles were in a rage of 160–300 nm, and decreased with the concentration of NaSS. The high monodispersity of the particles enabled the fabrication of colloidal crystals of the particles with a vertical deposition method.Highly monodisperse polymer particles could be prepared in soap-free emulsion polymerization of MMA in the presence of rhodamine 6G. The high monodispersity of particles enabled the fabrication of colloidal crystals.
Keywords: Fluorescent; Monodisperse; PMMA; Polymer particle; Rhodamine 6G; Soap-free emulsion polymerization; Anionic monomer; Dispersion stability; Colloidal crystal; Vertical deposition method;
Alumina interaction with AMPS–MPEG random copolymers III. Effect of PEG segment length on adsorption, electrokinetic and rheological behavior by H. Bouhamed; A. Magnin; S. Boufi (238-247).
The effect of different 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS)–methoxypolyethyleneglycol methacrylate (MPEG) comb-like copolymers on the adsorption behavior, electrokinetic and rheological properties of alumina suspensions has been investigated. The change in adsorption isotherms with the content of the two monomers, the medium pH and the ionic strength indicated that the interaction of these copolymers was found to be controlled by both the fraction of ionic groups on the polymer and by the length of the polyethyleneglycol (PEG) segments. Adsorption of the copolymers on alumina particles is accompanied by a shift in the IEP toward acid pH values and may lead to a charge reversal above a certain level. The presence of the PEG segment equally affects the magnitude of the zeta potential by moving the shear plane forward. Addition of the copolymers greatly affects the rheological behavior of the suspension; the viscosity at a defined shear rate decreases and reaches an optimum, which is all the lower as the fraction of the ionic groups is higher. The dispersing effect of the copolymer was controlled by both the ionization level of the copolymer and by the length of the PEG segments.Schematic illustration of the AMPS–MPEG comb-like copolymer at the surface of alumina particles in aqueous medium and over a pH range 4–9. The ionic (SO− 3) groups acts as an anchoring site whereas the PEG segments protrude from the surface toward the continuous medium.
Keywords: Adsorption; Copolymer; Stability; Rheology;
Effect of the ionic surfactant concentration on the stabilization/destabilization of polystyrene colloidal particles by Ana B. Jódar-Reyes; Antonio Martín-Rodríguez; Juan L. Ortega-Vinuesa (248-257).
One of the most interesting properties of the surfactants is that they are able to alter the stability of colloidal dispersions. Despite its great industrial relevance, only a few works analyze the colloidal stability of these systems at high surfactant concentrations (well above the critical micelle concentration (CMC)). In the present work, the colloidal stability of polystyrene particles is studied under a wide range of ionic surfactant concentrations. The effects of the surface charge of the latex particles (evaluating both sign and value), and surfactant type (cationic or anionic) have been examined. Colloidal stability data have been gathered by monitoring aggregation using a nephelometric technique. As will be shown, it is possible to reach different stability regimes using the same colloidal system just by changing the surfactant concentration. Independently of the sign of both the surfactant and the surface, the destabilization of the system consistently takes place above certain surfactant concentration due to a depletion effect from non-adsorbed micelles. This destabilization can be predicted by adding to the DLVO interaction energy a new contribution addressing the force between two spherical particles in the presence of non-adsorbing spherical macromolecules.
Keywords: Polystyrene particles; Colloidal stability; Ionic surfactants; Micelle depletion;
The controlling effect of pH on oxidation of Cr(III) by manganese oxide minerals by Xiong Han Feng; Li Mei Zhai; Wen Feng Tan; Wei Zhao; Fan Liu; Ji Zheng He (258-266).
Oxidation of Cr(III) by three types of manganese oxide minerals (birnessite I, birnessite II, and todorokite) and effects of pH were investigated by chemical analysis, equilibrium redox, X-ray diffraction (XRD), and transmission electron microscopy. The effects of pH in the reaction systems on the oxidation of Cr(III) were similar among the three manganese oxide minerals. As pH increased from pH 2.0, the amount of Cr(III) oxidized by the tested manganese oxide minerals first increased, and then peaked at pH 3.0–3.5. While pH continually increased from 3.0 to 3.5, the amount of Cr(III) oxidized by the manganese oxide minerals sharply decreased. Until pH was higher than 5.0–5.5, the Cr(III) oxidation amounts changed to a small extent or kept stable. pH influenced the oxidation of Cr(III) mainly by altering the redox potential in the system, i.e., the concentration of H+, the species of Cr(III), and their distributions in the system. However, the surface charge of the manganese oxide minerals, subjected to the pH in the system, was not found to greatly influence the extent of the oxidation. When pH was below 5.0, oxidation of Cr(III) by the manganese oxide minerals was (or tended to be) an equilibrium reaction and was controlled thermodynamically. When pH was above 5.0–5.5, Cr(OH)3 precipitate was produced in the system and pH had little effect on the oxidation content of Cr(III).pH effect on oxidation of Cr(III) by manganese oxide minerals was controlled by the redox potential when pH < 5 and dependent on dissolution equilibrium of Cr(OH)3 and exposure of surface sites when pH > 5.
Keywords: pH; Manganese oxide minerals; Cr(III); Oxidation; Surface charge;
Self-assembly of amino-functionalized monolayers on silicon surfaces and preparation of superhydrophobic surfaces based on alkanoic acid dual layers and surface roughening by Xiaoyan Song; Jin Zhai; Yilin Wang; Lei Jiang (267-273).
Reproducibly smooth amino-functionalized surfaces were obtained by deposition of aminopropyltrimethoxysilane (APTMS) at the vapor/solid interface. Characteristics of these amino-functionalized surfaces were evaluated based on atomic force microscopy, water contact angle measurement and X-ray photoelectron spectroscopy. The results showed that APTMS modified surfaces are very homogeneous and the chemical reactivity of modified surfaces can be ensured with high free amino content. Furthermore, for the purpose of tailoring the wettability of silicon surface, dual self-assembled films were achieved by performing reaction between amino-functionalized surface and n-alkanoic acids with different chain length. The wettability of the self-assembled films can be adjusted with altering the hydrocarbon chain length of alkanoic acids. Moreover, cooperation of dual self-assembled films with surface roughening, superhydrophobic surfaces with CA larger than 153° were obtained. Thus, the wettability of modified surfaces can be altered greatly with changing hydrocarbon chain length of self-assembled films.
Keywords: Amino-functionalized surface; Dual self-assembled films; Alkanoic acids; Hydrophobicity; Chain length; Superhydrophobic surface;
Studies on electrochemical characterization and performance prediction of cellulose acetate and Zeocarb-225 composite membranes in aqueous NaCl solutions by A.K. Tiwari; Suhail Ahmad (274-281).
We have mixed cellulose acetate and Zeocarb-225 in different ratios, leading to the preparations of Membrane-1 and Membrane-2. Membrane potential, water content, and conductance measurements have been carried out to estimate and analyze the data in terms of equilibria and important electrochemical parameters. The Donnan equilibrium has been incorporated to estimate the activity coefficient of counterions, y p M , and solute, y ± M in the membrane phase along with the parameter, so called ϕ expressing non-ideality. Dependence of the extent of hydrophilicity of both membranes on mean electrolyte concentrations has been examined. Selectivity in membranes is discussed in terms of dissociation equilibria, K d s and K d f . It has been found that membrane surface charge density σ s increases with increasing of external NaCl concentration. Dependence of water transport number and cationic transport number on electrolyte concentration shows a similar trend of variation. At higher mean concentration of electrolyte, water transport number in Membrane-2 has a negative value. Membrane-2 has a higher value of water transport number than Membrane-1. The entropy production due to solute and water transport has been quantified for both the membranes in the light of nonequilibrium thermodynamics. The various type of interactions such as solute–membrane, solute–water, and water–membrane are analyzed in terms of friction coefficients ( f i j ) of Spiegler's frictional pore model. In our case, an f wm < f sm < f sw -like trend is observed in both membranes. These frictional coefficients show close dependence on external electrolyte concentrations. Pore potential values of Membrane-1 and Membrane-2 have been worked out using the Poisson–Boltzmann equation. In both systems pore potential values increase with increasing mean electrolyte concentrations. The transport through Membrane-1 and Membrane-2 tends to follow diffusion-control criteria, i.e., ( D ± ⋅ C ⋅ d / D ± M C M ⋅ δ ) ≫ 2 . A slightly higher value of solute rejection is found in Membrane-2.Co-mixing is an effective method for membrane modification. Cellulose acetate and Zeocarb-225 were mixed in different ratios giving rise Membrane-1 and Membrane-2 with distinct performances. The former had constant [ d t M + / d C mean ] value and later had distinguishable change as shown in the representative figure. In Membrane-2, the rejection was increased. (○) Membrane-1; (▵) Membrane-2.
Keywords: Co-mixed membrane; Donnan equilibrium; Dissociation equilibria; Membrane potential; Pore potential; Solute rejection;
Porous structure and fluid partitioning in polyethylene cores from 3D X-ray microtomographic imaging by M. Prodanović; W.B. Lindquist; R.S. Seright (282-297).
Using oil–wet polyethylene core models, we present the development of robust throat finding techniques for the extraction, from X-ray microtomographic images, of a pore network description of porous media having porosity up to 50%. Measurements of volume, surface area, shape factor, and principal diameters are extracted for pores and area, shape factor and principal diameters for throats. We also present results on the partitioning of wetting and non-wetting phases in the pore space at fixed volume increments of the injected fluid during a complete cycle of drainage and imbibition. We compare these results with fixed fractional flow injection, where wetting and non-wetting phase are simultaneously injected at fixed volume ratio. Finally we demonstrate the ability to differentiate three fluid phases (oil, water, air) in the pore space.We present results on the partitioning of oil and brine phases in the pore space of polyethylene cores during drainage, imbibition, and at fixed fractional flow injection. We demonstrate the ability to differentiate oil, brine and air phases in the void space.
Keywords: Porous media; Pore network models; Pore microstructure; Fluid displacement; Drainage; Imbibition;
Maximum withdrawal speed for Langmuir–Blodgett film deposition of arachidic acid by Chun-Wei Chen; Ta-Jo Liu (298-305).
The maximum withdrawal speed of Langmuir–Blodgett (LB) film deposition of arachidic acid (AA) was investigated. The quality of LB deposited film was determined by the transfer ratio (TR), together with measurements of surface roughness using atomic force microscopy (AFM). A Langmuir mini-trough was used to provide the surface pressure versus molecular area ( π – A ) curves and a flow visualization technique was applied to estimate the dynamic contact angles and to observe the fluid motion. The effects of hydrophobic and hydrophilic substrates, pH and the addition of four different ions, i.e., K+, Ba2+, Cd2+, and Al3+, on the withdrawal speed were examined. The “transition point” from liquid to solid states on the π – A curve provided a clear indication of the maximum withdrawal speed. The lower the transition point, the higher was the maximum withdrawal speed. Stable deposition was possible only if the pH of the solution was maintained in a narrow range. The observation of dynamic contact angles and fluid motion, particularly the movement of air–liquid interface, was consistent with previous findings. Owing to the “soap effect” of the divalent ions Ba2+ and Cd2+, the maximum speed for successful LB film deposition without significant water entrainment could be extended substantially with the addition of divalent ions.AFM images of LB film deposition for the AA/Ba system, the maximum coating speed V = 5 mm / min . Ten layers of molecules were coated on the substrate.
Keywords: LB film deposition; Hydrophobic and hydrophilic substrates; Arachidic acid; Divalent ions; Dynamic contact angles; Flow visualization; AFM images;
Chemical potential of a hard sphere fluid adsorbed in model disordered polydisperse matrices by Aned de Leon; O. Pizio; S. Sokołowski (306-312).
We consider a model for adsorption of a simple fluid in disordered polydisperse adsorbents. The fluid consists of hard sphere particles. On the other hand, the adsorbents of this study are modeled as a collection of hard spheres with their diameter obeying a certain distribution function. Our focus is in the evaluation of the chemical potential of the fluid immersed in such a polydisperse material. It permits us to obtain porosity and pore size distribution for the adsorbent, as well as a set of adsorption isotherms. The latter have been calculated theoretically and by grand canonical Monte Carlo simulations. We observe that the width of assumed polydispersity distribution affects all the properties of the system. Nevertheless, the effect of matrix packing is dominant in determining adsorption for this class of models. We are convinced that the matrix structures generated via more sophisticated algorithms would exhibit stronger effects of polydispersity on the entire set of properties of adsorbed simple fluids.
Keywords: Adsorption; Polydispersity; Chemical potential; Hard spheres;
Fundamental studies on the intermediate layer of a bipolar membrane by Yan-Hong Xue; Rong-Qiang Fu; Yan-xun Fu; Tong-Wen Xu (313-320).
The effect of silver ions on the water dissociation of bipolar membranes was first investigated in this paper. To do this, the bipolar membranes were prepared by immersing the anion exchange layers in an AgNO3 solution and then coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers. XPS and AES observations indicated that silver at the intermediate layer was in the form of AgCl. The experimental results proved that AgCl has an excellent catalytic function for water dissociation in terms of I – V curves, and the quantity of AgCl played an important role in the behavior of a bipolar membrane. The bipolar membranes with gelatin and the gelatin doped with silver as a catalytic layer were also prepared in the same way, and their I – V behavior and the water dissociation pilot tests were also investigated. The experimental results showed that in the case of gelatin alone, the voltage drop increased slightly at high gelatin concentrations, due mainly to the steric effect and electrostatic interaction, but decreased at low gelatin concentrations due to the hydrophilicity. However, when gelatin was doped with AgCl, the bipolar membranes have an appreciable improvement in both stability and catalytic function, in comparison with those prepared from silver or gelatin.
Keywords: Bipolar membrane; Water dissociation; Interfacial layer; Silver ion; Gelatin;
A membrane method for degassing nonaqueous liquids by M. Rzechowicz; R.M. Pashley (321-326).
Degassing of nonaqueous solvents is useful for their applications in chemical synthesis and in maintaining purity (against oxidative degradation) during long term storage. In addition, degassed solvents have been found to be of value in the production of oil and water emulsions. Currently, there are three main methods for degassing solvents. These are the freeze–pump–thaw process, partial degassing using sonication under slight vacuum and purging, where one active gas (usually oxygen) is replaced with an inert gas (e.g., nitrogen). In this work we have demonstrated the potential application of hollow-fibre membranes to efficiently degas water-immiscible, hydrophobic liquids. Mixtures of dodecane and water, separately degassed using membranes, show an enhanced dispersion of dodecane, similar to that previously reported for freeze–thaw degassed mixtures.Degassing of nonaqueous solvents is useful for their applications in chemical synthesis and in maintaining purity (against oxidative degradation) during long term storage. In addition, degassed solvents have been found to be of value in the production of oil and water emulsions. Currently, there are three main methods for degassing solvents. These are the freeze–pump–thaw process, partial degassing using sonication under slight vacuum and purging, where one active gas (usually oxygen) is replaced with an inert gas (e.g., nitrogen). In this work we have demonstrated the potential application of hollow-fibre membranes to efficiently degas water-immiscible, hydrophobic liquids. Mixtures of dodecane and water, separately degassed using membranes, show an enhanced dispersion of dodecane, similar to that previously reported for freeze–thaw degassed mixtures.
Keywords: Membranes; Degassing; Nonaqueous liquids; Laplace pressure; Ultrahydrophobic;
Temperature and concentration effects on electrolyte transport across porous thin-film composite nanofiltration membranes: Pore transport mechanisms and energetics of permeation by Ramesh R. Sharma; Shankararaman Chellam (327-340).
The influence of temperature and concentration on nanofilter charge density and electrolyte pore transport mechanisms is reported. Crossflow filtration experiments were performed to measure transport of several electrolytes (NaCl, NaNO3, NaClO4, CaCl2, MgCl2, and MgSO4) across two commercially available thin-film composite nanofiltration membranes in the range 5–41 °C. Experiments were also performed with selected salts in the range 1–50 meq/L to quantify concentration effects. Three different approaches, irreversible thermodynamics, extended Nernst–Planck formulation, and theory of rate processes, were employed to interpret retentions of these symmetric and asymmetric electrolytes at varying temperature and concentration. Increasing feed water temperature slightly increased electrolyte reflection coefficients and only weakly increased permeability compared with neutral solutes. Electromigration and convection tended to counteract each other at high fluxes explaining the weak temperature dependence of the reflection coefficient. Changes in membrane surface charge density with temperature were attributed to increased adsorption of electrolytes on the polymer constituting the active layer. Activation energy of permeation for charged solutes was primarily determined by the Donnan potential at the membrane–feed water interface. Electrolyte permeation was shown to be an enthalpy-driven process that resulted in small entropy changes. Increasing sorption capacity with temperature and low sorption energies indicated that co-ion sorption on polymeric membranes was an endothermic physicosorption process, which appears to determine temperature dependence of electrolyte permeation at increased feed concentrations.Mechanistic interpretations of changes in electrolyte selectivity of polymeric thin-film composite membranes with varying feed water temperature and concentration are provided.
Keywords: Nanofiltration; Polymeric membranes; Membrane filtration; Activation energy; Ion removal; Desalination; Membrane surface charge; Water treatment;
Chemical activation of carbon mesophase pitches by E. Mora; C. Blanco; J.A. Pajares; R. Santamaría; R. Menéndez (341-347).
This paper studies the chemical activation of mesophase pitches of different origins in order to obtain activated carbons suitable for use as electrodes in supercapacitors. The effect that the activating agent (NaOH, LiOH, and KOH), the alkaline hydroxide/pitch ratio, and the activation temperature had on the characteristics of the resultant activated carbons was studied. LiOH was found to be a noneffective activating agent, while activation with NaOH and KOH yielded activated carbons with high apparent surface areas and pore volumes. The increase of the KOH/pitch ratio caused an increase of the chemical attack on the carbon, producing higher burnoffs and development of porosity. Extremely high apparent surface areas were obtained when the petroleum pitch was activated with 5:1 KOH/carbon ratio. The increase of the activation temperature caused an increase of the burnoff, although the differences were not as significant as those derived from the use of different proportions of activating agent.N2 adsorption isotherms of carbons activated with different KOH-to-pitch ratios indicate that the increase of the proportion of KOH causes a significant increase in the development of porosity accompanied by the widening of the micropores.
Keywords: Mesophase; Activation; Surface area; Porosity; Immersion calorimetry;
Effect of temperature on the surface phase behavior of n-hexadecyl dihydrogen phosphate in adsorption layers at the air–water interface by Md. Mufazzal Hossain; Ken-ichi Iimura; Teiji Kato (348-355).
We present the adsorption kinetics and the surface phase behavior of n-hexadecyl dihydrogen phosphate (n-HDP) at the air–water interface by film balance and Brewster angle microscopy (BAM). A phase diagram, which shows a triple point at about 25.8 °C, is constructed by measuring the surface pressure (π)–time (t) adsorption isotherms. Below 25.8 °C, each of the π – t curves shows a plateau at about zero surface pressure indicating the existence of a first-order phase transition. The BAM observation confirms the order of this phase transition by presenting two-surface phases during this plateau. However, the BAM observation also shows clearly another second-order phase transition from an isotropic phase to a mosaic-textured liquid condensed (LC) phase. The initial phase is a gas (G) phase. Considering the peculiarity of the middle phase, we suggest this phase as an intermediate (I) phase. Above the triple point, the π – t curves predict the existence of two-step first-order phase transitions. Similar to the results at lower temperatures, the BAM images show two-surface phases during these first-order phase transitions together with a second-order phase transition from an isotropic phase to an LC phase. These transitions are classified as a first-order G–LE (liquid expanded) phase transition, which is followed by another first-order LE–I phase transition. The second-order phase transition is an I–LC phase transition. Contrary to these results, at 36 °C both the π – t measurements and the BAM observation present only two first-order phase transitions, which are G–LE at zero surface pressure and LE–LC transition at higher surface pressure. The shape of the domains during the main transitions shows a peculiar change from a circular at 20 °C to an elongated at 24 °C and finally to a circular shape at 36 °C. Such a change in the domain shapes has been explained considering the dehydration effect at higher temperatures as well as the nature of phases.
Keywords: Gibbs monolayers; Phase transition; Phase diagram; Surface pressure; Brewster angle microscopy; n-Hexadecyl dihydrogen phosphate;
Flux-assisted wetting and spreading of Al on TiC by V.H. López; A.R. Kennedy (356-362).
The effect of a K–Al–F-based flux on the spreading of Al on TiC, at temperatures up to 900 °C, in Ar and in air has been studied. Whilst obtuse contact angles were observed without flux, the flux facilitated rapid spreading to a perfect wetting condition, in both Ar and in air. The atmosphere was found to have a weak effect on the spreading kinetics as the liquid flux provides a locally protective atmosphere by spreading over the TiC surface and also on the solid surface of Al. The flux dissolves the aluminium oxide, covering Al, so that when Al melts, and the oxide layer has been removed or weakened, intimate contact occurs between liquid Al and the TiC substrate facilitating spontaneous spreading and instantaneous wetting of liquid Al on TiC. Since flux-assisted spreading is very rapid and occurs without the formation of a reaction layer at the Al/TiC interface, this process is very different to the reactive wetting behaviour previously reported in the Al–TiC system.The figure above shows the effect of a K–Al–F-based flux on the spreading of Al on TiC. The rapid spreading times and absence of thick reaction layers at the Al/TiC interface are very different to the reactive wetting behaviour previously reported in the Al–TiC system.
Keywords: Wetting; TiC; Flux; Spreading;
The effect of octyl glucoside on rheological behavior of diluted and concentrated lamellar phases by N. Granizo; M. Álvarez; M. Valiente (363-368).
We have investigated the rheological properties of lamellar liquid crystal formed by nonionic surfactants at low and high surfactant concentrations with a small amount of octyl glucoside and their relationship with the topology of the bilayer. Rheology is a specific signature of each bilayer topology. The decrease in viscosity by increasing the shear rate according to a power law with exponent close to −0.8 was found for the concentrated system of LSB/1-butanol/water and 1% in weight of OG. On the contrary, the decrease in the viscosity by increasing the shear rate for the diluted system is less pronounced with lower exponent values. The rheological data agrees with the presence of vesicles. A special case is the system with benzyl alcohol. The apparent viscosity does not follow the same power law than for alkanols.
Keywords: Vesicle; Lamellar liquid crystal; Surfactant; Rheology; Shear rate; Octyl glucoside; Viscosity;
Numerical investigation of the effect of insoluble surfactants on drop deformation and breakup in simple shear flow by Ivan B. Bazhlekov; Patrick D. Anderson; Han E.H. Meijer (369-394).
The effect of insoluble surfactants on drop deformation and breakup in simple shear flow is studied using a combination of a three-dimensional boundary-integral method and a finite-volume method to solve the coupled fluid dynamics and surfactant transport problem over the evolving interface. The interfacial tension depends nonlinearly on the surfactant concentration, and is described by the equation of state for the Langmuir isotherm. Results are presented over the entire range of the viscosity's ratio λ and the surface coverage x, as well as the capillary number Ca that spans from that for small deformation to values that are beyond the critical one Ca cr . The values of the elasticity number E, which reflects the sensitivity of the interfacial tension to the maximum surfactant concentration, are chosen in the interval 0.1 ⩽ E ⩽ 0.4 and a convection dominated regime of surfactant transport, where the influence of the surfactant on drop deformation is the most significant, is considered. For a better understanding of the processes involved, the effect of surfactants on the drop dynamics is decoupled into three surfactant related mechanisms (dilution, Marangoni stress and stretching) and their influence is separately investigated. The dependence of the critical capillary number Ca cr ( λ ) on the surface coverage is obtained and the boundaries between different modes of breakup (tip-streaming and drop fragmentation) in the (λ; x) plane are searched for. The numerical results indicate that at low capillary number, even with a trace amount of surfactant, the interface is immobilized, which has also been observed by previous studies. In addition, it is shown that for large Péclet numbers the use of the small deformation theory to measure the interfacial tension in the case where surfactants are present can introduce a significant error.The effect of insoluble surfactants on drop deformation and breakup in simple shear flow is studied. The dependence of the critical capillary number Ca cr ( λ ) on the surface coverage is obtained and the boundaries between different modes of breakup in the (λ; x) plane are searched for.
Keywords: Drop deformation; Drop breakup; Surfactant; Interfacial tension; Marangoni stress; Tip steaming; Shear flow; Boundary integral method;
Mixed micellization and interfacial properties of dodecyltrimethylammonium bromide and tetraethyleneglycol mono-n-dodecyl ether in absence and presence of sodium propionate by Aijaz A. Dar; Bedachanda Chatterjee; Ghulam M. Rather; Akhil R. Das (395-405).
Mixed micelle formation and interfacial properties of aqueous binary surfactant combinations of dodecyltrimethylammonium bromide (C12TAB) and tetraethyleneglycol mono-n-dodecyl ether (C12E4) at 30 °C in absence and presence of sodium propionate (NaPr) have been investigated. The critical micelle concentration, aggregation number, micropolarity and interfacial adsorption have been quantitatively estimated by surface tension and steady-state fluorescence measurements. The micellar and adsorption characteristics like composition, activity coefficients and mutual interaction parameters have been estimated following different theoretical treatments like that of Clint, Rubingh, Rodenas, Maeda, Blankschtein and Rosen. The analysis reveals very small mole fraction of cationic surfactant in both the mixed micelles and mixed monolayer inspite of synergism. Blankschtein's model predicts a continuous decrease in synergism due to the salt effect of NaPr; Rubingh's approach, on the contrary, indicates an increase in it above 30 mM of NaPr concentration. Aggregation number variation with NaPr indicates the same. Mixed monolayer shows better synergism compared to that in mixed micelles which increases with the addition of sodium propionate above 30 mM concentration.Mixed micelle formation and interfacial properties of aqueous binary surfactant combinations of dodecyltrimethylammonium bromide (C12TAB) and tetraethyleneglycol mono-n-dodecyl ether (C12E4) at 30 °C show synergism which gets enhanced on addition of sodium propionate above 30 mM concentration.
Keywords: Mixed micelle formation; Synergism; Mixed monolayer formation; Interaction parameter; Hydrophobic counterions; Micropolarity; Aggregation number; Counterion binding;
High internal phase CO2-in-water emulsions stabilized with a branched nonionic hydrocarbon surfactant by Varun V. Dhanuka; Jasper L. Dickson; Won Ryoo; Keith P. Johnston (406-418).
A nonionic-methylated branched hydrocarbon surfactant, octa(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether (5b-C12E8) emulsifies up to 90% CO2 in water with polyhedral cells smaller than 10 μm, as characterized by optical microscopy. The stability of these concentrated CO2/water (C/W) emulsions increases with pressure and in some cases exceeds 24 h. An increase in pressure weakens the attractive van der Waals interactions between the CO2 cells across water and raises the disjoining pressure. It also enhances the solution of the surfactant tail and drives the surfactant from water towards the water–CO2 interface, as characterized by the change in emulsion phase behavior and the decrease in interfacial tension (γ) to 2.1 mN/m. As the surfactant adsorption increases, the greater tendency for ion adsorption is likely to increase the electrostatic repulsion in the thin lamellae and raise the disjoining pressure. As pressure increases, the increase in disjoining pressure and decrease in the capillary pressure (due to the decrease in γ) each favor greater stability of the lamellae against rupture. The electrical conductivity is predicted successfully as a function of Bruggeman's model for concentrated emulsions. Significant differences in the stability are observed for concentrated C/W emulsions at elevated pressure versus air/W or C/W foams at atmospheric pressure.Carbon dioxide/water concentrated emulsion at 345 bar with cells on the order 10 μm stabilized with a nonionic hydrocarbon surfactant.
Keywords: Concentrated emulsion; Carbon dioxide; Interfacial tension; High pressure;
Cloud point extraction and simultaneous determination of zirconium and hafnium using ICP-OES by Shahab Shariati; Yadollah Yamini (419-425).
In the present study a simple versatile separation method using cloud point procedure for extraction of trace levels of zirconium and hafnium is proposed. The extraction of analytes from aqueous samples was performed in the presence of quinalizarine as chelating agent and Triton X-114 as a non-ionic surfactant. After phase separation, the surfactant-rich phase was diluted with 30% (v/v) propanol solution containing 1 mol l−1 HNO3. Then, the enriched analytes in the surfactant-rich phase were determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The different variables affecting the complexation and extraction conditions were optimized. Under the optimum conditions (i.e. 3.4 × 10 −5 mol l −1 quinalizarine, 0.1% (w/v) Triton X-114, 55 °C equilibrium temperature) the calibration graphs were linear in the range of 0.5–1000 μg l−1 with detection limits (DLs) of 0.26 and 0.31 μg l−1 for Zr and Hf, respectively. Under the presence of foreign ions no significant interference was observed. The precision (%RSD) for 8 replicate determinations at 200 μg l−1 of Zr and Hf was better than 2.9% and the enrichment factors were obtained as 38.9 and 35.8 for Zr and Hf, respectively. Finally, the proposed method was successfully utilized for the determination of these cations in water and alloy samples.
Keywords: Cloud point extraction; Zirconium; Hafnium; Quinalizarine; Triton X-114;
Temperature effects upon aqueous micellar-assisted decarboxylation of 6-nitrobenzisoxazole-3-carboxylate and its 5-methyl derivative by Lucia Brinchi; Raimondo Germani; Laura Goracci; Gianfranco Savelli; Nicoletta Spreti; Pietro Di Profio (426-431).
An investigation of temperature effects upon first-order rate constants in the micellar pseudophase for decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) and its 5-methyl derivative (6-NBIC-5-Me) was carried out. Surfactants used were cationic cetyltrialkylammonium bromide with alkyl = methyl (CTABr), ethyl (CTEABr), n-propyl (CTPABr), and n-butyl (CTBABr). The investigation shows that micelles speed up reactions by decreasing enthalpies of activation. Increase in head group bulk further speeds reactions still by a small decrease in the enthalpies, for both substrates. Values of Δ H # and Δ S # for 6-NBIC in the various surfactants give linear isokinetic plot, with CTBABr as outlier.
Keywords: 6-Nitrobenzisoxazole-3-carboxylate; Micelle-activation parameters; Monomolecular reaction;
The temperature dependence of the heat capacity change for micellization of nonionic surfactants by Gordon C. Kresheck (432-440).
The thermodynamic parameters that govern micelle formation by four different nonionic surfactants were investigated by ITC and DSC. These included n-dodecyldimethylphosphine oxide (APO12), Triton X-100 (TX-100), n-octyltetraoxyethylene (C8E4), and N , N -dimethyloctylamine-N-oxide (DAO8). All of these surfactants had been previously investigated by solution calorimetry over smaller temperature ranges with conflicting conclusions as to the temperature dependence of the heat capacity change, ΔCp, for the process. The temperature coefficient of the heat capacity change, B (cal/mol K2), was derived from the enthalpy data that were obtained at small intervals over a broad temperature range. The values obtained for each of the surfactants at 298.2 K for ΔCp and B were − 155 ± 2 and 0.50 ± 0.36 (APO12), − 97 ± 3 and − 0.24 ± 0.18 (TX-100), − 105 ± 2 and 1.0 ± 0.3 (C8E4), and − 82 ± 1 and 0.36 ± 0.04 (DAO8), cal/mol K and cal/mol K2, respectively. The resulting B-values did not correlate with the cmc, aggregation number, or structure of the monomer in an obvious way, but they were found to reflect the relative changes in hydration of the polar and nonpolar portions of the surfactant molecule as the micelles are formed. An analysis of the data obtained from DSC scans was used to describe the temperature dependence of the critical micelle concentration, cmc. An abrupt increase in heat capacity was observed for TX-100 and C8E4 solutions of 36.5 ± 0.5 and 21 ± 5 cal / mol K , respectively, as the temperature of the scan passed through the cloud point. This change in heat capacity may reflect the increased monomer concentration of the solutions that accompanies phase separation, although other interpretations of this jump are possible.A nonlinear plot of the enthalpy change for micelle formation leads to a temperature dependent heat capacity change for the process. DSC may be used as an independent method to determine the temperature dependence of the cmc and describe the enthalpy and heat capacity changes that accompany liquid/liquid phase separation at the cloud point.
Keywords: Titration calorimetry; Differential scanning calorimetry; Micelles; Cloud point; Critical micelle concentration;
Calculation of hydrophile–lipophile balance for polyethoxylated surfactants by group contribution method by Xiaowen Guo; Zongming Rong; Xugen Ying (441-450).
Based on Davies' group contribution method, hydrophile–lipophile balance (HLB) values were calculated by effective chain length (ECL) instead of actual chain length of straight alkyl chain, polyoxyethylene (EO) chain, and polyoxypropylene (PO) chain. Linear equations were adopted for the effective chain length of straight alkyl chain and PO chain; a Gamma probability density function (PDF) was used to describe the contribution of each EO group to HLB and the effective chain length of EO chain could be obtained by integrating Gamma PDF. The HLB values of 224 nonionic surfactants were calculated and the average absolute error is less than 1.5, which is much better than the results obtained by Davies.Effective chain length equations were introduced to calculate the HLB values of polyethoxylated surfactants. The integral of the Gamma probability density function was used to describe the contribution of the polyoxyethylene chain to HLB.
Keywords: HLB; Group contribution method; Polyethoxylated surfactants; Effective chain length; Gamma PDF;
Characterization of micelle formation of dodecyldimethyl-N-2-phenoxyethylammonium bromide in aqueous solution by Dibyendu Khatua; Abhisek Gupta; Joykrishna Dey (451-456).
Aggregation behavior of dodecyldimethyl-N-2-phenoxyethylammonium bromide commonly called domiphen bromide (DB) was studied in aqueous solution. The Krafft temperature of the surfactant was measured. The surfactant has been shown to form micellar structures in a wide concentration range. The critical micelle concentration was determined by surface tension, conductivity, and fluorescence methods. The conductivity data were also employed to determine the degree of surfactant counterion dissociation. The changes in Gibb's free energy, enthalpy, and entropy of the micellization process were determined at different temperature. The steady-state fluorescence quenching measurements with pyrene and N-phenyl-1-naphthylamine as fluorescence probes were performed to obtain micellar aggregation number. The results were compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant. The micelle formation is energetically more favored in DB compared to that in DTAB. The 1H-NMR spectra were used to show that the 2-phenoxyethyl group, which folds back onto the micellar surface facilitates aggregate formation in DB.Aggregation behavior of domiphen bromide (DB) was studied in aqueous solution. The critical micelle concentration (CMC) was determined by surface tension, conductivity, and fluorescence methods. The changes in Gibb's free energy, enthalpy, and entropy of the micellization process have been determined at different temperature. The steady-state fluorescence quenching measurements with pyrene as fluorescence probe was employed to obtain micellar aggregation number. The micropolarity and microviscosity of the micelles were estimated by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene probes, respectively. The results have been compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant.
Keywords: Domiphen bromide; Krafft temperature; CMC; Gibbs free energy; Enthalpy; Entropy;
Sodium dodecyl sulfate promoting a cooperative association process of sodium cholate with bovine serum albumin by Bianca Schweitzer; Arlindo C. Felippe; Alexandre Dal Bó; Edson Minatti; Dino Zanette; Antonio Lopes (457-466).
Sodium cholate (NaC) was used as a representative bile salt in the process of cooperative binding to bovine serum albumin (BSA) in a mixture with sodium dodecyl sulfate (SDS). The experiments were performed in 0.02 M Tris–HCl buffer solution (pH 7.50), in the presence of 0.1% BSA and at 25 °C. The aim of this study is to provide information on the performance of the BSA in the promotion of cooperative binding of sodium cholate promoted by the presence of SDS. The method used to monitor the binding was based on the analysis of the effect of SDS and NaC concentrations and their mixtures upon the fluorescence intensity of the BSA tryptophan residues. Plots of the fluorescence emission bands in terms of the A 0 / A ratio vs surfactant concentrations, where A 0 and A represent the areas of emission bands in the presence and absence of the surfactants, respectively, were drawn in order to investigate the surfactant interaction with the protein. An alternative methodology, the specific conductivity vs surfactant concentration plots, was used, which involves mixtures of SDS and NaC to investigate the association processes, through the determination of the critical aggregation concentration (cac, when in the presence of protein) and the critical micellar concentration (cmc). The results led to a general conclusion that as the mixed micellar aggregates become richer in the bile salt monomer, the tendency to lose the reactivity with the protein increases. According to our results, a clear evidence of the predomination of BSA–SDS–NaC complexes is found only for the SDS molar fraction above ≈0.6, and below this fraction a tendency toward free mixed micelles starts to predominate.
Keywords: Bovine serum albumin; BSA; Sodium cholate; Protein–surfactant interaction; Anionic surfactant mixtures; Fluorescence quenching; Sodium dodecyl sulfate;
Model analysis of the colloid and radionuclide retardation experiment at the Grimsel Test Site by Susumu Kurosawa; Scott C. James; Mikazu Yui; Motomu Ibaraki (467-475).
The colloid and radionuclide retardation experiments performed at NAGRA's Grimsel Test Site in Switzerland are part of an international collaboration program designed to collect in situ data on the impacts of colloids on radionuclide transport. In this work, breakthrough behaviors of trivalent americium (i.e., 241Am and 243Am) both in the absence and presence of bentonite colloids are analyzed with COLFRAC—a code that models colloid-facilitated solute transport in discretely-fractured, porous media. Model fits to the experimental results indicate that Am sorbed onto mobile colloids, which enhance Am transport relative to a non-sorbing tracer, 131I. Modelling results suggest that Am is kinetically sorbed onto both naturally occurring and exogenous bentonite colloids. Results also indicate that desorption of Am from colloids is slow with respect to the duration of the experiment. In addition, early colloid breakthrough compared to a conservative tracer suggests the effects of hydrodynamic chromatography. Overall, Am breakthrough curves suggest enhanced mobility due to co-transport with both naturally occurring and bentonite colloids.Radionuclide breakthrough results in in situ radionuclides and colloids co-transport experiments are best explained by a model (COLFRAC code) using a kinetic process for sorption of radionuclides onto colloids. (a) 243Am: no sorption onto colloids, (b) 243Am: equilibrium sorption onto natural colloids, (c) 243Am: kinetic sorption onto natural colloids, (d) 243Am: kinetic sorption onto natural colloids including HDC.
Keywords: Radionuclide and colloid transport; In situ experiment; Fractured media; Model analysis; Kinetic sorption reaction;
Diffusioosmosis of electrolyte solutions in a fine capillary slit by Hsien Chen Ma; Huan J. Keh (476-486).
The steady diffusioosmotic flows of an electrolyte solution along a charged plane wall and in a capillary channel between two identical parallel charged plates generated by an imposed tangential concentration gradient are theoretically investigated. The plane walls may have either a constant surface potential or a constant surface charge density. The electrical double layers adjacent to the charged walls may have an arbitrary thickness and their electrostatic potential distributions are determined by the Poisson–Boltzmann equation. Solving a modified Navier–Stokes equation with the constraint of no net electric current arising from the cocurrent diffusion, electric migration, and diffusioosmotic convection of the electrolyte ions, the macroscopic electric field and the fluid velocity along the tangential direction induced by the imposed electrolyte concentration gradient are obtained semianalytically as a function of the lateral position in a self-consistent way. The direction of the diffusioosmotic flow relative to the concentration gradient is determined by the combination of the zeta potential (or surface charge density) of the wall, the properties of the electrolyte solution, and other relevant factors. For a given concentration gradient of an electrolyte along a plane wall, the magnitude of fluid velocity at a position in general increases with an increase in its electrokinetic distance from the wall, but there are exceptions. The effect of the lateral distribution of the induced tangential electric field and the relaxation effect in the double layer on the diffusioosmotic flow are found to be very significant.The diffusioosmosis of an electrolyte solution in a capillary slit generated by an imposed tangential concentration gradient is theoretically studied in a self-consistent way.
Keywords: Diffusioosmosis; Plane wall; Capillary slit; Diffusiophoresis;
A novel method to prepare inorganic water-soluble nanocrystals by Barbara Salvadori; GianCarlo Capitani; Marcello Mellini; Luigi Dei (487-490).
Calcium sulphate dihydrate nanocrystals of 25–100 nm width have been synthesized in 100% purity and yield by means of a method—the cryo-vacuum process—consisting of rapid freezing of quasi-saturated solutions and subsequent vacuum assisted sublimation of water. Transmission electron microscopy reveals both curled nano-lamellae and smaller, irregular particles; electron diffraction patterns demonstrated that the particles are crystalline. This is a very powerful method for the ‘clean’ synthesis of moderately and completely water-soluble inorganic materials.
Keywords: Nanocrystals synthesis; Calcium sulphate dihydrate; Cryo-vacuum process;
Effect of interfacial mobility on rupture of thin stagnant films on a solid surface due to random mechanical perturbations by Ganesan Narsimhan; Zebin Wang (491-496).
Previous analysis of Narsimhan [G. Narsimhan, J. Colloid Interface Sci. 287 (2005) 624–633] for the evaluation of rupture of a nondraining thin film on a solid support due to imposed random mechanical perturbations modeled as a Gaussian white noise has been extended for partially mobile gas–liquid interfaces. The average rupture time of film is evaluated by first passage time analysis (as the mean time for the amplitude of perturbation to become equal to film thickness). The interfacial mobility is accounted for through surface viscosity as well as Marangoni effect. The mean rupture time for partially mobile gas–liquid interface, as characterized by two dimensionless groups, dimensionless surface viscosity and Marangoni number, lies between the two extreme limits for fully mobile and immobile films. The critical wavenumber for minimum rupture time is shown to be insensitive to interfacial mobility. However, the critical dimensionless surface viscosity and critical Marangoni number at which the behavior of thin film deviates from that of fully mobile film and the behavior approaches that of fully immobile film are smaller for higher Hamaker constants, smaller film thickness and smaller surface potentials.The average lifetime of a thin film with mobile interface on a solid surface subjected to random Gaussian pressure fluctuations has been evaluated by a first passage time analysis.
Keywords: Thin film rupture; Interfacial mobility; Surface viscosity; Marangoni effect; Thermal fluctuations; Pressure fluctuations; First passage time; Van der Waals forces; Electrostatic forces; Disjoining pressure; Stagnant thin film;
Maximum stability of a single spherical particle attached to an emulsion drop by Michael J. Hey; John G. Kingston (497-499).
The stability of a single, solid, spherical particle attached to a liquid drop in an emulsion is discussed. Ignoring effects due to gravity and line tension, we calculate the energies required to either detach the particle from the drop or to engulf the particle within the drop. The stability of the attached particle is here defined as the smaller of these two energies. A simple formula is derived for the value of Young's angle which gives maximum stability for a given radius ratio of particle to detached drop. For maximum stability the particle should be preferentially wetted by the liquid forming the drop.
Keywords: Contact angle; Young's equation; Solid-stabilised emulsions;
by Arthur Hubbard (500).