Journal of Colloid And Interface Science (v.338, #1)
Cover 1/Editorial Board (OFC).
Deposition kinetics of bacteriophage MS2 to natural organic matter: Role of divalent cations by Mai Pham; Eric A. Mintz; Thanh H. Nguyen (1-9).
Experimental results demonstrated that attachment efficiencies of MS2 onto the SRNOM surface were seven to seventeen times higher in the presence of Ca2+ than in the presence of Mg2+.The role of divalent cations (i.e. Ca2+ and Mg2+) in the deposition kinetics of the bacteriophage MS2 onto flat bare silica surfaces and Suwannee River Natural Organic Matter (SRNOM)-coated silica surfaces was investigated using a Quartz Crystal Microbalance (QCM) coupled with a radial stagnation point flow (RSPF) system. Experimental results demonstrated that attachment efficiencies of MS2 onto the SRNOM surface were seven to seventeen times higher in the presence of Ca2+ than in the presence of Mg2+. A similar trend was observed for the adsorption of polyglutamic acid, which is one of the carboxylate-containing amino acid residues found on the surface of MS2 capsids present on SRNOM-coated surfaces. The difference in attachment rates in a solution containing either Ca2+ or Mg2+ can be explained by a stronger tendency of Ca2+ compared to Mg2+ to form cation bridges by binding to carboxylate groups of both the SRNOM and the MS2 capsids. Moreover, higher attachment efficiencies of MS2 onto the SRNOM-coated silica surfaces compared to those on bare silica surfaces in the presence of either Ca2+ or Mg2+ at concentrations higher than 0.3 mM emphasized the important role of SRNOM carboxylate groups. Experimental data also showed reduced attachment efficiency of MS2 to SRNOM-coated surfaces in solution containing 1 mg/L SRNOM.
Keywords: Deposition; Adsorption; Bacteriophage; Natural organic matter; Divalent cations; Quartz crystal microbalance;
Acid–base properties of the alumina surface: Influence of the titration procedures on the microcalorimetric results by Jean-Pierre Morel; Nicolas Marmier; Charlotte Hurel; Nicole Morel-Desrosiers (10-15).
Thermogram obtained by Microcalorimetry using HCl 0.100 Mol L−1.The enthalpy changes associated with the protonation and deprotonation of an alumina surface have been determined on the basis of microcalorimetry experiments and acid–base potentiometric titrations at 25 °C. It has been shown that the results may vary significantly according to the experimental procedure. In order to do so, the potentiometric and microcalorimetric titrations have been carried out first from an acidic pH to basic pH and second from a pH near the pHzpc of alumina to acidic or basic pH. It has been demonstrated that the pK a values deduced from the potentiometric titrations are the same whatever the experimental protocol whereas the only way to obtain meaningful enthalpies of proton exchange is to carry out microcalorimetric titrations by starting around the point of zero charge.
Keywords: Alumina; Microcalorimetry; Sorption; Temperature effect;
Probing the interaction of the amino acid alanine with the surface of ZnO ( 1 0 1 ¯ 0 ) by Y.K. Gao; F. Traeger; O. Shekhah; H. Idriss; C. Wöll (16-21).
Alanine molecule on ZnO ( 1 0 1 ¯ 0 ) surface. Energy minimized structure of the most stable configuration: dissociatively adsorbed bidentate alanine on the surface. Structure is optimized using Car Parinello Molecular Dynamics (CPMD) as implemented by density functional theory.The adsorption modes and stability of the amino acid alanine (NH2–CH(CH3)–COOH) have been studied on the nonpolar single crystal surface of zinc oxide, ZnO ( 1 0 1 ¯ 0 ) , experimentally by X-ray photoelectron spectroscopy (XPS) and computationally using density functional theory (DFT). Deposition at 200 K was found to lead to the formation of multilayers identified by an XPS N1s peak at 401.7 eV assigned to the NH 3 + group, a fingerprint of the zwitterionic structure of alanine in the solid state. Heating to 300 K resulted in the removal of most of the multilayers with the remaining surface coverage estimated to 0.4 with respect to Zn cations. At this temperature most of the alanine molecules are found to be deprotonated (dissociated), yielding a carboxylate species (NH2–CH(CH3)–COO− (a) + OH (s); where O is surface oxygen, (a) for adsorbed and (s) for surface species). Further heating of the surface resulted in a gradual decrease of the surface coverage and by 500 K a large fraction of adsorbed alanine molecules have desorbed from the surface. Total energy DFT computations of different adsorbate species identified two stable dissociative adsorption modes: bidentate and monodentate. The bidentate species with adsorption energy of 1.75 eV was found to be more stable than the monodentate species by about 0.7 eV.
Keywords: Alanine; ZnO; Single crystal; Adsorption; XPS; DFT; Monodendate; Bidentate; Zwitterion;
Preparation and characterization of zirconium-based magnetic sorbent for arsenate removal by Yu-Ming Zheng; Soh-Fong Lim; J. Paul Chen (22-29).
Graphical Abstract of “Preparation and characterization of zirconium-based magnetic sorbent for arsenate removal” (by Yu-Ming Zheng, Soh-Fong Lim, J. Paul Chen).In this study, a zirconium-based magnetic sorbent is developed by a coprecipitation technology. The characterization of the sorbent and its adsorption behavior are systematically investigated. It is shown that the sorbent has a small mean diameter of 543.7 nm, a specific surface area of 151 m2/g, and a pHzpc of 7. The sorbent has a rough surface and many pores developed on the surface. It has a molecular formula of ZrO(OH)2·1.6Fe3O4·2.5H2O, which was determined by the thermal gravimetric analysis, the elemental analysis, and the digestion experiments. The sorption equilibrium can be reached within 25 h. Better adsorption can be obtained at lower pH, and the optimal initial pH is from 2.6 to 3.3. The maximum adsorption capacity of 45.6 mg-As/g is achieved, which is much higher than many reported sorbents. FTIR spectra analysis indicates that –OH groups play an important role in the uptake. Some of the arsenate are reduced to arsenite after its adsorption onto the magnetic sorbent; the divalent iron in the sorbent may provide electrons for the reduction. A conceptual model for the adsorption of arsenate by the magnetic sorbent is proposed to illustrate the mechanism.
Keywords: Adsorption; Arsenate; Iron; Magnetic sorbent; Spectroscopic analysis; Zirconium;
RETRACTED: Immobilization of 5-amino-1,3,4-thiadiazole-thiol onto kanemite for thorium(IV) removal: Thermodynamics and equilibrium study by Denis L. Guerra; Marcos A. Carvalho; Victor L. Leidens; Alane A. Pinto; Rúbia R. Viana; Claudio Airoldi (30-39).
This article has been retracted at the request of the Editors of Journal of Colloid and Interface Science as fraudulent results have been found in this article and other publications in Elsevier journals by the same authors, namely: J. Colloid Interface Sci., 337 (2009) 122–130; Inorg. Chem. Commun., 12 (2009) 1145–1149; J. Environ. Radioact., 101 (2010) 122–133; Process Safety Environ., 88 (2010) 53–61; J. Phys. Chem. Solids, 70 (2009) 1413–1421; Appl. Surf. Sci., 256 (2009) 702–709; Inorg. Chem. Commun., 11 (2008) 20–23; Inorg. Chem. Commun., 12 (2009) 1107–1111; J. Hazardous Mater., 172 (2009) 507–514; J. Hazardous Mater., 171 (2009) 514–523; J. Colloid Interface Sci., 338 (2009) 30–39.Publication of an article in a peer-reviewed journal is an important building-block in the development of science. Elsevier has defined policies and ethical guidelines that have to be obeyed by authors and editors and Elsevier takes its duties of guardianship over the scholarly record extremely seriously.The Editors of the Elsevier journals involved found that the allegations of fraud are conclusive and they have decided that these papers should be retracted from the journals.
Thermoresponsive surfaces prepared using adsorption of a cationic graft copolymer: A versatile method for triggered particle capture by R. Liu; B.R. Saunders (40-47).
We study a new, versatile method for preparing thermoresponsive surfaces using adsorption of a preformed cationic graft poly(N-isopropylacrylamide) copolymer which enables substrates to show temperature-triggered particle capture.In this study we investigate triggered particle capture at substrates containing adsorbed thermally responsive graft copolymers. The copolymers used were PDMA x + - g - ( PNIPAm n ) y , where DMA + is quaternized N,N-dimethylaminoethyl methacrylate and NIPAm is N-isopropylacrylamide. The x and y values originate from the macroinitiator used for copolymer preparation. In this study the copolymers are adsorbed onto two different substrates: quartz microscope slides and microporous, high surface area carbon foam. The substrates were coated with a layer of calcined LAPONITE®. The LAPONITE® acted as a conditioning layer and promoted strong adsorption of the copolymer. The hydrophobicity of the thermoresponsive surfaces was probed using variable-temperature contact angle measurements. The contact angles generally increased considerably upon increasing the temperature to above the lower critical solution temperature (LCST) of the copolymers. The ability of the thermoresponsive surfaces to capture dispersed particles was investigated using anionic and cationic polystyrene (PS) particles. PDMA 30 + - g - ( PNIPAm 210 ) 14 was the most effective copolymer in terms of providing high capture efficiencies of anionic PS particles using temperature as the trigger. The thermoresponsive surfaces strongly held the anionic PS particles even when cooled to below the LCST. The relationships between copolymer structure and particle capture efficiency are discussed. The new approach used here for preparation thermoresponsive surfaces is potentially scalable to high volume applications.
Keywords: Isopropylacrylamide; Thermoresponsive; Particle capture; Graft copolymer;
Selenium adsorption to aluminum-based water treatment residuals by James A. Ippolito; Kirk G. Scheckel; Ken A. Barbarick (48-55).
Water treatment residuals normalized absorption of (A) selenite K-edge XAS spectra as a function of anoxic Se(IV), anoxic or oxic Se(IV) adsorption followed by 4 weeks of air purging and (B) Fourier-transformed actual (solid line) versus fitted (dotted line) data.Aluminum-based water treatment residuals (WTR) can adsorb water- and soil-borne P, As(V), As(III), and perchlorate, and may be able to adsorb excess environmental selenium. WTR, clay minerals, and amorphous aluminum hydroxide were shaken for 24 h in selenate or selenite solutions at pH values of 5–9, and then analyzed for selenium content. Selenate and selenite adsorption edges were unaffected across the pH range studied. Selenate adsorbed on to WTR, reference mineral phases, and amorphous aluminum hydroxide occurred as outer sphere complexes (relatively loosely bound), while selenite adsorption was identified as inner-sphere complexation (relatively tightly bound). Selenite sorption to WTR in an anoxic environment reduced Se(IV) to Se(0), and oxidation of Se(0) or Se(IV) appeared irreversible once sorbed to WTR. Al-based WTR could play a favorable role in sequestering excess Se in affected water sources.
Keywords: Inner-sphere complexation; Outer-sphere complexation; Selenate; Selenite; X-ray absorption spectroscopy;
Preparation and characterization of nanoparticles based on dextran–drug conjugates by Stephanie Hornig; Heike Bunjes; Thomas Heinze (56-62).
Dextran–drug (ibuprofen, naproxen) conjugates were prepared, characterized and formulated into nanoparticles with high loading efficiency applying nanoprecipitation.The presented concept combines the widely-established use of macromolecular prodrugs with nanoparticulate drug delivery devices. For this purpose, the water-soluble biopolymer dextran was functionalized with poorly water-soluble drugs (ibuprofen, naproxen) via in situ activation of the carboxylic groups with N, N ′-carbonyldiimidazole (CDI). The resulting hydrophobic derivatives self-assemble into nanoparticles with high loading efficiency during nanoprecipitation. The degree of substitution (DS) and the preparation technique strongly influence the size and the size distribution of the resulting nanoparticles. The particle suspensions remained stable over months in a pH value range between 4 and 11. Derivatives with high DS values are more stable against hydrolysis and after the addition of electrolytes than lowly substituted ones. Therefore, a defined tuning of the DS value may allow the adjustment of the pH-dependent hydrolysis rate and, hence, the release of the drugs.
Keywords: Dextran; Drug delivery; Polymer–drug conjugates; Nanoparticle; Ibuprofen;
Prediction models for shape and size of ca-alginate macrobeads produced through extrusion–dripping method by Eng-Seng Chan; Boon-Beng Lee; Pogaku Ravindra; Denis Poncelet (63-72).
The shape diagram reveals a clear operating region and the process limits within which spherical ca-alginate beads could be formed.The aim of this work was to develop prediction models for shape and size of ca-alginate macrobeads produced through extrusion–dripping method. The relationship between the process variables on the shape and size of the alginate drops before and after gelation was established with the aid of image analysis. The results show that a critical Ohnersorge number (Oh) > 0.24 was required to form spherical beads. The shape transition of ca-alginate beads could be typically distinguished into three phases along the collecting distance and it was affected by the combined influence of the solution properties, the collecting distance and the drop size. Mathematical equations and a master shape diagram were developed to reveal a clear operating region and the overall process limits within which spherical ca-alginate beads could be formed. In terms of bead size, the overall size correction factor (K) which accounted for the liquid loss factor (k LF ) and the shrinkage factor (k SF ), varied between 0.73 and 0.85 under the experimental conditions. The size prediction model correlated well with the experimental data. The approach and the outcome could be used as a model to develop prediction tools for similar bead production systems.
Keywords: Shape; Size; Extrusion; Bead; Drop; Encapsulation; Alginate;
Evaluation of adhesion force between functionalized microbeads and protein-coated stainless steel using shear-flow-induced detachment by Muriel Mercier-Bonin; Mathieu Adoue; Sandrine Zanna; Philippe Marcus; Didier Combes; Philippe Schmitz (73-81).
The aim was to quantify macromolecular interactions between specific biopolymers and stainless steel, combining modelling and shear-flow-induced detachment of functionalized microbeads in adhesive contact with bare or BSA-coated surfaces.Spherical microbeads functionalized with two types of chemical groups (NH2, OH) were chosen as a simplified bacterial model, in order to elucidate the role of macromolecular interactions between specific biopolymers and 316L stainless steel, in the frame of biofilm formation in the marine environment. NH2 microbeads were used in their native form or after covalent binding to BSA or different representative poly-amino acids. OH microbeads were used in their native form. Adhesion force between microbeads and bare or BSA-coated stainless steel was quantified at nanoscale. Shear-flow-induced detachment experiments were combined with a simplified version of a theoretical model, based on the balance of hydrodynamic forces and torque exerted on microbeads. A maximal adhesion force of 27.6 ± 8.5 nN was obtained for BSA-coated NH2 microbeads. The high reactivity of OH functional groups was assessed (adhesion force of 15.6 ± 4.8 nN for large microbeads). When charge-conducting stainless steel was coated with BSA, adhesion force was significantly lower than the one estimated with the bare surface, probably due to an increase in hydrophilic surface properties or suppression of charge transfer. The mechanism for microbead detachment was established (mainly rolling). The flow chamber and the associated theoretical modelling were demonstrated to be a relevant approach to quantify nanoscale forces between interacting surfaces.
Keywords: Adhesion force; Functionalized microbead; Stainless steel; Hydrodynamic method; Detachment; Modelling;
Cationic–anionic vesicle templating from fluorocarbon/fluorocarbon and hydrocarbon/fluorocarbon surfactants by Vivian A. Ojogun; Hans-Joachim Lehmler; Barbara L. Knutson (82-91).
Catanionic vesicles with mixed hydrocarbon/fluorocarbon bilayers and full fluorocarbon bilayers used in synthesis of silica hollow spheres by templating.Spontaneous catanionic vesicle formation is studied in systems comprising fluorinated surfactants, the cationic/anionic fluorinated surfactant system of 1,1,2,2-tetrahydroperfluorododecylpyridinium chloride (HFDPC)/sodium perfluorooctanoate (SPFO) and the analogous mixed hydrocarbon/fluorocarbon surfactant system of cetylpyridinium bromide (CPB)/SPFO. Aggregate formation is explored in the anionic-rich surfactant system (weight fraction of anionic surfactant, γ = 0.66–0.85) and a total surfactant concentration range of 0.1–2% wt/wt for the fluorinated system and 0.4–2.2% wt/wt for the mixed hydrocarbon/fluorocarbon system. Vesicle sizes range from approximately 40 to 200 nm for CPB/SPFO, as determined by negative staining transmission electron microscopy (TEM) and confirmed by dynamic light scattering. The primary vesicle diameter observed by TEM in the catanionic fluorinated/fluorinated surfactant system is smaller (20–50 nm). However, the relatively few larger vesicles (⩾100 nm) in the HFDPC/SPFO system dominate the dynamic light scattering measurements. Successful templating of silica hollow spheres is demonstrated in both HFDPC/SPFO and CPB/SPFO vesicle systems, using tetramethoxysilane (TMOS) as the silica precursor for the acid-catalyzed synthesis. The size of the resulting hollow silica particles is consistent with the templating of vesicles of the size range observed by TEM. Changes in zeta potential are used to monitor colloidal stability. At the conditions investigated (TMOS/surfactant weight ratios of 0.25–1.0, pH 3), the colloidal silica particles templated from fluorinated HFDPC/SPFO vesicles are more stable than the particles templated from the corresponding mixed fluorinated CPB/SPFO system. Further improvement of the stability of the colloidal particles is achieved in the CPB/SPFO systems by titrating the acid synthesis solution with base over the course of the particle synthesis.
Keywords: Catanionic vesicles; Fluorinated surfactants; Silica; CPB; SPFO; HFDPC;
Effective interactions in polydisperse colloidal suspensions investigated using Ornstein–Zernike integral equations by P. Bryk; M. Bryk (92-98).
Effective interactions between two big colloidal particles (yellow) mediated by smaller polydisperse colloidal particles (red).We present a mean of calculating the effective interactions in polydisperse colloidal suspension from liquid state integral equation theory. The method is based on Lado’s expansion of correlation functions in a suitable set of orthogonal polynomials. The outlined approach is subsequently used to investigate the effects of polydispersity on the effective potentials for model systems with attractive and repulsive bare interactions. The dominant effect of polydispersity of the smaller species is to weaken the effective potentials between big colloidal particles. This can be exploited as another way of tuning the interactions in colloidal suspensions to match the desired properties.
Keywords: Colloids; Effective interactions; Depletion; Polydispersity; Theory;
Biomimetic synthesis of copolymer–silica nanoparticles with tunable compositions and surface property by Xiaoqing Li; Tingting Yang; Qing Gao; Jianjun Yuan; Shiyuan Cheng (99-104).
Inspired by natural silicification, well-defined copolymer–silica nanoparticles with tunable sizes, compositions and surface zeta potentials were synthesized by using linear polyamines as mediators in water and under ambient conditions.We report using cationic poly(acrylamide-co-2-(dimethylamino) ethyl methacrylate, methyl chloride quaternized) (poly(AM-co-DMC)) to mediate biomimetic synthesis of hybrid copolymer–silica nanoparticles under ambient conditions. Poly(AM-co-DMC)s with various mole contents of DMC were prepared by solution copolymerization in water. Silicification was achieved by simply stirring a mixture of tetramethyl orthosilicate and an aqueous poly(AM-co-DMC) solution at room temperature for 30 min. Copolymers–silica hybrid nanoparticles were characterized with transmission electron microscopy (TEM), FT-IR spectroscopy, 1H NMR, thermogravimetry and aqueous electrophoresis. TEM studies indicated that the hybrid nanoparticles have well-defined spherical morphology and relatively narrow polydispersity with diameters of less than 50 nm. The compositions and zeta potentials of hybrid nanoparticles could be controlled by simply adjusting compositions of copolymers and solution conditions for silica mineralization. Due to the tunable compositions and surface zeta potentials, these new particles would be expected to have potential applications for controlled delivery, therapeutics and bioimaging.
Keywords: Polyamines; Silica nanoparticles; Biomimetic synthesis;
Use of wide-angle X-ray diffraction to measure shape and size of dispersed colloidal particles by S. Junaid S. Qazi; Adrian R. Rennie; Jeremy K. Cockcroft; Martin Vickers (105-110).
Width of the diffraction peaks are used to determine the size and the shape of the particle in a colloidal dispersion.Laboratory X-ray diffraction is used to investigate the size and shape of dispersed plate-like and spherical colloidal particles. Analysis of the wide-angle diffraction data provides information about the size and shape of crystals from the width of the Bragg peaks according to the Debye–Scherrer formula. The measurements, data analysis, and evaluation are discussed. It is shown that X-ray diffraction with conventional laboratory equipment on dispersed particles is feasible as a tool to determine both particle size and shape. Data for two samples – gold colloids and nickel (II) hydroxide particles are presented. The advantages and limitations of the method are discussed. X-ray diffraction measurements that are made in combination with dynamic light scattering can be used to estimate the thickness of stabilizing layers of polymers.
Keywords: Size determination; Shape analysis; X-ray diffraction; Gold particles; Nickel hydroxide colloids;
Development of novel composite membranes using quaternized chitosan and Na+-MMT clay for the pervaporation dehydration of isopropanol by Santosh K. Choudhari; Mahadevappa Y. Kariduraganavar (111-120).
This study demonstrates the preparation of novel composite membranes using Na+-MMT clay and quaternized chitosan. Clay establishes the electrostatic interaction with quaternary ammonium groups and protonated amino groups of chitosan, resulting in an excellent separation performance.Novel polymer–clay-based composite membranes were prepared by incorporating sodium montmorillonite (Na+-MMT) clay into quaternized chitosan. The resulting membranes were characterized by Fourier transform infrared spectroscopy (FTIR), wide-angle X-ray diffraction (WXAD), and thermogravimetric analysis (TGA). The effect of membrane swelling was studied by varying the water concentration in the feed. The membranes were employed for the pervaporation dehydration of isopropanol in terms of feed composition and Na+-MMT clay loading. The experimental results demonstrated that membrane containing 10 mass% of Na+-MMT clay showed the highest separation selectivity of 14,992 with a flux of 14.23 × 10−2 kg/m2 h at 30 °C for 10 mass% of water in the feed. The total flux and flux of water are found to be overlapping each other particularly for clay-incorporated membranes, signifying that the composite membranes developed in the present study involving quaternized chitosan and Na+-MMT clay are highly selective toward water. From the temperature-dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The resulting activation energy values obtained for water permeation ( E pw ) are much lower than those of isopropanol permeation ( E pIPA ) , suggesting that the developed composite membranes have higher separation efficiency for the water–isopropanol system. The estimated E p and E D values ranged between 8.97 and 11.89, and 7.56 and 9.88 kJ/mol, respectively. The positive heat of sorption ( Δ H s ) values were obtained for all the membranes, suggesting that Henry’s mode of sorption is predominant in the process.
Keywords: Chitosan; Na+-MMT clay; Isopropanol; Pervaporation; Selectivity; Activation energy;
Polyvinyl alcohol as the barrier layer in thin film composite nanofiltration membranes: Preparation, characterization, and performance evaluation by J.M. Gohil; P. Ray (121-127).
PVA TFC nanofiltration membranes show preferential rejection ability towards bi and monovalent salts.The present paper describes the preparation, characterization, and performance evaluation of thin film composite (TFC) nanofiltration (NF) membranes having porous polysulfone as base support and polyvinyl alcohol (PVA, degree of hydrolysis 86–87% and molecular weight 125,000) as the final barrier layer. Maleic acid (MA) was used as the cross-linker of PVA. The membranes were characterized by their molecular weight cutoff, FTIR, SEM, and contact angle. The effects of variation of different parameters like concentration of polysulfone, polyvinyl alcohol, maleic acid, and cure time on the membrane performance (flux and rejection of inorganic salts) were studied and the optimum membrane composition was evaluated. From the analysis of flux and rejection data it may be concluded that membranes prepared from 17% PSF, 1% PVA, with MA solution concentration of 0.2% (w/w) cured at a temperature of 125 ± 2 °C for 30 min give the optimum balance of flux and rejection (R). Such membranes show differential rejection among the sulfate and chloride salts. For membranes prepared under optimum conditions the average rejections of NaCl and MgSO4 are 22.8% and 83.8%, respectively; i.e., on an average 60% difference exists between the rejection of MgSO4 and NaCl. The overall trend of rejection by such membranes is R Na 2 SO 4 > R MgSO 4 > R NaCl > R CaCl 2 ≅ R MgCl 2 (R = rejection). The average MWCO of these membranes varies between 250 and 350 Da.
Keywords: Thin film composite NF membrane; Polyvinyl alcohol; Maleic acid; Flux; Preferential salt rejection;
Aging of nanocarbons in ambient conditions: Probable metastability of carbon nanotubes by Liangcheng Yang; Pyoungchung Kim; Harry M. Meyer; Sandeep Agnihotri (128-134).
Spectroscopic evidence of surface oxygen (automatically rejected) by SWNTs as they aged in ambient conditions for up to 15 monthsWe studied the physicochemical properties of several commercially available single- and multi-walled carbon nanotubes (SWNTs and MWNTs) and fullerenes stored in normal ambient conditions for 24 months. We found that SWNTs exhibit a trend of decreasing surface area and pore volume up to 7–15 months but then stabilized, no longer being impacted by sample age or outgassing temperatures. Using X-ray Photoelectron Spectroscopy, we also observed a trend of decreasing surface oxygen in all samples from the beginning with much lower % oxygen observed after 12–15 months of aging under ambient conditions. The surface oxygen then stabilized for the duration of this study. There was also evidence that the total structural-defect concentration, estimated from Raman spectroscopy, was somehow lowered during the aging process. The decrease in surface oxygen is an unexpected phenomenon because most other carbons, such as activated carbons or carbon molecular sieves, either oxidize or remain unaffected by age. We believe that nanocarbons are meta-stable materials (in pseudo-thermodynamic equilibrium), and that their aging in ambient conditions makes them more thermodynamically stable with fixed properties. This new information about the properties of nanocarbons should be further explored as it can help resolve some of the conflicting reports such as those about the environmental impacts of nanomaterials.
Keywords: Environment; Impacts; Aging; Nanocarbons; Chemistry; Surface area; Self-repairing; Carbon nanotubes;
Electrostatic and electrokinetic effects on hindered convection in pores by Panadda Dechadilok; William M. Deen (135-144).
Flow-induced distortion of the doublelayer increases the drag on a sphere.The sieving of macromolecules in ultrafiltration is affected by solute and pore charge, as well as size. A large, relatively rigid molecule such as a globular protein may be viewed as a particle in an electrolyte solution. Charge may influence both its equilibrium partition coefficient and its lag coefficient (G), which is the ratio of particle to fluid velocity. Partitioning had been examined previously for spheres in cylindrical pores by using continuum double layer theory to evaluate the electrostatic potential energy (E). The present objective was to estimate G for particles and pores of like charge. Particle or fluid motion tends to distort the diffuse double layers, an effect termed “relaxation,” which increases the drag on the particle. The streaming potential that arises from flow through a charged pore under open-circuit conditions also increases the drag on a confined, stationary particle. These electrokinetic effects were quantified using finite element solutions of the equations of motion, Poisson’s equation, and conservation equations for small ions in the electrolyte. It was found that charge effects generally reduce G, with relaxation tending to be the more important contributor. Thus, a freely suspended, charged particle will move through a pore more slowly than an uncharged one of the same size. However, the effects of E on sieving outweigh those of the electrokinetic decrease in G. That is, charge influences sieving mainly by altering the partition coefficient.
Keywords: Hindered transport; Streaming potential; Double-layer relaxation;
Interconnected porous epoxy monoliths prepared by concentrated emulsion templating by Jianli Wang; Zhongjie Du; Hangquan Li; Aimin Xiang; Chen Zhang (145-150).
The obtained porous monolith possessed high porosity with a complex network of channels and interconnected pores.Porous epoxy monoliths were prepared via a step polymerization in a concentrated emulsion stabilized by non-ionic emulsifiers and colloidal silica. A solution in 4-methyl-2-pentanon was used as the continuous phase, which contained glycidyl amino epoxy monomer (GAE), curing agent, and an emulsifier. An aqueous suspension of colloidal silica was used as the dispersed phase of the concentrated emulsion. After the continuous phase was completely polymerized, the dispersed phase was removed and a porous epoxy was obtained. An optimal HLB value of emulsifier for the GAE concentrated emulsion was determined. In addition, the morphology of the porous epoxy was observed by SEM. The effect of the colloidal silica, the emulsifier, the curing of the epoxy, and the volume fraction of the dispersed phase on the morphology of porous epoxy are systematically discussed.
Keywords: Porous; Epoxy; Monolith; Concentrated emulsion; Colloidal silica; Hydrophile–lipophile balance;
Effect of straight-chain alcohols on the physicochemical properties of calcium lignosulfonate by Xueqing Qiu; Mingfang Yan; Dongjie Yang; Yuxia Pang; Yonghong Deng (151-155).
The surface tension of the CL system decreases when straight-chain alcohols were added into CL aqueous solutions, and the decreasing level depends on the alkyl chain length of the alcohols.Lignosulfonate is an anionic surfactant from pulp processing industries. Alcohols are often used as cosurfactants in the application of surfactant. The improvement of straight-chain alcohols with different alkyl chain lengths as cosurfactant on the physicochemical properties of calcium lignosulfonate (CL) aqueous solution has been investigated. The results indicate that small amounts of straight-chain alcohols with longer alkyl chains are helpful in improving the surface activity of CL, especially when the number of carbon atoms in alcohols is 10 or larger. The adsorption amount of CL solutions with additives of longer chain alcohols on TiO2 particles increases greatly, and the zeta potential of TiO2 particles adsorbing CL rises significantly. It can be concluded that there is a cooperative effect of the longer chain alcohols on lignosulfonate to form a tighter adsorption layer at the interface. The steric hindrance increases with the increasing amount of adsorption, and the static repulsive force increases with the increasing zeta potential. Therefore, the effect of CL on the stability of the TiO2 suspension is enhanced dramatically by addition of longer chain alcohols. This understanding can lead to further development in expanding the functionalities of the lignosulfonate through manipulation of the adsorption capacity of CL on solid particles and enhance the dispersive ability of CL on solid suspensions by adding longer straight-chain alcohols.
Keywords: Calcium lignosulfonate; Straight-chain alcohols; Physicochemical properties; Adsorption; Zeta potential; Dispersive ability;
Synthesis and thermotropic liquid crystalline properties of zwitterionic gemini surfactants containing a quaternary ammonium and a sulfate group by Tianhua Zhou; Jianxi Zhao (156-162).
Zwitterionic gemini surfactants consisting of a quaternary ammonium and a sulfate group (referred to as C m EOSAC n ) formed stable thermotropic smectic A liquid-crystalline phases.A homologous series of novel zwitterionic gemini surfactants, N,N-dimethyl-N-[3-(alkyloxy)-2-sulfate-propyl]-alkylammonium (referred to as C m EOSAC n ), were synthesized. One of the hydrophilic groups is a sulfate anion, and the other is an ammonium cation. Their thermotropic liquid crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature X-ray diffraction (XRD). The results were compared with those for bis(quaternary ammonium) gemini amphiphiles with counterions and catanionic surfactants without a spacer. The C m EOSAC n s were shown to display improved thermal stability and to form a stable smectic A liquid-crystalline phase over a wide temperature region (63 ± 0.5 °C), which can be attributed to weakening the interactions between the surfactant headgroups. The XRD data confirmed that the two chains of molecules were arranged in a cis configuration with respect to the extended N–CH2–CH–SO4 skeleton in both the solid lattice and the mesophases. In addition, the DSC results showed that the dissymmetry of the hydrophobic chains had a slight effect on the melting point and the clearing point of the C m EOSAC n compounds. The present investigation points the way to developing stable liquid crystalline materials using gemini-type surfactants.
Keywords: Zwitterionic gemini surfactants; Synthesis; Phase transition; Thermotropic liquid crystals;
Impediments to the accurate structural characterisation of a highly concentrated emulsion studied using NMR diffusion diffraction by Nirbhay N. Yadav; William S. Price (163-168).
PGSE NMR diffusion diffraction can be a rich source of information for characterising emulsions, however, detailed consideration of the method and analysis is needed for correct data interpretation.Pulsed gradient spin–echo (PGSE) NMR diffusion studies with subsequent analysis using the Gaussian phase distribution (GPD) approach have long been used to determine the structure of emulsions. With the increasing availability of spectrometers equipped with higher gradient strength generation capabilities it is possible to extend PGSE measurements to where diffusive diffraction effects become evident. However the GPD approach cannot predict these diffraction-like coherence features which can be a rich source of information. With appropriate modelling based on the short gradient pulse approximation (SGP) such coherence features can provide morphological characteristics such as pore size, tortuosity, and connectivity. Further, the deviation of coherence features from ideal cases can be used to elucidate additional features such as the polydispersity of emulsion droplets which is a fundamental and crucial physical characteristic that influences the emulsion stability, rheology, and functionality. In this study analysis of PGSE NMR diffusion diffraction coherence features using the multiple propagator matrix formalism extension of the SGP approach is used to study structural characteristics of a highly concentrated emulsion.
Keywords: Concentrated emulsion; Diffusive diffraction; Emulsion droplet size distribution; PGSE NMR; Polydispersity; Porous system; Restricted diffusion;
A concise analysis of the effect of temperature and propanediol-1, 2 on Pluronic F127 micellization using isothermal titration microcalorimetry by Kawthar Bouchemal; Florence Agnely; Armand Koffi; Gilles Ponchel (169-176).
In the present work ITC was successfully used as a sensitive research tool for examining the effect of temperature and propanediol-1,2 on micellization behavior of Pluronic F127 by determining the CMC and thermodynamic parameters of the micellization (ΔH mic, ΔG mic, ΔS mic, and ΔC p).This article aims to explore the possibility of using isothermal titration microcalorimetry (ITC) for the investigation of F127 micellization and to study the effect of temperature and addition of propanediol-1,2 on F127 micellization behavior. From this work, ITC proved efficient to be used as a tool for the determination of the critical micellization concentration (CMC) and the enthalpy of micellization (ΔH mic) of F127, from which the other thermodynamic parameters were calculated (free energy (ΔG mic), entropy (ΔS mic), and heat capacity of micellization (ΔC p,mic)). The micellization of F127 was confirmed to be a strongly endothermic process with predominance of hydrophobic interactions (TΔS mic > ΔH mic) and the correlation of enthalpy and entropy of micelle formation exhibits an excellent linearity. The temperature dependence of F127 micellization was revealed by using ITC, since the CMCs values were, respectively, 0.197, 0.095, 0.085, and 0.079 mM for temperatures 28, 29, 30, and 31 °C. Secondly, by the addition of propanediol-1,2 to the micellization medium containing 1.187 mM of F127, the CMC was shifted to lower values (0.095, 0.081, 0.077, 0.069 and 0.066 mM, respectively, for propanediol-1,2 concentrations of 0%, 1.4%, 2.3%, 2.8%, and 3.7% w/v in the micellization medium). Finally, ITC was used as diagnostic tool with the aim of checking the reproducibility of the experiments independently on the kinetic and the dynamic aspects related to the micelle formation breakup. However, in this work we proved that the use of ITC for the determination of the CMC and thermodynamic parameters associated with F127 micellization is limited to a range of temperatures when sigmoidal curves were obtained.
Keywords: Pluronic F127; Poloxamer 407; Block copolymer; Isothermal titration microcalorimetry; Critical micellization concentration; Micellization; Thermodynamics; Propanediol-1,2, dynamics;
Microstructures and rheological dynamics of viscoelastic solutions in a catanionic surfactant system by Haiqing Yin; Yiyang Lin; Jianbin Huang (177-183).
Microstructural transitions and rheological properties of viscoelastic solutions formed in a catanionic surfactant system were studied using a combination of rheology and dynamic light scattering.Viscoelastic solutions formed in a catanionic surfactant system of dodecyltriethylammonium bromide (DTEAB)/sodium dodecylsulfate (SDS) at the molar ratio of 27/73 were systematically studied using a combination of rheology and dynamic light scattering (DLS). Wormlike micelles began to form above the total surfactant concentration (C total) of 120 mM by the growth of small cylindrical micelles. Subsequently the system was found to exhibit linear viscoelasticity with characteristic of a Maxwell fluid in the intermediate concentration range of 170–210 mM, which arose from a 3D entangled network of wormlike micelles. At higher surfactant concentrations, a transition from linear micelles to branched structures probably took place. Finally and significantly, the effect of the surfactant headgroup on the rheological property of catanionic surfactant mixtures was discussed.
Keywords: Catanionic surfactant; Viscoelastic solution; Rheology; Wormlike micelles; Dynamic light scattering; Microstructure transition;
Influence of hydrophilic surfactants on the properties of multiple W/O/W emulsions by T. Schmidts; D. Dobler; C. Nissing; F. Runkel (184-192).
The distribution of emulsifiers in W/O/W multiple emulsions is described. The influence of hydrophilic emulsifiers on the emulsion stability is determined.Multiple W/O/W emulsions for topical application using Span 80 as a lipophilic emulsifier were prepared. Several hydrophilic emulsifiers were tested in respect of their suitability for the preparation of multiple emulsions. In addition, the effect of different oil-phase compositions on emulsion stability was investigated. The physicochemical parameters of the formulations were characterized and their long-term stability was evaluated by means of rheological measurements, droplet size observations and conductivity analysis.As discovered, the modification of an oil-phase composition results in a decrease in the diffusion coefficient of water and water-soluble substances and, consequently, in enhanced stability. The influence of the release of electrolytes from the inner to the outer water phase on the emulsion stability behaviour was investigated. It was found, that the effect of the hydrophilic emulsifiers on the formulation properties is related not only to its HLB value, but rather to its chemical composition.As a result, polyethoxylated ethers of fatty alcohols (C = 16–18) with HLBs between 15.3 and 16.2 appear to be the most suitable ones for creating stable formulations.
Keywords: W/O/W multiple emulsions; HLB; Hydrophilic surfactant; Viscosity; Electrolyte encapsulation;
Contact angle of a hemispherical bubble: An analytical approach by M.A.C. Teixeira; P.I.C. Teixeira (193-200).
Effect of gravity on the shape of a Plateau border around a soap bubble on a horizontal flat surface, found numerically (symbols) and analytically (lines).We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace’s equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity.
Keywords: Foams and emulsions; Contact lines;
Emulsification mechanism and storage instabilities of hydrocarbon-in-water sub-micron emulsions stabilised with Tweens (20 and 80), Brij 96v and sucrose monoesters by John V.L. Henry; Peter J. Fryer; William J. Frith; Ian T. Norton (201-206).
Comparison of ripening rate for a range of surfactants as a function of surfactant concentration and the starting droplet size.The influence of both the nature of the surfactant and surfactant concentration on the processes of droplet break-up and coalescence in the formation of decane-in-water nano-emulsions in a high-pressure homogenizer was investigated. Emulsions were produced using a Christison Scientific M110-S microfluidiser with an impinging jet high-shear chamber. For all six surfactants studied (Tween 20, Tween 80, Brij 96v, sucrose monolaurate, sucrose monomyristate and sucrose monopalmate), the droplet size decreased with increasing surfactant concentration reaching a limiting droplet size at a surfactant concentration of 15 mM. The limiting droplet size for the different surfactants used were; Tween 20 (∼250 ± 30 nm), Tween 80 (∼320 ± 40 nm), Brij 96v (∼200 ± 20 nm) and the three sucrose monoesters had very similar sizes of ∼250 ± 20 nm. A hydrophobic fluorescent dye (1-undecylpyrene) was used to establish the extent of competition between droplet break-up and coalescence in the emulsification process. For all the emulsifiers studied, droplet coalescence in the process reduced as the amount of emulsifier increased, becoming zero at concentrations of about 15 mM, i.e. the same concentration as that required to produce the limiting minimum droplet size. This shows that in the emulsification process droplet size is determined by both break-up and re-coalescence events, and at lower surfactant concentrations (<15 mM) that the final droplet size is probably a consequence of multiple break-up events. Emulsion stability over 200 h was investigated by measuring changes in the droplet size using dynamic light scattering. The increase in droplet volume was shown to be linear with respect to time, indicating an Ostwald ripening process. The observed ripening rate for the three sucrose monoesters (monopalmitate, monomyristate and monolaurate) was approximately 20 nm3 s−1, which is the ripening rate calculated using the Lifshitz–Slesov–Wagner (LSW) theory. This ripening rate is the change in radius that results from movement of the oil through the continuous phase, taking into account the oil solubility in water and the diffusion coefficient of the decane-in-water. The ripening rate for Brij 96v was about three times larger than the calculated rate and there is an indication that the ripening rate increases slightly with increasing surfactant concentration, indicating that some enhancement due to the presence of micelles has occurred. With Tween 80 and 20 the ripening rates were 20 and 40 times, respectively, larger than those calculated using the solubility and diffusion coefficients. The increased rate has been shown to be first order with respect to the surfactant concentration indicating micelle mediated ripening. It is hypothesized that an optimum formulation for the sub-micron emulsion with these types of surfactant, will balance surfactant concentration to minimize droplet size during processing while aiming to minimize or prevent Ostwald ripening.
Keywords: Mini-emulsion; Nano-emulsion; Emulsification; Impinging jets; Droplet break-up; Coalescence; Ostwald ripening;
Effects of glycols on the thermodynamic and micellar properties of TTAB in water by Amalia Rodrı´guez; Marı´a del Mar Graciani; Gaspar Fernández; Marı´a Luisa Moyá (207-215).
In this work the effects of glycol addition on the TTAB micellization, on the structure of TTAB micelles and on their characteristics as reaction media have been investigated.Aggregation of tetradecyltrimethylammonium bromide, TTAB, in mixed solvent systems containing ethylene glycol, EG, 1,2-propylene glycol, 1,2-PROP, 1,3-propylene glycol, 1,3-PROP, and tetraethylene glycol, TEG, has been investigated by employing conductivity and fluorescence methods. Gibbs energies of micellization were determined in order to evaluate the effects of the co-solvent on the aggregation process. Information about the influence of the organic solvent on the surfactant adsorption at the air-solution interface, on the micellar size and on the polarity of the micellar interfacial region was obtained by means of surface tension and fluorescence measurements. The study of the reaction methyl naphthalene-2-sulfonate + Br - in the water–glycol TTAB micellar solutions provided information about the characteristics of TTAB micelles as microreactors in the water–solvent binary mixtures.
Keywords: TTAB; Micellization; Ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; Tetraethylene glycol; Kinetics;
Temperature and salt-induced micellization of dodecyltrimethylammonium chloride in aqueous solution: A thermodynamic study by Bojan Šarac; Marija Bešter-Rogač (216-221).
Effect of NaCl on the enthalpic and self-association behavior of dodecyltrimethylammonium chloride at 298.15 K.Thermodynamics of micelle formation of the cationic surfactant dodecyltrimethylammonium chloride (DTAC) in water and aqueous NaCl solutions were investigated. Isothermal titration calorimetry (ITC) has been used to study the effect of the added NaCl on the critical micelle concentration, cmc, and enthalpy of micellization, Δ micHo , between 278.15 and 318.15 K. Gibbs free energy, Δ micGo , and entropy, Δ micSo , were deduced by taking into account the counterion binding. From the temperature dependence of Δ micHo the heat capacities of micellization, Δ mic c p o , were determined.NaCl shifts cmc strongly towards lower values, indicating the screening of the repulsions of the polar head groups by counterions; but it influences Δ micHo at higher concentrations of salt only.Δ micGo is always negative and slightly temperature dependent. The temperature dependence of Δ micSo indicates that the process of micellization is entropically driven. Δ micHo decreases strongly with increasing temperature and passes through zero (endothermic to exothermic processes). The temperature dependence of the critical micelle concentration exhibits a minimum characterized by Δ micHo = 0, where Δ micGo is of purely entropic contribution in all solutions. Δ mic c p o are strongly negative in all solvents, relating directly to the removal of water accessible non-polar surface of DTAC in the presence of excess counterions also.
Keywords: Dodecyltrimethylammonium chloride; Isothermal titration calorimetry; NaCl; Micellization; Critical micelle concentration; Thermodynamics of micelle formation;
Ferritin as a bionano-particulate emulsifier by Syuji Fujii; Atsushi Aichi; Masahiro Muraoka; Naoko Kishimoto; Kenji Iwahori; Yoshinobu Nakamura; Ichiro Yamashita (222-228).
Stable ‘Pickering-type’ emulsions were prepared using ferritin as a bionano-particulate emulsifier. Transmission electron microscopy studies confirmed the ferritin particles were adsorbed at the oil–water interface and stabilized the emulsions.Stable ‘Pickering-type’ emulsions were prepared using ferritin, a spherical protein, as a bionano-particulate emulsifier and n-dodecane, toluene, caster oil, olive oil or vegetable oil as an oil phase, in the absence of any surfactant molecules. All the emulsions prepared were of the oil-in-water type and an increase of ferritin concentration decreased the volume average droplet diameters. Transmission electron microscopy studies of the ferritin residues remaining after evaporation of oil and water from the emulsion revealed a broken capsule morphology, which is strong evidence for the attachment of ferritin at the oil–water interface thereby stabilizing the emulsion. The emulsion droplets could be elongated and made to pass through a glass capillary.
Keywords: Pickering emulsion; Particulate emulsifier; Ferritin; Emulsification; Soft capsule;
Synthesis and aqueous solution properties of novel anionic heterogemini surfactants containing a phosphate headgroup by Yuichiro Takamatsu; Naoyuki Iwata; Kazuyuki Tsubone; Kanjiro Torigoe; Takeshi Endo; Kenichi Sakai; Hideki Sakai; Masahiko Abe (229-235).
Physicochemical properties of novel anionic heterogemini surfactants containing a phosphate headgroup have been studied on the basis of static/dynamic surface tension, fluorescence, DLS and cryo-TEM data.The physicochemical properties of aqueous solutions of novel anionic heterogemini surfactants (POH-n-ODAm) have been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The surfactants are synthesized from oleic acid: the hydrocarbon chain (n = 6, 8 and 10) is covalently bound to the terminal carbonyl group and a phosphate headgroup is introduced to the cis double bond of an oleic acid derivative. The static surface tension and fluorescence measurements demonstrate that the critical aggregation concentration (cac) is decreased significantly with increasing hydrocarbon chain length, resulting from the increased hydrophobicity and the increased degree of dissymmetry of the surfactants. As is generally seen for gemini surfactants, the measured cac is much lower than that of the monomeric phosphate-type surfactant reported previously. At concentrations well above the cac, the heterogemini surfactants spontaneously form vesicular assemblies in bulk solution, which is confirmed with DLS and cryo-TEM measurements.
Keywords: Gemini surfactants; Phosphate; Surface tension; cryo-TEM; Adsorption; Molecular association;
Brownian dynamics simulations of a dispersion composed of two-types of spherical particles: For development of a new technology to improve the visibility of rivers and lakes by Akira Satoh; Eiji Taneko (236-242).
Adsorption agents (large particles) adsorb many suspended substances (small particles) and sediment gradually toward the bottom in the gravity filed.We have carried out Brownian dynamics simulations of sedimentation phenomena of a dispersion composed of two-kinds of spherical particles under the gravity field. This study may be the first step to develop a new technology which enables us to improve the visibility of rivers and lakes. In the present study, we have modeled sub-micrometer-dimension particles, or dirty particles, as small spherical particles, and capturing particles as large spherical particles; these two-kinds of particles conduct Brownian motion in water, and large particles adsorb small particles to sediment gradually toward the bottom in the gravity field. From the results of simulations, the influences of Brownian motion, the size of each particle, and the gravity force on the performance of the adsorption of large particles have been discussed. In addition, we have discussed what the most appropriate situation of large particles is to accomplish the most effective adsorption rate or improve the visibility of water most effectively in terms of capturing particles. The most important conclusion derived from the present results is that, in order to improve the capturing performance, the Brownian motion of large particles has to be activated in an appropriate number density without losing the influence of the gravity.
Keywords: Water purification; Porous absorbent; Suspended substance; Sedimentation phenomena; Brownian dynamics simulation;
Nonlinear electrokinetic phenomena around nearly insulated sharp tips in microflows by Yuval Eckstein; Gilad Yossifon; Avraham Seifert; Touvia Miloh (243-249).
Microparticle imaging velocimetry measurements of the nonlinear electrokinetic flow around nearly insulated sharp tips/corners within microfluidic channels were compared to theoretical predictions.This contribution seeks to provide for the first time a combined comprehensive theoretical prediction and quantitative experimental (microparticle imaging velocimetry – μ -PIV) measurements of the nonlinear electrokinetic flow around sharp tips in order to substantiate former theoretical and qualitative experimental flow visualization results [S.K. Thamida, H.C Chang, Phys. Fluids 14 (2002) 12; P. Takhistov, K. Duginova, H.C. Chang, J. Colloid Interface Sci. 263 (2003) 133; G. Yossifon, I. Frankel, T. Miloh, Phys. Fluids 18 (2006) 117108]. The study focuses on two microchannel designs: an L-shaped channel and two isolated tips in a straight channel, important in engineering for mixing and particle-trapping purposes. The new experimental results were explained in terms of an induced-charge electrokinetic mechanism alone, without the concentration polarization mechanism as suggested by earlier studies. The vortex generation phenomenon around corners was explained in terms of the varying ratio between the equilibrium and the induced-charge zeta-potentials, showing fair qualitative agreement between numerical and experimental results. Hence, a transition from an irrotational to nonlinear-dominated flow with a vortex pattern occurs beyond a certain electric-field threshold. In particular, for the L-shaped channel case, it is demonstrated that beyond a second field threshold an upstream vortex appears in addition to the downstream one.
Keywords: Induced-charge electroosmosis; Microfluidics; Electrokinetic flow; Vortex; Sharp tip; Polarization;
The effect of surface charge distribution on hindered diffusion in pores by Ronald J. Phillips (250-260).
A charged solute diffuses through a charged, cylindrical pore that is filled with aqueous solution. The electrostatic potential on the pore wall oscillates about a mean value.An analytic solution is derived for the hindered diffusion of charged, small solutes in charged, cylindrical pores in which the pore wall potential consists of the sum of an average and an oscillatory component. When the oscillatory contribution is absent, the effect of electrostatic interactions on diffusion is negligible. However, when the wall potential or surface charge density varies axially, electrostatic interactions hinder the rate of diffusion significantly, and can stop it completely if “choke points” develop where the solute concentration becomes zero. The degree of hindrance is generally weaker when the electrostatic charge on the pore wall and the charge on the solute have the same signs, leading to a repulsion, than it is in the presence of an attraction. The electrostatic hindrance is also affected by the length scale of the axial variation along the pore wall, becoming stronger as that length grows, until an asymptotic value is reached. The theory for the effect of variations of the electrostatic potential on rates of diffusion is shown to be in good agreement with experimental data taken from the literature. The results here are obtained by using generalized Taylor dispersion theory, and are therefore rigorous predictions of what occurs over times long enough that the solute diffuses through a tube many times longer than a single periodic cell. The electrostatic interactions are calculated using the linear Poisson–Boltzmann equation.
Keywords: Hindered diffusion; Electrostatic interaction; Polymer gel;
Shear induced structure additives and nonlinear pressure drop effects in permeable flow by David Spain; Sebastiaan Troost; Michael Golombok (261-265).
Three profiles for flow through an oil reservoir of varying permeability. 1 is the desired profile, 2 the real profile, 3 using this study.In classical flow through permeable rock, the pressure drop is linearly distributed through the medium. Shear induced structure materials, surfactant/co-solute pairs, were added to retard flow in higher permeability rock samples. A novel core holder allows the axial pressure distribution along the flow direction to be measured. This enables the pressure drop to be measured as a function of distance along the core. The results show the spatial scale and the effect on pressure distribution associated with varying concentrations of shear induced structure additives. Subsequent flushing with water leads to restoration of the original flow level. The rate of recovery is dependent on the pressure of flushing which determines shear – showing that break up of the shear induced structure materials deposited in the porous rock is also dependent on shear.
Keywords: Permeable flow; Oil and gas; Shear induced structures; Shear effects;
Mono-distributed single-walled carbon nanotube channel in field effect transistors (FETs) using electrostatic atomization deposition by D.W.H. Fam; A.I.Y. Tok (266-269).
The agglomeration of Carbon Nanotubes was reduced via electrostatic atomization and a Schottky junction was formed easily.This communication reports on the novel work of creating a transistor channel based on functionalized single-walled carbon nanotubes (SWNTs) via electrostatic atomization deposition. The current method of drop-cast though convenient was unable to produce replicable transistor device due to its inherent inability in controlling the volume of liquid being drop-cast. Hence, this method of electrostatic atomization was introduced to consistently obtain a uniformly distributed SWNT channel resulting in a good transistor device.
Keywords: Carbon nanotubes; Electrostatic atomization; Monodispersed;
AgCl and Ag/AgCl hollow spheres based on self-assemblies of a multi-amine head surfactant by Wei Wang; Wensheng Lu; Long Jiang (270-275).
Micelles of the surfactant C18N3, dispersed in HCl solution, can be transformed to stable and stiff AgCl hollow spheres with diameters ranging from 100 nm to 1200 nm by addition of AgNO3.A simple method for fabricating Ag/AgCl hollow spheres was developed by using a multi-amine head surfactant C18N3 as a soft template. After adding AgNO 3 to micelles of C18N3 dispersed in HCl solution, Ag/AgCl hollow spheres were formed with diameters ranging from 100 nm to 1200 nm which were a function of aging time. The mechanical strength of the formed spheres was found to be very good, probably due to the uniquely structured C18N3 surfactant as well as the reinforcement effect of Ag/AgCl on the NH 2 terminal groups. The active species on the surfaces of hollow spheres, Ag + and Cl - , remained almost unchanged when exposed to natural daylight for more than 1 year, showing a very good stability against light and environmental reduction. However, the obtained Ag+ species on the surface could be transformed into Ag 0 quickly with high yield (ca. 90%) under UV light irradiation. The transfer process was studied by EDX spectra at different irradiation times. Thus the Ag/AgCl hollow spheres may serve as useful precursors for many other noble metallic hollow spheres because Ag could be replaced by other noble metals such as Au and Pt with the aid of the galvanic replacement reaction.
Keywords: Ag/AgCl; Hollow spheres; Surface chelation; Multi-amine head surfactant; Photo-reduction;
Structure of a polyelectrolyte around an electronically responsive cylinder by Chongbo Sun; Tian Tang (276-283).
Wrapping geometry of a polyelectrolyte around a cylinder depends on the response of the cylinder.The structure of a polyelectrolyte (PE) around a rigid cylinder is studied by considering the electrostatic and van der Waals interactions between them. The PE is represented by a helix of discrete charges. The cylinder core is allowed to be conducting or dielectric and responds to the external charges electronically. Approximating the cylinder surface locally as a half space, the electrostatic free energy of the PE–cylinder complex is obtained in closed form by solving the Debye–Hückel equation. We show that the competition between the van der Waals adhesion and the electrostatic repulsion between charges can result in an optimal wrapping geometry. The dependence of the optimal geometry on the salt concentration of the solution is demonstrated to be sensitive to the nature of the cylinder. In particular, it is shown that the salt concentration has a strong influence on the optimal geometry for a dielectric cylinder, while it hardly affects that for a conducting cylinder.
Keywords: Polyelectrolyte; Debye–Hückel equation; Electrostatic interaction; Van der Waals interactions; Optimal wrapping geometry;
Combined DFT and IR evidence on metastable-equilibrium adsorption of arsenate on TiO2 surfaces by Meiyi Zhang; Guangzhi He; Gang Pan (284-286).
Arsenate addition mode changed microscopic structure for equilibrium adsorption samples under same thermodynamic conditions.Adsorption of arsenate on TiO2 surfaces under the same total mass and thermodynamic conditions reached to different final equilibrium states when the reaction was conducted through different pathways. The microscopic structure for equilibrium adsorption samples were significantly affected by the way arsenate was added to the TiO2 suspension (e.g. 1-batch or multi-batch). The As–OTi asymmetric stretching vibration of 3-batch samples shifted to lower wavenumbers by 15 cm−1 than that of 1-batch samples. Combined analysis of ATR-FTIR spectroscopy and DFT calculation indicated that the change of reaction pathway altered the ratio of double-corner complex to single-corner complex and, hence, the real equilibrium state that is a mixture of the two surface complexes.
Keywords: Thermodynamics; Reaction kinetics; ATR-FTIR spectroscopy; DFT calculation; Vibration mode shift;
Comparison of gas–solid chromatography and MM2 force field molecular binding energies for greenhouse gases on a carbonaceous surface by Thomas R. Rybolt; Kevin T. Bivona; Howard E. Thomas; Casey M. O’Dell (287-292).
Molecule–surface binding energies were calculated from molecular mechanics (side view of dichlorodifluoromethane on the carbon surface surface model) and compared to experimental values from van’t Hoff plots.Gas–solid chromatography was used to determine B 2s (gas–solid virial coefficient) values for eight molecular adsorbates interacting with a carbon powder (Carbopack B, Supelco). B 2s values were determined by multiple size variant injections within the temperature range of 313–553 K. The molecular adsorbates included: carbon dioxide (CO2); tetrafluoromethane (CF4); hexafluoroethane (C2F6); 1,1-difluoroethane (C2H4F2); 1-chloro-1,1-difluoroethane (C2H3ClF2); dichlorodifluoromethane (CCl2F2); trichlorofluoromethane (CCl3F); and 1,1,1-trichloroethane (C2H3Cl3). Two of these molecules are of special interest because they are “super greenhouse gases”. The global warming potential, GWP, for CF4 is 6500 and for C2F6 is 9200 relative to the reference value of 1 for CO2. The GWP index considers both radiative blocking and molecular lifetime. For these and other industrial greenhouse gases, adsorptive trapping on a carbonaceous solid, which depends on molecule–surface binding energy, could avoid atmospheric release. The temperature variations of the gas–solid virial coefficients in conjunction with van’t Hoff plots were used to find the experimental adsorption energy or binding energy values (E *) for each adsorbate. A molecular mechanics based, rough-surface model was used to calculate the molecule–surface binding energy (Ecal*) using augmented MM2 parameters. The surface model consisted of parallel graphene layers with two separated nanostructures each containing 17 benzene rings arranged in linear strips. The separation of the parallel nanostructures had been optimized in a prior study to appropriately represent molecule–surface interactions for Carbopack B. Linear regressions of E * versus Ecal* for the current data set of eight molecules and the same surface model gave E * = 0.926Ecal* and r 2=0.956. A combined set of the current and prior Carbopack B adsorbates studied (linear alkanes, branched alkanes, cyclic alkanes, ethers, and halogenated hydrocarbons) gave a data set with 33 molecules and a regression of E * = 0.991Ecal* and r 2=0.968. These results indicated a good correlation between the experimental and the MM2 computed molecule–surface binding energies.
Keywords: Henry’s law adsorption; Gas–solid virial coefficients; Molecular mechanics; Adsorption energy; Molecule–surface binding energy; Greenhouse gases;
Comment on “An analytic solution of capillary rise restrained by gravity” by N. Fries and M. Dreyer by D.A. Barry; L. Wissmeier; J.-Y. Parlange; G.C. Sander; D.A. Lockington (293-295).
The Lambert W function, which appears in the solution of the Green and Ampt model of capillary rise.The porous medium model of Green and Ampt, describing flow in porous media, appeared earlier than the capillary model of Washburn, although both lead to mathematically identical models. Here, the model of Green and Ampt was related to the Washburn model by an examination of the parameters involved in each. Fries et al. [N. Fries, M. Dreyer, J. Colloid Interface Sci. 320 (2008) 259–263] presented an explicit solution to this model. This solution is identical to the explicit solution of the Green and Ampt model presented earlier by Barry et al. [D.A. Barry, J.-Y. Parlange, G.C. Sander, M. Sivaplan, J. Hydrol. 142 (1993) 29–46].
Keywords: Green and Ampt; Capillary rise; Porous media; Lambert W function; Analytical solution;
On the pinning of interfaces on micropillar edges by J. Berthier; F. Loe-Mie; V.-M. Tran; S. Schoumacker; F. Mittler; G. Marchand; N. Sarrut (296-303).
Modeling of the pinning of an interface on rounded edged micropillars. The pinning is less effective and depends on the curvature radius of the edges.Microsystems for biotechnology often make use of pillars to perform the targeted microfluidic functions. In many cases the role of the pillars is to block or maintain fixed an interface between two immiscible fluids. This phenomenon is usually called pinning. The pining principle is used for capillary valves, liquid–liquid extraction devices, etc. It is common to estimate the pinning efficiency by considering mathematically perfect edges. In reality, microfabricated edges always show some smoothness that can be modeled by a small curvature radius. In this work, we investigate the pinning on square, circular, triangular, and diamond-shaped pillars, and analyze the anchoring on the upstream edges (first pinning conditions) and possibly on the downstream edges (second pinning conditions). It is shown that pinning efficiency decreases very quickly with the curvature radius of the pillar edge. It is concluded that the quality of the microfabrication is essential. Especially oxidation of the silicon reduces considerably the pinning efficiency. Moreover, it is shown that square pillars pin better an interface than triangular pillars. For triangular pillars, a pillar angle—angle between two facets—optimal for pinning has been determined that depends on the quality of microfabrication.
Keywords: Interface; Pinning; Pillar; Canthotaxis; Laplace law;
Photocatalytic activity of a surface-modified anatase and rutile titania nanoparticle mixture by Seonmin Kim; Sheryl H. Ehrman (304-307).
Increased photoactivity of mixed anatase and rutile titania nanoparticles was observed after capillary condensation of tetraethyl orthosilicate (TEOS) onto the particles, followed by reaction of TEOS to form silica.Photocatalytic activity of mixtures of anatase and rutile titania nanoparticles, both bare and treated via capillary condensation of a silica precursor, was investigated by following photodegradation of methylene blue by ultraviolet light in an aqueous solution. The best observed activity for the physically mixed nanoparticles was seen at an anatase to rutile mass ratio of 4:1. This mixture was subject to capillary condensation of tetraethyl orthosilicate (TEOS) at various saturation ratios, followed by reaction of TEOS to form silica. Treatment at a saturation ratio of 1.2 improved photoactivity over that of the physical mixture, a result attributed to enhanced interphase connectivity and increased methylene blue adsorption onto silica.
Keywords: Titania; Anatase; Rutile; Silica; Photocatalytic activity; Capillary condensation;
Differential scanning calorimetric study of nonionic surfactant mixtures with a room temperature ionic liquid, bmimBF4 by Tohru Inoue; Yuka Higuchi; Takeshi Misono (308-311).
A Krafft point phenomenon is observed in solutions of nonionic surfactants in a room temperature ionic liquid, bmimBF4, contrary to the case of normal aqueous solutions.The melting behavior of polyethyleneglycol dodecyl ethers (C12E6, C12E7, and C12E8) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), was investigated by means of differential scanning calorimetry (DSC). The melting temperature as a function of the surfactant concentration, combined with the cmc curve and cloud point curve, provided phase diagrams for the surfactant/bmimBF4 mixtures in solvent-rich region. The characteristic feature of the mixtures is an existence of the Krafft temperature which is usually not observed with aqueous solutions of nonionic surfactants. The heat of fusion as a function of the surfactant concentration provided the interaction energy between the surfactant and bmimBF4. The interaction energy shows a linear dependence on the length of polyoxyethylene (POE) chain of the surfactants, which suggests that the solvation takes place around the POE chain.
Keywords: Nonionic surfactant; Room temperature ionic liquid; Phase diagram; Krafft point; Surfactant–ionic liquid interaction; Differential scanning calorimetry;
Determination of micelle diffusion coefficients with fluorescence correlation spectroscopy (FCS) by Franziska Luschtinetz; Carsten Dosche (312-315).
Normalized correlation funtion G(τ) of BPEA in Tween 20 at different surfactant concentrations and the FCS curve of the reference dye rhodamine 6G in water.In our study we determined the diffusion coefficient of Tween 20 micelles at different surfactant concentrations (10−4–10−2 M) via fluorescence correlation spectroscopy. The hydrophobic fluorescent dye 9,10-bis(phenylethynyl)anthracene, located in the micellar phase, was used as marker for the diffusion of Tween 20 micelles. The hydrodynamic radius of the micelles, R h, was estimated from the diffusion coefficient and compared with literature values from previous studies.
Keywords: Tween 20; Fluorescence correlation spectroscopy; BPEA; Diffusion coefficient; Nonionic surfactants;
Electrokinetic potentials of Al2O3 in concentrated solutions of metal sulfates by Marek Kosmulski; Piotr Prochniak; Jarl B. Rosenholm (316-318).
ζ Potentials of Al2O3 in concentrated MgSO4 solutions.The zeta potentials of alumina (10% by mass dispersions) in 0.1–1 M solutions of metal sulfates were determined by means of the electroacoustic method. The background correction was used to account for the electroacoustic signal of the electrolyte. The zeta potentials in the solutions of alkali sulfates were in the range from −8 to −19 mV. They were rather insensitive to the pH (4–9.5), and to the nature and concentration of the salt. In MgSO4 solutions (0.05–0.5 M, pH 4–8), the zeta potentials were also negative (−3 to −9 mV) showing the preference of alumina to adsorb sulfate anions rather than magnesium cations.
Keywords: Electrokinetic potential; Concentrated electrolyte solutions; Specific adsorption; Electroacoustic method;
Synthesis and characterization of Prussian blue@platinum nanoparticle hybrids from a mixture solution of platinum nanocatalyst and ferric ferricyanide by Jia Zhang; Wen Yang; Hui Zhu; Jing Li; Fan Yang; Bailin Zhang; Xiurong Yang (319-324).
An interconnected network of nanoclusters has been prepared from reacting platinum nanoparticles with ferric ferricyanide. Spectroscopic studies show a dominance of Prussian blue and a minority of Prussian blue analogue, platinum ferricyanide, in the nanoclusters.In the present study, platinum nanoparticles modified with Prussian blue (PB) have been synthesized by a heterogeneous catalytic reaction. Transmission electronic microscopy (TEM) confirmed the deposition of nanoclusters around the surfaces of platinum particles, and spectroscopic studies verified that the molecular composition of the nanoclusters was dominantly PB and a minority of platinum ferricyanide. Thus, it was shown that the platinum particles behaved not only as catalysts for the growth of PB, but also as a reactant to generate a PB analogue complex. Moreover, potassium was not detected in the final product, demonstrating that the molecular nature of PB was in the “water-insoluble” form, Fe 4 3 + [ Fe II ( CN ) 6 ] 3 .
Keywords: Prussian blue; Platinum nanoparticles; Catalysis; Platinum ferricyanide;
by Arthur Hubbard (325).
Joseph Alfred Kitchener (1916–2009) by Robert J. Pugh; John Ralston (326-327).