Journal of Colloid And Interface Science (v.315, #2)
Adsorption properties of tea polyphenols onto three polymeric adsorbents with amide group
by Jianhan Huang; Kelong Huang; Suqin Liu; Qiong Luo; Mancai Xu (pp. 407-414).
Macroporous crosslinked poly( N-methyl- N- p-vinylbenzylacetamide) (PMVBA), poly( N-methyl- N- p-vinylbenzylurea) (PMVBU), and poly( N-methylacrylamide) (PMA) were prepared and their adsorption behaviors for tea polyphenols (TP) were investigated in aqueous solution. The results indicated that their adsorption capacities for TP followed an order as: PMVBU>PMVBA>PMA. The adsorption isotherms were fitted to Freundlich isotherm and adsorption enthalpies were calculated. It was found that Freundlich isotherm was suitable to characterize the adsorption process and their adsorption enthalpies for TP gave the same order as: PMVBU>PMVBA>PMA. Surface energy heterogeneity was analyzed by Do's model and the surface of PMVBU was shown to be the most homogeneous. Analysis of adsorption mechanism suggested that multiple hydrogen bonding, hydrophobic interaction, andπ–π stacking were responsible for the adsorption of TP onto the adsorbents.Adsorption isotherms of TP onto (a) PMVBA, (b) PMVBU, and (c) PMA adsorbents from aqueous solution at five different temperatures: 293, 298, 303, 308, and 313 K, respectively.
Keywords: Polymeric adsorbent; Tea polyphenols; Adsorption; Hydrogen bonding; Hydrophobic interaction; π; –; π; stacking
Carbonate adsorption on goethite in competition with phosphate
by Rasoul Rahnemaie; Tjisse Hiemstra; Willem H. van Riemsdijk (pp. 415-425).
Competitive interaction of carbonate and phosphate on goethite has been studied quantitatively. Both anions are omnipresent in soils, sediments, and other natural systems. The PO4–CO3 interaction has been studied in binary goethite systems containing 0–0.5 M (bi)carbonate, showing the change in the phosphate concentration as a function of pH, goethite concentration, and carbonate loading. In addition, single ion systems have been used to study carbonate adsorption as a function of pH and initial (H)CO3 concentration. The experimental data have been described with the charge distribution (CD) model. The charge distributions of the inner-sphere surface complexes of phosphate and carbonate have been calculated separately using the equilibrium geometries of the surface complexes, which have been optimized with molecular orbital calculations applying density functional theory (MO/DFT). In the CD modeling, we rely for phosphate on recent parameters from the literature. For carbonate, the surface speciation and affinity constants have been found by modeling the competitive effect of CO3 on the phosphate concentration in CO3–PO4 systems. The CO3 constants obtained can also predict the carbonate adsorption in the absence of phosphate very well. A combination of inner- and outer-sphere CO3 complexation is found. The carbonate adsorption is dominated by a bidentate inner-sphere complex,(FeO)2CO. This binuclear bidentate complex can be present in two different geometries that may have a different IR behavior. At a high PO4 and CO3 loading and a high Na+ concentration, the inner-sphere carbonate complex interacts with a Na+ ion, probably in an outer-sphere fashion. The Na+ binding constant obtained is representative of Na–carbonate complexation in solution. Outer-sphere complex formation is found to be unimportant. The binding constant is comparable with the outer-sphere complexation constants of, e.g., SO2−4 and SeO2−4.The molecular geometry of carbonate is used to derive the interfacial charge distribution that is applied to model PO4–CO3 competition experiments.
Keywords: Goethite; Hematite; Ferrihydrite; HFO; Iron oxide; ATR-FTIR; Phosphate; Carbonate; Adsorption; Extended; Stern model; CD model; MUSIC model; Competition; Speciation
Mesoporous silica originating from a gaseous ammonia epoxide ring opening and the thermodynamic data on some divalent cation adsorptions
by José A.A. Sales; Giovanni C. Petrucelli; Fernando J.V.E. Oliveira; Claudio Airoldi (pp. 426-433).
An organofunctionalized mesoporous HMS-like compound has been synthesized by reacting the silylating agent 3-glycidoxypropyltrimethoxysilane with gaseous ammonia. The reaction path leads to the opening of the three membered epoxide ring to incorporate ammonia to give the modified silylating agent. This new silylating agent was used to synthesize a mesostructure inorganic–organic hybrid through the neutral template directing agent, dodecylamine, using a co-condensation process, and exploring the ability of the silicon source tetraethoxysilane. The final solid named HMS-NH has been characterized through elemental analysis, X-ray powder diffraction, nitrogen gas adsorption, infrared spectroscopy and solid state NMR for the29Si nucleus. An amount of1.06±0.10mmol of pendant groups is covalently bonded to the inorganic backbone. The attached basic centers adsorbed divalent cations to give the maxima adsorption capacity of0.74±0.03,0.55±0.06,0.53±0.05 and0.51±0.06mmolg−1 for copper, nickel, zinc and cobalt, respectively. From calorimetric determinations the quantitative thermal effects for all these cation/basic center interactions gave exothermic enthalpy, negative Gibbs free energy and positive entropy. These thermodynamic data confirmed the energetically favorable condition of such interactions at the solid/liquid interface for all systems.
Keywords: Mesoporous silica; Ammonia; Epoxide; Adsorption; Calorimetry; Thermodynamic
Preparation of SiO2@polystyrene@polypyrrole sandwich composites and hollow polypyrrole capsules with movable SiO2 spheres inside
by Tongjie Yao; Quan Lin; Kai Zhang; Dengfeng Zhao; Hui Lv; Junhu Zhang; Bai Yang (pp. 434-438).
In this paper, we describe a flexible method for preparing conducting building blocks: SiO2@polystyrene@polypyrrole sandwich multilayer composites and hollow polypyrrole (PPy) capsules with movable SiO2 spheres inside. First, SiO2@polystyrene (PS) core/shell composites were synthesized, and then SiO2@PS@PPy sandwich multilayer composites were prepared by chemical polymerization of pyrrole monomer on the surface of SiO2@PS composites. Furthermore, hollow polypyrrole capsules with movable SiO2 spheres inside were obtained after removal of the middle PS layer. The diameter of sandwich multilayer composites could easily be controlled by adjusting the dosage of pyrrole monomer. The conductivities of composites increased with the increase of PPy content. After the insulating PS layer was selectively etched, the conductivities of hollow capsules with movable SiO2 spheres inside were much higher than those of the corresponding sandwich multilayer composites.In this paper SiO2@PS@PPy sandwich multilayer composites and hollow PPy capsules with movable SiO2 spheres inside were successfully prepared. Their structures and properties are characterized in detail.
Keywords: Polypyrrole (PPy); Sandwich multilayer composite; SiO; 2; Polystyrene (PS); Building block
Organo-modified ZnAl layered double hydroxide as new catalyst support for the ethylene polymerization
by Fu-An He; Li-Ming Zhang (pp. 439-444).
Organo-modified ZnAl layered double hydroxide was used for the first time to support a nickel a-diimine catalyst for the ethylene polymerization, and its effects on the catalytic activity, the morphology, thermal stability, and dynamic viscoelastic properties of the resultant polyethylene material were investigated. Different from the homogeneous nickel a-diimine catalyst, the supported catalyst system was found to have a long-lasting polymerization activity. Moreover, the resultant polyethylene material showed good particle morphology, improved thermal stability, as well as enhanced storage modulus and complex viscosity.The kinetic curves of the ethylene polymerizations in the presence of the homogeneous nickel a-diimine catalyst and the nickel a-diimine catalyst supported on OZnAl-LDH. Reaction conditions: temperature, 0 °C; Al/Ni molar ratio, 1500.
Keywords: Layered double hydroxide; Nickel; a; -diimine catalyst; Ethylene polymerization; Catalytic activity; Morphology; Thermal stability; Viscoelastic properties
Solubilization of methacrylic acid based polymers by surfactants in acidic solutions
by Nina Vlachy; Didier Touraud; Ksenija Kogej; Werner Kunz (pp. 445-455).
The effect of various surfactants on the solubility of methacrylic acid based polyelectrolytes that are insoluble in water at low pH, i.e. isotactic poly(methacrylic acid), i-PMA, Luviflex® Soft and Luviflex® Silk, was studied by surface tension, fluorescence spectroscopy, potentiometric titration and dynamic light scattering, DLS, measurements. Results show that Luviflex® Silk and Luviflex® Soft form polymeric micelles in aqueous solutions above a well-defined concentration, whereas both i-PMA and Luviflex® Soft undergo a pH-induced conformational transition. The critical association concentration values for each surfactant in the presence of completely ionized polyions were determined. Potentiometric and DLS measurements show that the addition of an anionic and a nonionic surfactant significantly increases the solubility of the polymers at low pH, while the presence of a cationic surfactant results in a formation of an insoluble polymer–surfactant aggregate. The present results could help in regulating the removal of hair-setting polymers by water.Blocks of monomeric units in Luviflex® Silk.
Keywords: Hydrophobic polyelectrolytes; Solubilization; Surfactants; Dynamic light scattering
Simultaneous nanoparticle formation and encapsulation driven by hydrophobic interaction of casein- graft-dextran and β-carotene
by Xiaoyun Pan; Ping Yao; Ming Jiang (pp. 456-463).
Casein- graft-dextran copolymer was produced using the Maillard reaction. The copolymer is molecularly soluble in neutral aqueous solution whereas β-carotene is extremely insoluble. By the method of dialysis or evaporation then dispersing in water, the solubility of hydrophobic complex of casein and β-carotene decreases whereas the solubility of dextran increases gradually, then nanoparticles formed with casein and β-carotene core and dextran shell. The particles have spherical shape and are stable in aqueous solution against dilution, pH change, ionic strength change, FeCl3 oxidation and long time storage. The encapsulated β-carotene can be released by pepsin or trypsin hydrolysis. To our knowledge, this is the first report of simultaneous nanoparticle formation and encapsulation induced by hydrophobic interaction. Casein- graft-dextran copolymer and the nanoparticle preparation is a green process in which only alkali and ethanol, no other chemicals, were used.During evaporation or dialysis process β-carotene interacts with the hydrophobic segments of casein- graft-dextran forming nanoparticle core. Dextran shell makes the nanoparticles stable in water.
Keywords: β; -Carotene; Casein; Copolymer; Dextran; Drug delivery; Nanoparticle
Incorporation of ovalbumin within cationic octadecylamine monolayer and a comparative study with zwitterionic DPPC and anionic stearic acid monolayer
by Tapanendu Kamilya; Prabir Pal; G.B. Talapatra (pp. 464-474).
In this communication we demonstrated the incorporation of water-soluble surface-active protein OVA within an insoluble cationic ODA monolayer and compared with zwitterionic (DPPC) and anionic (SA) monolayer. The incorporation of OVA is found to be more in ODA as compared to that of DPPC and SA. The kinetics of protein adsorption in lipid monolayer gives the idea that unfolding of OVA is less in case of DPPC than SA and ODA. The π– A isotherm and compressibility study gives the information about the different states of the protein–lipid mixed monolayer. At higher pressure, OVA tend to squeeze out from the lipids monolayer. High-resolution field emission scanning electron microscope (FE-SEM) images confirm this observation. The surface morphology of DPPC–OVA LB film is far better than ODA–OVA and SA–OVA LB film. OVA forms large irregular aggregates on SA and ODA monolayer. Fluorescence study reveals that protein structure is perturbed more in SA and ODA system compared to that of DPPC. The overall results indicate that DPPC monolayer is better to get protein lipid mixed film than SA and ODA monolayer.
Keywords: Langmuir–Blodgett film; Ovalbumin; Stearic acid; DPPC; FE-SEM
Adsorption and viscoelastic properties of fractionated mucin (BSM) and bovine serum albumin (BSA) studied with quartz crystal microbalance (QCM-D)
by Adam A. Feiler; Anna Sahlholm; Tomas Sandberg; Karin D. Caldwell (pp. 475-481).
The adsorption profile and viscoelastic properties of bovine submaxillary gland mucin (BSM) and bovine serum albumin (BSA), extracted from a commercial mucin preparation, adsorbing to polystyrene surfaces has been studied using quartz crystal microbalance with dissipation monitoring (QCM-D). A significant difference in the adsorption properties of the different proteins was detected; with the BSA adsorbing in a flat rigid layer whilst the mucin adsorbed in a diffuse, highly viscoelastic layer. Subsequent addition of BSA to the preadsorbed mucin layer resulted in stiffening of the protein layer which was attributed to complexation of the mucin by BSA. In contrast, a preadsorbed layer of BSA prevented mucin adsorption altogether. Combined mixtures of mucin and BSA in well defined ratios revealed intermediate properties between the two separate protein species which varied systematically with the protein ratios. The results shed light on the synergistic effects of complexation of lower molecular weight biomolecular species with mucin. The possibility to selectively control protein uptake and tailor the physical properties of the adsorbed layer makes mucin an attractive option for application in biomaterial coatings.Viscoelastic properties of adsorbed layers mucin and albumin complexes measured using quartz crystal microbalance with dissipation monitoring (QCM-D); potential coating strategy for biomaterials.
Keywords: Bovine submaxillary gland mucin (BSM); Bovine serum albumin (BSA); Quartz crystal microbalance with dissipation monitoring (QCM-D); Protein; Biomaterial; Viscoelastic
Ultrasonic attenuation spectroscopy of emulsions with droplet sizes greater than 10 μm
by Andreas Richter; Tino Voigt; Siegfried Ripperger (pp. 482-492).
Ultrasonic attenuation measurement is a frequently used tool for non-destructive determination of dispersion characteristics. Useful information like particle or droplet size and their concentration can be obtained, if the relation between size and attenuation of the dispersion is known. In this work, the theoretical model by Faran for the intermediate sound wave regime (IWR) is presented in combination with experimental data. In the IWR, the acoustic behavior is governed by elastic scattering rather than by dissipative effects. Experiments with emulsion of droplet sizes greater than 10 μm were carried out. Silicone oil, sunflower oil and olive oil were selected for the disperse phase of the oil-in-water emulsions. First, emulsions having droplets in the micrometer range were created. Afterwords, attenuation measurements of different concentrated emulsion were carried out. Some adjustments reflecting concentration influence were performed to outline the agreement between calculations and measurements. The validity of the model can be confirmed, if the volume fraction of the disperse phase is considered as a variable. Finally, droplet size distributions from theoretical attenuation spectra could be calculated based on a log-normal distribution.
Keywords: Attenuation spectra; Droplet sizes distribution; Emulsions; Scattering; Ultrasonic spectroscopy
Mixed electrolytes producing very weak electroacoustic signal
by Marek Kosmulski; Jarl B. Rosenholm (pp. 493-499).
The electrokinetic potential of powders dispersed in concentrated solutions of salts can be determined by electroacoustic methods when the ESA (electrokinetic sonic amplitude) signal of electrolyte is properly corrected for. We propose an alternative solution to the problem of electroacoustic measurements at high ionic strengths; that is, the composition of mixed electrolytes with common ions can be adjusted to minimize the ESA signal of the electrolyte. The measurement of electrokinetic potential of powders dispersed in such mixed electrolytes does not require electrolyte background correction. Mixed electrolytes, which produce very weak ESA signals, were prepared from the following salts with common ions: Li+ (LiNO3 + LiCl), Na+ (NaNO3 + NaBr), K+ (KBr + KNO3), and NO−3 (LiNO3 + KNO3). Proportions of the components in these mixed electrolytes are concentration dependent. The electrokinetic potentials of alumina in these mixed electrolytes determined with and without background correction were only marginally different.ESA titration of 0.87 m LiNO3
Keywords: Zeta potential; Isoelectric point; Aluminum oxide; Electrokinetic sonic amplitude; Concentrated electrolyte solutions
Uniform particles of pure and silica-coated cholesterol
by Vuk Uskoković; Egon Matijević (pp. 500-511).
Uniform crystalline colloidal cholesterol particles of narrow size distribution were obtained by precipitation. The method consisted of adding a miscible non-solvent (water) into cholesterol solutions of different alcohols and acetone, without any additives. The properties of the resulting particles depended in a sensitive way on the concentration of all reactants, temperature, pH, ionic strength, and aging time. The major observed effects were due to the solubility of cholesterol, which was strongly affected by the solvent mixture and temperature. Precipitation in 1-propanol/water system yielded stable dispersions of well-defined particles, which were used to evaluate the effects of different experimental parameters on their properties. Aging of stable dispersions resulted in multi-layered aggregation of the primary platelets, the degree and rate of which process was strongly affected by temperature. Finally, it was shown that the colloidal cholesterol particles could be coated with homogeneous silica layers in order to alter their surface characteristics.Uniform crystalline colloidal cholesterol particles of narrow size distribution were prepared by precipitation without any additives, and characterized by various techniques.
Keywords: Aggregation of cholesterol; Cholesterol colloidal; Dispersions of cholesterol; Precipitation of cholesterol; Silica-coated cholesterol
Kinetic determination of critical coagulation concentrations for sodium- and calcium-montmorillonite colloids in NaCl and CaCl2 aqueous solutions
by Sandra García-García; Susanna Wold; Mats Jonsson (pp. 512-519).
The stability of the sodium and calcium forms of montmorillonite was studied at different NaCl and CaCl2 concentrations. The aggregation kinetics was determined from the decrease in particle concentration with time at different electrolyte concentrations. The DLVO theory defines the critical coagulation concentration (CCC) value as the electrolyte concentration that balances the attractive and repulsive potential energies between the particles, making aggregation diffusion-controlled. Therefore CCC values were obtained by extrapolation of the aggregation rate constants measured as a function of ionic strength to conditions where the rate constant value is determined by diffusion only. When the electrolyte was CaCl2, the CCC value was found to be approximately two orders of magnitude lower than the CCC values obtained using NaCl as electrolyte.
Keywords: Montmorillonite colloids; CCC; DLVO theory; PCS; Zeta potential; Aggregation
Thermal and colloidal behavior of amine-treated clays: The role of amphiphilic organic cation concentration
by S.I. Marras; A. Tsimpliaraki; I. Zuburtikudis; C. Panayiotou (pp. 520-527).
The modification of sodium montmorillonite (NaMMT) through the insertion of amphiphilic hexadecylammonium cations into the clay's interlayer spaces has been studied. Alkylammonium concentrations equivalent to 0.15–3.00 times the cation exchange capacity of the clay were used. The conformation of the surfactant cations in the confined space of the silicate galleries was investigated by X-ray diffraction analysis and scanning electron microscopy, while the organoclay's thermal stability was examined by thermogravimetric analysis. The clay's surface properties induced by the ion-exchange process were followed by measurements of the mineral's zeta potential as a function of pH and surfactant concentration, while the coagulation rates of organoclay suspensions in water and in chloroform were examined using dynamic light scattering. All the results are consistent with showing that the overall characteristics and thus the behavior of the modified MMT particles strongly depend on the alkylammonium surfactant concentration used in the modification process. This, however, has very important implications for any attempt to incorporate the organomodified MMT particles into different media for various applications such as polymer nanocomposite preparation.Influence of the surfactant concentration (related to the clay CEC) on the coagulation rate of montmorillonite particles dispersed in water.
Keywords: Montmorillonite; Cationic surfactant; Thermal stability; Surface charge; Zeta potential; Coagulation; Dynamic light scattering
Electron transfer studies on cholesterol LB films assembled on thiophenol and 2-naphthalenethiol self-assembled monolayers
by Rakesh K. Pandey; K.A. Suresh; V. Lakshminarayanan (pp. 528-536).
We have formed the cholesterol monolayer and multilayer LB films on the self-assembled monolayers of 2-naphthalenethiol (2-NT) and thiophenol (TP) and studied the electrochemical barrier properties of these composite films using cyclic voltammetry and electrochemical impedance spectroscopy. We have also characterized the cholesterol monolayer film using grazing angle FTIR, scanning tunneling microscopy (STM) and atomic force microscopy (AFM). Cholesterol has a long hydrophobic steroid chain, which makes it a suitable candidate to assemble on the hydrophobic surfaces. We find that the highly hydrophobic surface formed by the self-assembled monolayers (SAM) of 2-NT and TP act as effective platforms for the fabrication of cholesterol monolayer and multilayer films. The STM studies show that the cholesterol monolayer films on 2-NT form striped patterns with a separation of 1.0 nm between them. The area per cholesterol molecule is observed to be 0.64 nm2 with a tilt angle of about 28.96° from the surface normal. The electrochemical studies show a large increase in charge transfer resistance and lowering of interfacial capacitance due to the formation of the LB film of cholesterol. We have compared the behavior of this system with that of cholesterol monolayer and multilayers formed on the self-assembled monolayer of thiophenol.A study of electron transfer and ion permeation properties through the cholesterol Langmuir–Blodgett monolayer and multilayer films formed on 2-napthalenethiol and thiophenol self-assembled monolayers.
Keywords: Cholesterol; Langmuir–Blodgett (LB) film; Self-assembled monolayer; 2-Napthalenethiol; Thiophenol
Composite films of lecithin and heme proteins with electrochemical and electrocatalytic activities
by Yuanbiao Qiao; Fangfang Jian; Huanqing Yu; Lihong Hu (pp. 537-543).
Functional composite films made from lecithin micelles and the two heme proteins of met-myoglobin (Mb) and met-hemoglobin (Hb) are reported in this paper. Proteins in functional composite films have much higher rates of electron transfer than proteins in solutions on carbon paste (CP) electrodes. Cyclic voltammograms (CVs) all give a pair of well-defined and quasi-reversible peaks, corresponding to the heme FeIII/FeII redox couple of proteins. Differential pulse voltammograms (DPVs) also show the same formal potential (E0′) values of proteins under identical conditions. Electronic and vibrational spectra indicate that proteins in these films are not denatured, but their conformational differences from native states may exist. TheE0′ value for Mb in the lecithin film is found to be pH dependent. The Mb lecithin film can catalytically reduce O2 and H2O2, and its analytical application to H2O2 determination is established.Composite films of Hb and Mb in lecithin micelles display direct electron transfer withE0′ values of −0.374 and−0.338V, respectively, in pH 7.0 phosphate buffers.
Keywords: Heme proteins; Lecithin film; Electrochemistry; Electrocatalysis
Effect of magnesium/calcium ratio in solutions subjected to electrodialysis: Characterization of cation-exchange membrane fouling
by Christophe Casademont; Gérald Pourcelly; Laurent Bazinet (pp. 544-554).
Electrodialysis is based on the migration of charged species through perm-selective membranes under an electric field. Fouling, which is the accumulation of undesired solid materials at the interfaces of these membranes, is one of the major problems of this process. The aim of the present work was to investigate the nature and the morphology of fouling observed at different Mg/Ca ratios (R=0, 1/20, 1/10, 1/5, 2/5) on cation-exchange membranes (CEM) during conventional electrodialysis treatments. It appeared that forR=0, the fouling observed on the surface in contact with the basified concentrate was formed of only Ca(OH)2. As soon as magnesium was introduced into the solution treated, CaCO3 was observed. Furthermore, the X-ray diffraction results also identified the CaCO3 observed as calcite. To our knowledge, this is the first time that the presence of magnesium has been demonstrated to induce a CaCO3 fouling on CEM during electrodialysis.The aim of this study was to investigate the effect of magnesium on membrane fouling for different Mg/Ca ratios such asR=0 and 1/10 (ratio observed in milk). It appeared that magnesium would be a catalyst or a germ of growth for CaCO3.
Keywords: Electrodialysis; Cation-exchange membrane; Fouling; Calcium; Magnesium
The synthesis of mesoporous aluminosilicate using microcline for adsorption of mercury(II)
by Xiu-Wen Wu; Hong-Wen Ma; Jin-Hong Li; Jun Zhang; Zhi-Hong Li (pp. 555-561).
An economical mesoporous aluminosilicate was synthesized with microcline as starting material and the precursor 13X zeolite as seed for crystal structure on mesoporous walls. In this method, a mixture of microcline and Na2CO3 with a molar ratio of 1:1.05 was first calcined at 1093 K for 2.5 h. The calcined materials were mixed with 35 ml C16TMABr aqueous solution (containing 8.2 g C16TMABr) and the precursors of 13X zeolite, resulting in mesoporous aluminosilicate after crystallization of the solution at 378 K for 48 h and calcination of the powder at 823 K for 5 h. The as-synthesized sample has a uniform pore diameter distribution centered at 3.7 nm. The as-synthesized sample had BET surface area of 725 m2/g and BJH mean pore diameter of 3.7 nm. The FT-IR results revealed that the building units of 13X zeolite were inserted into the pore walls of the as-synthesized sample. The adsorption ratio of mercury(II) onto the as-synthesized adsorbent was about 95%. The adsorption process was found to be spontaneous and can be explained by particle diffusion and chemical ion-exchange mechanisms. The equilibrium concentration of mercury(II) using the as-synthesized sample as the adsorbent was under 1 μg/L, making the concentration of mercury meet the limit for drinking water in China as recommended by the World Health Organization.Mesoporous adsorbent (surface area: 725 m2/g; mean pore diameter: 3.7 nm) synthesized with microcline. Adsorption to of mercury(II) ions was spontaneous and can be explained with by particles diffusion and chemical ion-exchanged mechanisms.
Keywords: Mesoporous; Microcline; Mercury(II) adsorption; Adsorption mechanism; Aluminosilicate
Cerium modified MCM-41 nanocomposite materials via a nonhydrothermal direct method at room temperature
by Kamal Mohamed Sayed Khalil (pp. 562-568).
Ce-containing MCM-41 materials were prepared via a direct, nonhydrothermal method at room temperature from tetra-ethoxysilane, n-hexadecyl trimethyl ammonium bromide, ammonia solution, and cerium(IV) ammonium nitrate precursors. Composite materials containing the nominated ratios of 5 and 10% (w/w) CeO2/MCM-41 were targeted. The obtained materials were investigated by TGA, DSC, FTIR, diffuse reflectance UV–vis, XRD, N2 adsorption/desorption isotherms, and SEM. Results indicated the insertion of cerium ions in tetrahedral environment in the framework of MCM-41. BET surface area amounting to 824 and 726 m2/g; total pore volume amounting to 0.427 and 0.515 cm3/g; and narrow pore size distribution maximizing at 22.5 and 23.7 Å, respectively were obtained for the 5 and 10% CeO2/MCM-41 calcined composites. SEM showed a spherical type morphology for the composites which is rather similar to their blank MCM-41, and no clear ceria aggregates were observed on the external surfaces of composites spherical particles. Thus, the adopted method allows the persistence of MCM-41 texture with cerium inserts in the framework of MCM-41 and/or forms finely divided ceria nanoparticles on the wall of MCM-41 materials. Moreover, stabilization of any formed ceria nanoparticles was attributed to the short nonintersecting porous nature of MCM-41 matrix, which hinders their aggregation upon calcinations.Ce-containing MCM-41 materials via a direct nonhydrothermal method.
Keywords: MCM-41; Ce-MCM-41; CeO; 2; Mesoporous; Composite material
Coalescence of a bubble at a fluid–fluid interface: Comparison of theory and experiment
by Kai-Bin Fu; John C. Slattery (pp. 569-579).
Coalescence times for air bubbles rising through hexadecane to an air–hexadecane interface are measured and compared with an analysis based upon our previous extension of continuum mechanics to the nanoscale [J.C. Slattery, E.-S. Oh, K. Fu, Chem. Eng. Sci. 59 (2004) 4621–4635] with the assumption of retarded dispersion forces. The relation between the retarded and non-retarded Hamaker constants proposed by Görner and Pich [J. Aerosol Sci. 20 (7) (1989) 735–747] is tested for the first time.As a bubble approaches an interface during the last stage of coalescence, a thin liquid film is formed and deformed as the result of retarded dispersion forces. Its thicknessh∗ is a function of timet∗ and radial positionr∗. The film ruptures and coalescence occurs, whenh∗=0.
Keywords: Coalescence time; Retarded Hamaker constant; Dispersion forces; Van der Waals forces; Nanoscale mechanics
Amphiphilic copolymer grafted “smart surface” enhanced by surface roughness
by Yin Zhu; Minghui Shi; Xuedong Wu; Shengrong Yang (pp. 580-587).
Polystyrene–poly(acrylic acid) (PS–PAA) block copolymers polymerized by atom transfer radical polymerization were covalently grafted to both smooth and microtextured surfaces. These amphiphilic copolymers were utilized to create smart surfaces, which can be responsive to external stimuli, e.g., pH values or organic solvent. Atom force microscopy, field emission scanning electron microscopy, and contact angle measurements were employed to investigate the physiochemical features of the copolymer brushes. It was found that the wettability of surfaces depended on both the PS/PAA molar ratio and external solvent properties. Hydrophilic surfaces were obtained after treatment with basic solution, as well as a polar solvent, such as ethanol. With treatment with acidic solution or toluene, the surface could be reversibly turned relatively hydrophobic, probably due to the rearrangement or reorganization of polymer chains. Moreover, rougher surfaces, which were microtextured by ZnO nanorods, were incorporated into this adaptive system to enhance the tunable range of wettability.We modified surfaces by PS–PAA block copolymer brushes to prepare smart surfaces, the wettability of which can be reversibly switched with external solvents stimulation. Moreover, rougher surface microtextured by ZnO nanorods, was incorporated into this adaptive system to enhance the tunable range of wettability.
Keywords: Amphiphilic copolymer; Smart surface; Reversible surface; Roughness effect
Influence of the Hofmeister series of anions on the molecular organization of positively ionized monolayers of a viologen derivative
by Ignacio Giner; Gorka Pera; Carlos Lafuente; María Carmen López; Pilar Cea (pp. 588-596).
The effects of the Hofmeister series of ions are ubiquitous in chemistry and biology. In this paper specific ion effects on the surface behavior of a viologen dication, namely1,1′-dioctadecyl-4,4′-bipyridilium, are shown. Surface pressure and surface potential vs area isotherms were obtained on aqueous subphases containing potassium salts with several representative counterions in the Hofmeister series (C6H5O3−7, SO2 −4, HPO2−4, Cl−, Br−, NO−3, I−, and ClO−4). The parameters obtained from the compression isotherms (area per molecule, phase transitions, Young modulus, initial surface potential, and variation of the surface potential upon compression) are dependent on the nature of the counterion, indicating ion specificity. Aqueous subphases containing C6H5O3−7, SO2−4, and HPO2−4 anions yield more expanded viologen monolayers and these anions do not effectively penetrate into the monolayer. Brewster angle microscopy was used to map the different phases of the viologen monolayers at the air–water interface. The Langmuir films were also characterized by UV–vis spectroscopy, with quantitative analysis of the reflection spectra supporting an organizational model in which the viologen chromophore undergoes a gradual transition to a more vertical position with respect to the water surface upon compression. A comparison of the tilt angles of the viologen on the different subphases indicates that anions that can more easily penetrate in the monolayer permit the viologen moieties to adopt a slightly more vertical position with respect to the water surface.The influence of the Hofmeister series of anions on the surface behavior of a viologen derivative is analyzed. A different penetration ability of the anions into the positively charged viologen monolayer has been observed, together with a different orientation of the viologen chromophore upon the compression process depending on the subphase nature, revealing the existence of specific ion effects.
Keywords: Hofmeister series; Viologen; Molecular organization; UV–vis reflection spectroscopy; Langmuir films
Thermodynamic quantities of surface formation of aqueous electrolyte solutions
by Norihiro Matubayasi; Ryuji Yoshikawa (pp. 597-600).
To compare the effect of nitrate anions on the surface tension increments of aqueous solutions with that of halide anions, the surface tension of aqueous solutions of lithium nitrate, sodium nitrate, and potassium nitrate was measured as a function of temperature and concentration. It is shown that the surface tension of aqueous alkali metal nitrate solutions is determined primarily by the kinds of anions, since the surface tension increments of these nitrates were of the same magnitude. The importance of the electrical double layer at the surface is discussed in relation to these surface tension increments.
Keywords: Surface tension; Electrolytes
Lyotropic liquid crystalline phases in a ternary system of 1-hexadecyl-3-methylimidazolium chloride/1-decanol/water
by Guodong Zhang; Xiao Chen; Yizhou Xie; Yurong Zhao; Huayu Qiu (pp. 601-606).
Lyotropic liquid crystals formed in a ternary system of 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl), 1-decanol, and water at 25 °C are reported. The hexagonal and lamellar phases were characterized by small angle X-ray scattering and polarizing optical microscopy. In the phase diagram, the system shows two isotropic liquid phases, a hexagonal phase connected to the [C16mim]Cl–water axis, and a lamellar phase in the center. The formation of liquid crystalline phases is believed to arise from a hydrogen-bonded network comprised of an imidazolium ring, anion, 1-decanol, and water. In the liquid crystal, the intercalation of 1-decanol between neighboring [C16mim]Cl molecules favors the appearance of lamellar phases. The phase behavior of the present system is discussed in comparison with a similar ternary system of cetyltrimethylammonium bromide (CTAB).Hexagonal and lamellar lyotropic liquid crystals for 1-hexadecyl-3-methylimidazolium chloride with 1-decanol and water could be formed by H-bond network.
Keywords: Lyotropic liquid crystal; Phase behavior; Phase diagram; Ionic liquid; 1-Hexadecyl-3-methylimidazolium chloride; Cetyltrimethylammonium bromide; Headgroup
Water in oil emulsion droplet size characterization using a pulsed field gradient with diffusion editing (PFG-DE) NMR technique
by Clint P. Aichele; Mark Flaum; Tianmin Jiang; George J. Hirasaki; Walter G. Chapman (pp. 607-619).
This paper describes a proton nuclear magnetic resonance (NMR) technique, pulsed field gradient with diffusion editing (PFG-DE), to quantify drop size distributions of brine/crude oil emulsions. The drop size distributions obtained from this technique were compared to results from the traditional pulsed field gradient (PFG) technique. The PFG-DE technique provides both transverse relaxation (T2) and drop size distributions simultaneously. In addition, the PFG-DE technique does not assume a form of the drop size distribution. An algorithm for the selection of the optimal parameters to use in a PFG-DE measurement is described in this paper. The PFG-DE technique is shown to have the ability to resolve drop size distributions when theT2 distribution of the emulsified brine overlaps either the crude oil or the bulk brineT2 distribution. Finally, the PFG-DE technique is shown to have the ability to resolve a bimodal drop size distribution.An NMR technique is introduced that has the ability to resolve transverse relaxation and drop size distributions simultaneously of unimodal and bimodal water/oil emulsions.
Keywords: Petroleum; Emulsions; NMR; Drop size distribution
Synergistic interactions in the mixed micelles of cationic gemini with zwitterionic surfactants: The pH and spacer effect
by Kulbir Singh; D. Gerrard Marangoni (pp. 620-626).
Mixed micelle formation of binary cationic gemini (12- s-12,s=4, 6) and zwitterionic ( N-dodecyl-N,N-dimethylglycine, EBB) surfactants has been investigated by measuring the surface tension of aqueous solution as a function of total concentration at various pH values from acidic to basic, under conditions of 298.15 K and atmospheric pressure. The results were analyzed by applying regular solution theory (RST), and Motomura's theory, which allows for the calculation of the excess Gibbs energy of micellization purely on the basis of thermodynamic equations. The synergistic interactions of all the investigated cationic gemini + zwitterionic surfactants mixtures were found to be dependent upon the pH of the solution and the length of hydrophobic spacer of gemini surfactant. The evaluated excess Gibbs free energy is negative for all the systems.
Keywords: Surface tension measurements; Mixed micelles; Synergistic interactions; Gemini surfactant; Zwitterionic surfactant
Interfacial properties of heat-treated ovalbumin
by Thomas Croguennec; Anne Renault; Sylvie Beaufils; J. Jean-Jacques Dubois; Stéphane Pezennec (pp. 627-636).
The interfacial properties (kinetics of adsorption at the air/water interface, rheology of the interfacial layer) of ovalbumin molecules, unheated or previously heat-denatured in solution (10 g L−1, pH 7, NaCl 50 mM) under controlled conditions (up to 40 min at 80 °C), were investigated. Heat treatments induced the formation of covalent aggregates which surface exhibits a higher hydrophobicity and an increased exposition of sulfhydryl groups when compared to native ovalbumin (unheated). Although they have a larger hydrodynamic size, aggregates adsorb as fast as native ovalbumin at the air/water interface. However, aggregates are able to established rapid contacts in the interfacial layer as shown by the fast increase of both surface pressure and shear elastic constant. In contrast, native ovalbumin needs longer time to developed intermolecular contacts and exhibits lower foam stability even if the shear elastic constant on aging reached higher value than for ovalbumin aggregates.Compared to native ovalbumin, heat-denatured/aggregated ovalbumin molecules exhibit a more open structure (higher hydrophobicity, exposed free sulfhydryl) favoring rapid contacts at the air/water interface that prevent premature foam destabilization mechanisms.
Keywords: Ovalbumin; Heat-denaturation/aggregation; Adsorption; Surface load; Surface pressure; Interfacial rheology; Foam stability
Improved solubilization of carbamazepine and structural transitions in nonionic microemulsions upon aqueous phase dilution
by Anna Kogan; Abraham Aserin; Nissim Garti (pp. 637-647).
Solubilization capacity and structural transformations in nonionic microemulsions characterized by a large continuous isotropic region forming dilutable self-assembled nanodroplets containing solubilized carbamazepine, were studied along dilution lines 73 and 82 (70 and 80 wt% surfactant and 30 and 20 wt% of oil phase, respectively). The preparations were based on pharma-grade ingredients, water,R-(+)-limonene, ethanol, propylene glycol, and Tween 60. Solubilization capacity (SC) of the drug was dependent on the microstructure of the microemulsion and on the surfactant-to-oil phase weight ratio. The SC in the concentrate (reversed micelles) was 15 times higher than its solubility in the oil. Transition of the W/O microemulsion to a bicontinuous phase and to O/W droplets were indentified by electrical conductivity, viscosity, SAXS, and SD-NMR measurements. Once the system is diluted to 90 wt% aqueous phase, the SC is 10 and 16-fold higher, along dilution lines 73 and 82, respectively, than in pure water. Being solubilized, carbamazepine serves as a cosurfactant therefore it affects the curvatures of the microstructures and consequently the boundaries of the structural regions and the transition points between the different phases. Dilutable microemulsions are promising new carbamazepine vehicles for oral intake.Non-ionic microemulsions are promising nanovehicles for oral carbamazepine intake. Structural transformations upon dilution with aqueous phase of these nanostructures embedded with the drug were studied by electrical conductivity, viscosity, SAXS, and SD-NMR measurements.
The effect of electrolyte on the encapsulation efficiency of vesicles formed by the nonionic surfactant, 2C18E12
by Richard D. Harvey; David J. Barlow; Alex F. Drake; Laila Kudsiova; M. Jayne Lawrence; Anthony P.R. Brain; Richard K. Heenan (pp. 648-661).
Encapsulation efficiencies of vesicles formed by the nonionic surfactant 1,2-dioctadecyl- rac-glycerol-3- ω-methoxydodecylethylene glycol (abbreviated as 2C18E12) and its phospholipid counterpart, distearoylphosphatidylcholine (DSPC) at 298 K, were determined by the entrapment of the water-soluble dye, carboxyfluorescein (CF) to be0.045±0.001 and0.03±0.04 L mol−1 for 2C18E12 vesicles prepared using low osmolarity (270 m Osm) Krebs–Henseleit (K–H) buffer and a modified ‘high salt’ (1600 m Osm) variant of K–H buffer, respectively, and0.64±0.01 and0.31±0.04Lmol−1 for DSPC vesicles prepared under the same conditions and in the same buffers. Freeze fracture electron microscopy studies confirmed the presence of vesicles when 2C18E12 and DSPC were dispersed in water and both buffer solutions. Small angle neutron scattering (SANS) studies, using D2O in place of H2O, showed that when 2C18E12 vesicles were prepared in the ‘high salt’ variant of K–H buffer as opposed to K–H buffer or water, a higher proportion of multilamellar vesicles (MLV) were formed. Furthermore when prepared in the ‘high salt’ variant of K–H buffer, the 2C18E12 bilayers were thinner, and when present in the form of MLV exhibited a smaller layer of water separating the bilayers. However, even in the absence of electrolyte, 2C18E12 formed surprisingly thin bilayers due to the penetration of the polyoxyethylene chains into the hydrophobic chain region of the bilayer. Due to the dehydrating effect of the high concentration of electrolyte present in the ‘high salt’ variant of K–H, the polyoxyethylene head groups penetrated further into the hydrophobic region of the bilayer making the bilayer even thinner. In the case of the DSPC vesicles, although the SANS study showed an increase in the relative proportion of multilamellar to unilamellar vesicles when samples were prepared in the ‘high salt’ variant of K–H buffer, no differences were observed in the thickness and the d-spacing of the vesicle bilayers. Variable temperature turbidity measurements of 2C18E12, and DSPC vesicles prepared in water indicated phase changes at320±0.5 and327±0.5K, respectively, and were unchanged when the ‘high salt’ variant of K–H buffer was used as hydrating medium. Taken together, these results suggest that a low phase transition temperature was not the reason for the poor entrapment efficiency of 2C18E12 vesicles but rather the very ‘thin’ hydrophobic barrier formed by the penetration of the polyoxyethylene chains into the hydrophobic region of the bilayer.An explanation for the anomalously low solute encapsulation by nonionic surfactant vesicles has been obtained through a combination of small angle neutron scattering, electron microscopy, and variable temperature turbidity measurements.
Keywords: Nonionic surfactant vesicles; Small angle neutron scattering; Freeze-fracture electron microscopy; Electrolyte
Friction and adsorption of aqueous polyoxyethylene (Tween) surfactants at hydrophobic surfaces
by Malgorzata Graca; Jeroen H.H. Bongaerts; Jason R. Stokes; Steve Granick (pp. 662-670).
The nanotribological responses of a series of nonionic polyoxyethylene surfactants (Tween 20, Tween 40, Tween 60, and Tween 80) were investigated after they were adsorbed from aqueous solution onto atomically smooth hydrophobic substrates. The hydrophobic surfaces were composed of a condensed monolayer of octadecyltriethoxysilane (OTE; contact angleθ>110°). The nanorheological measurements were performed using a modified surface forces apparatus after coating atomically smooth mica with these OTE monolayers, while adsorption measurements were performed using phase-modulated ellipsometry on silicon wafers coated with these same monolayers. The minimum surface–surface separation observed under high load in friction studies agreed quantitatively with the thickness obtained from ellipsometry. For Tweens 20, 40, and 60, the thickness of the adsorbed film increases with increasing alkyl chain length. Systematic investigations of the nanorheological response showed that there is a “solid-like” elastic response from confined surfactant layers, which is the case for the smallest separations to separations up to slightly larger than twice the adsorbed film thickness. In kinetic friction, these confined layers are characterized by a shear stress of approximately 3 MPa with minimal dependence on shear rate. The magnitude of the sliding shear stress is the same as the apparent yield stress at ≈3 MPa; it is independent of alkyl chain length within the Tween family of surfactants and corresponds to a nominal friction coefficient ofμ∼1. A similar friction coefficient is observed for boundary lubrication on the macroscopic scale in a tribometer utilizing hydrophobic surfaces andμ≈1.1 for Tweens 20, 40, and 60. These results suggest that while Tween molecules adsorb onto hydrophobic surfaces to form a robust separating layer, the lubricating properties of these layers are dominated by a highly dissipative slip plane, the same for all alkyl chain lengths.Surfactant solutions are confined thickness in the SFA. The rheological properties of the films are explored in detail.
Keywords: Tween; Adsorption; Friction; Hydrophobic; SFA; Micelles; Rheology; Tribology; Contact angle; Surfactant; Shear
Adsolubilization of dihydroxybenzenes into CTAB layers on silica particles
by Ling Li; Lushan Wang; Xigang Du; Yao Lu; Zhengyu Yang (pp. 671-677).
The adsolubilization of dihydroxybenzenes (catechol and hydroquinone) into cetyltrimethylammonium bromide (CTAB) layers on silica particles have been investigated by dye method and UV spectrum. It is found that the adsolubilization amount of catechol increases with increasing the concentration of CTAB, reaches a maximum value at the critical micelle concentration (CMC), and then decreases with further increment of CTAB concentration. For hydroquinone, different phenomenon is observed. The maximum adsolubilization amount reaches at critical surface aggregation concentration (CSAC) instead of CMC of the CTAB and then decreases to constant values. In order to analyze the adsolubilization difference between catechol and hydroquinone, we determined the interaction between them and CTAB in the bulk solution by measuring the diffusion coefficient of dihydroxybenzenes with ultramicroelectrode (UME). The individual contributions to the overall apparent diffusion coefficient of dihydroxybenzenes in CTAB solutions were also calculated. The results indicate that more hydroquinone than catechol could interact with CTAB molecules. However, rarely hydroquinone could interact with CTAB micelles compared with catechol. It is suggested that the substitution positions of hydroxyl lead to the difference of the interaction between dihydroxybenzenes and CTAB, which is responsible for the difference of the adsolubilization.The interaction between dihydroxybenzenes and CTAB determined by microelectrode can be used to interpret the adsolubilization mechanism.
Keywords: Ultramicroelectrode; Diffusion coefficient; Interaction; Adsolubilization
Unusual behavior of CMC for binary mixtures of alkyltrimethylammonium bromides: Dependence on chain length difference
by Hideo Akisada; Junko Kuwahara; Ayako Koga; Hideki Motoyama; Hiromitsu Kaneda (pp. 678-684).
The critical micelle concentrations (CMC) of binary mixtures of alkyltrimethylammonium bromides (C nTAB) were measured by a conductivity method. The CMCs of C12TAB-C14TAB and C14TAB-C16TAB systems exhibit the usual behavior, namely a monotonic decrease of the CMC with the mole fraction of the longer chain surfactant. However, the CMC behaviors of C10TAB-C16TAB, C11TAB-C16TAB, C12TAB-C16TAB, and C11TAB-C14TAB are unusual. The behaviors of the CMCs with mole fraction for these systems consist of three regions, of which the first is characterized by a very small decrease of the CMC in the range of low mole fraction, followed by a second where there is an abrupt decrease of the CMC, and a third where the CMCs exhibit their usual behavior. The molecular interaction parameter ω is almost equal to zero for mixtures that have the usual CMC behavior, but is small and positive for those systems with unusual CMCs. We infer that for very low mole fractions of C16TAB, the C16TA ion in the C12TAB-C16TAB system penetrates imperfectly into the micelle and its two methylene groups exist outside the micelle.The CMC for the mixture of dodecyl- and hexadecyltrimethylammonium bromides shows unusal behavior which is a drastic decrease of CMC with remarkable change of micelle composition.
Keywords: Ionic surfactant; Critical micelle concentration; Micelle; Counterion; Binary system; Mixture; Interaction; Composition; Homologous; Conductivity; Regular solution; Alkyltrimethylammonium bromide; Decyltrimethylammonium bromide; Undecyltrimethylammonium bromide; Dodecyltrimethylammonium bromide; Tetradecyltrimethylammonium bromide; Hexadecyltrimethylammonium bromide
Interaction between casein and sodium dodecyl sulfate
by Yan Liu; Rong Guo (pp. 685-692).
The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) with 2.0 mg/ml casein was first investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and fluorescence spectra. ITC results show that individual SDS molecules first bind to casein micelles by the hydrophobic interaction. The micelle-like SDS aggregate is formed on the casein chains when SDS concentration reaches the critical aggregation concentration (c1), which is far below the critical micellar concentration (cmc) of SDS in the absence of casein. With the further increase of SDS concentration to the saturate binding concentrationc2, SDS molecules no longer bind to the casein chains, and free SDS micelles coexist with casein micelles bound with SDS aggregates in the system. DLS results show that the addition of SDS leads to an increase in the hydrodynamic radius of casein micelles with bound surfactant at SDS concentration higher than 4 mM, and also an increase in the casein monomer molecule (or submicelles) at SDS concentration higher than 10 mM. Fluorometric results suggest the addition of SDS leads to some changes in the binding process of hydrophobic probes to casein micelles.The isothermal titration curves for titrating 200 mM SDS into (■) 0; (●) 0.25; (▴) 0.5; (▾) 1.0; (♦) 2.0; (◂) 5.0 mg/mL casein solution.
Keywords: Casein; Sodium dodecyl sulfate; Interaction
Room temperature sphere-to-rod growth and gelation of PEO–PPO–PEO triblock copolymers in aqueous salt solutions
by R. Ganguly; V.K. Aswal; P.A. Hassan (pp. 693-700).
The effects of NaCl and KF on the sphere-to-rod micellar growth behavior of triblock copolymers having two different compositions, (EO)20(PO)70(EO)20 (P123) and (EO)26(PO)40(EO)26 (P85), have been studied by dynamic light scattering (DLS), small angle neutron scattering (SANS) and dilute solution viscometry. NaCl can effectively tune the sphere-to-rod growth temperature of the micelles of both these copolymers and induce micellar growth down to the room temperature and below. The growth behavior is found to be dependent on the composition of the copolymer as P123 being more hydrophobic shows the room temperature growth in the presence of ethanol at significantly lesser NaCl concentration than the less hydrophobic copolymer P85. DLS studies depict for the first time the growth driven transition of the copolymer solutions from dilute to semi-dilute regime as a function of copolymer and salt concentrations. KF can also induce room temperature growth of the P123 micelles at lesser salt concentration than NaCl but it fails to induce any such growth of the P85 micelles. A pseudo-binary temperature-concentration phase diagram on 15% copolymer solutions shows the variation of the sphere-to-rod transition temperature and the cloud point of the copolymer solutions as a function of salt concentration.Room temperature sphere-to-rod growth of PEO–PPO–PEO based copolymer micelles.
Keywords: Triblock copolymer; Micelle; Sphere-to-rod growth; Gel
Aqueous self-assembly of phytantriol in ternary systems: Effect of monoolein, distearoylphosphatidylglycerol and three water-miscible solvents
by Pia Wadsten-Hindrichsen; Johanna Bender; Johan Unga; Sven Engström (pp. 701-713).
The aqueous phase behavior of phytantriol (PT) in mixtures of monoolein (MO), distearoylphosphatidylglycerol (DSPG), propylene glycol (PG), polyethylene glycol 400 (PEG 400) and 2-methyl-2,4-pentanediol (MPD) was investigated by visual inspection, polarized light microscopy and small angle X-ray diffraction at room temperature. The phase diagrams of PT and MO in water are qualitatively very similar and PT/MO mixtures in excess water form one cubic phase of space group Pn3m irrespective of mixing ratio. The addition of the charged membrane lipid DSPG to the PT system gives rise to a considerable water swelling of the cubic phases as well as the occurrence of a cubic phase of space group Im3m. Whereas all three solvents studied give rise to a sponge (L3) phase in the MO–water system, this phase was only found when MPD was added to the PT–water system. The results are discussed with respect to the chemical differences between PT and MO.
Keywords: Cubic phase; Sponge phase; Lamellar phase; Phase behavior; Small angle X-ray diffraction; Phytantriol; Monoolein
SANS studies of the effects of surfactant head group on aggregation properties in water/glycol and pure glycol systems
by Caroline Seguin; Julian Eastoe; Richard K. Heenan; Isabelle Grillo (pp. 714-720).
Aggregation in mixed water–glycol and pure glycol solvents has been investigated with four related surfactants, bearing common C12 tails: anionic, sodium dodecylsulfate (SDS); cationic, dodecyltrimethylammonium bromide (C12TAB); zwitterionic C12-amidopropyldimethylamine betaine (betaine) and nonionic, octaethyleneglycol monododecyl ether (C12E8). The solvent media were water, water/ethylene glycol, and water/propylene glycol mixtures, as well as pure ethylene glycol (EG) and propylene glycol (PG), spanning relative dielectricsεr from 79 to 30. Results from small-angle neutron scattering (SANS) experiments, employing deuterated solvents, were consistent with the presence of ellipsoidal, or cylindrical micelles, depending on solvent and surfactant type. In pure EG and PG solvents the ionic and zwitterionic surfactants exhibit only weak aggregation, with much smaller micelles than normally found in water. However, interestingly, pure EG is identified as a solvent in which nonionic C12E8 aggregates strongly, mirroring the behavior in water. In contrast when the solvent is changed to PG (εr=30) aggregation of C12E8 is only minimal. Hence, aggregation is shown to be strongly dependent on surfactant type and identity of the glycol solvent.SANS curves for 10 wt% surfactant solutions of SDS, C12TAB, betaine, and C12E8 in deuterated ethylene glycol.
Keywords: Micellization; Nonaqueous solvents; Small-angle neutron scattering; Solvophobicity
Diffusioosmotic flows in slit nanochannels
by Shizhi Qian; Biswajit Das; Xiaobing Luo (pp. 721-730).
Diffusioosmotic flows of electrolyte solutions in slit nanochannels with homogeneous surface charges induced by electrolyte concentration gradients in the absence of externally applied pressure gradients and potential differences are investigated theoretically. A continuum mathematical model consisting of the strongly coupled Nernst–Planck equations for the ionic species' concentrations, the Poisson equation for the electric potential in the electrolyte solution, and the Navier–Stokes equations for the flow field is numerically solved simultaneously. The induced diffusioosmotic flow through the nanochannel is computed as functions of the externally imposed concentration gradient, the concentration of the electrolyte solution, and the surface charge density along the walls of the nanochannel. With the externally applied electrolyte concentration gradient, a strongly spatially dependent electric field and pressure gradient are induced within the nanochannel that, in turn, generate a spatially dependent diffusioosmotic flow. The diffusioosmotic flow is opposite to the applied concentration gradient for a relatively low bulk electrolyte concentration. However, the electrolyte solution flows from one end of the nanochannel with a higher electrolyte concentration to the other end with a lower electrolyte concentration when the bulk electrolyte concentration is relatively high. There is an optimal concentration gradient under which the flow rate attains the maximum. The induced flow is enhanced with the increase in the fixed surface charge along the wall of the nanochannel for a relatively low bulk electrolyte concentration.An electric field and a pressure gradient are induced in a slit nanochannel connecting two identical reservoirs on either side which are filled with identical electrolyte solutions with different electrolyte concentrations. The induced electric field and pressure gradient generate diffusioosmotic flow which can be used to manipulate fluids in nanofluidic devices for lab-on-a-chip applications.
Keywords: Diffusioosmosis; Diffusioosmotic flow; Electrokinetics; Electrokinetic flow; Nanofluidics; Electrical double layer (EDL)
Comparison of the Nernst–Planck model and the Poisson–Boltzmann model for electroosmotic flows in microchannels
by H.M. Park; J.S. Lee; T.W. Kim (pp. 731-739).
In the analysis of electroosmotic flows, the internal electric potential is usually modeled by the Poisson–Boltzmann equation. The Poisson–Boltzmann equation is derived from the assumption of thermodynamic equilibrium where the ionic distributions are not affected by fluid flows. Although this is a reasonable assumption for steady electroosmotic flows through straight microchannels, there are some important cases where convective transport of ions has nontrivial effects. In these cases, it is necessary to adopt the Nernst–Planck equation instead of the Poisson–Boltzmann equation to model the internal electric field. In the present work, the predictions of the Nernst–Planck equation are compared with those of the Poisson–Boltzmann equation for electroosmotic flows in various microchannels where the convective transport of ions is not negligible.The electroosmotic flows predicted from the Nernst–Planck model are compared with those from the Poisson–Boltzmann model. The transport of solute particles (a) and the residence time distributions (b) from these two models are also compared.
Keywords: Electroosmotic flow; Poisson–Boltzmann equation; Nernst–Planck equation
Electroosmotic transport through rectangular channels with small zeta potentials
by Debashis Dutta (pp. 740-746).
In this article, we analyze the electroosmotic transport of neutral samples through rectangular channels having a small zeta potential at their walls. Exact analytical expressions have been derived for quantifying the solute velocity in such conduits and the Taylor–Aris dispersivity in large-aspect-ratio rectangular geometries. In addition, a semianalytical theory has been presented for estimating the solutal spreading rate in rectangular profiles of all aspect ratios by decoupling the effects of vertical and horizontal velocity gradients in the system. Finally, the predictions made by this theory have been compared with the results from numerical simulations in which all assumptions were relaxed. Our analysis shows that while the sidewalls in a rectangular conduit modify the fluid velocity only to a moderate extent, they can increase the hydrodynamic dispersion of sample slugs as much as by a factor of 8 under strong Debye-layer overlap conditions. In the opposite limit of thin Debye layers, however, the increase in dispersion due to the side regions is only by a factor of 2 and remains nearly unaffected by the aspect ratio of the channel, in agreement with the prediction by [E.K. Zholkovskij, J.H. Masliyah, J. Czarnecki, Anal. Chem. 75 (2003) 901].Increase in solute dispersion due to the sidewalls of a rectangular conduit under electroosmotic flow conditions. The parameter λ here denotes the ratio of channel depth d to the Debye length.
Keywords: Taylor–Aris dispersion; Electroosmotic flow; Nanofluidic transport; Debye-layer overlap; Rectangular channel
Copper phthalocyanine films deposited by liquid–liquid interface recrystallization technique (LLIRCT)
by K.R. Patil; S.D. Sathaye; R. Hawaldar; B.R. Sathe; A.B. Mandale; A. Mitra (pp. 747-752).
The simple recrystallization process is innovatively used to obtain the nanoparticles of copper phthalocyanine by a simple method. Liquid–liquid interface recrystallization technique (LLIRCT) has been employed successfully to produce small sized copper phthalocyanine nanoparticles with diameter between 3–5 nm. The TEM-SAED studies revealed the formation of 3–5 nm sized with β-phase dominated mixture of α and β copper phthalocyanine nanoparticles. The XRD, SEM, and the UV–vis studies were further carried out to confirm the formation of copper phthalocyanine thin films. The cyclic voltametry (CV) studies conclude that redox reaction is totally reversible one electron transfer process. The process is attributed to Cu(II)/Cu(I) redox reaction.Liquid–liquid interface recrystallization technique (LLIRCT) has been employed successfully to produce small sized copper phthalocyanine nanoparticles with diameter between 3 and 5 nm successfully with perfect reversible behavior.
Keywords: Nanoparticulate films; Copper phthalocyanine; Cyclic voltametry
Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12O40 Langmuir–Blodgett film
by Miao Xu; Yancai Li; Wen Li; Changqing Sun; Lixin Wu (pp. 753-760).
We used the Langmuir–Blodgett (LB) technique to construct a well-defined and structure-controllable photochromic material—a highly ordered multilayer film composed of dioctadecylamine and 12-molybdophosphoric acid (PMo12). We identified well-ordered lamellar structures using X-ray diffraction, polarized IR, and Raman spectra, and we determined a packing model of the two components in the LB film. We found the Keggin structure and fundamental features of the PMo12 ion to be maintained in the hybrid film. This hybrid LB film displayed photochromic properties upon UV light irradiation and we observed the following process from first-order kinetics. The photochromism exhibited the ability to switch between colorless and blue. A fading process occurred when the film was exposed to ambient air or O2 in the dark. During the color change, the packing structure of the film was well maintained. We also examined the electrochemical behavior of the hybrid LB film by cyclic voltammetry in detail and we propose different kinetic mechanisms for the film before and after irradiation.We construct a highly ordered multilayer film composed of dioctadecylamine and 12-molybdophosphoric acid on solid substrate through Langmuir–Blodgett technique. Such a hybrid film displays reversible photochromic property upon UV light irradiation. The electrochemistry of the film proposes different kinetic mechanisms for the film before and after irradiation.
Keywords: Langmuir–Blodgett film; Polyoxometalates; Photochromism; Electrochemistry
Nonideal mixed micelles of Gemini surfactant homologues and their application as templates for mesoporous material MCM-48
by Jun Hu; Lihui Zhou; Jian Feng; Honglai Liu; Ying Hu (pp. 761-767).
The micellization properties of aqueous solutions of the mixed Gemini surfactant homologues GEM16-6-16 and GEM16-12-16 with various compositions were investigated. The measured critical micelle concentration (CMC) deviated significantly from the ideal mixing model. Good agreement was found with a nonideal mixing model, the Margules model, which has two optimal parameters,A12=−3.611 andA21=−6.318. It was shown that the properties of mixed micelles were not sensitive to the compositions, and most of the GEM16-12-16 molecules were aggregated into the micelles. Dynamic laser light-scattering measurements revealed that the mixed micelles had almost the same size and similar zeta potential. When the mixed micelles were used as templates, a series of highly ordered cubic MCM-48 mesoporous materials, characterized by XRD and TEM, were produced through self-assembly. The N2 adsorption–desorption measurements suggested that the pores of these materials had similar average diameters of 2.2–2.5 nm. This further demonstrated the nonideal behavior of the homologue mixture.Gemini surfactant homologues GEM16-6-16 and GEM16-12-16 are nonideal mixed micelles and have template approaches for ordered mesoporous materials MCM-48.
Keywords: Gemini surfactant homologues; Mixed micelles; Pseudo-phase separation model; Template; MCM-48
Inverse gas chromatography as a tool for investigation of nanomaterials
by Kalina Batko; Adam Voelkel (pp. 768-771).
Inverse gas chromatography (IGC) is presented as a representative tool for the investigation of nanomaterials: Aerosil200V and two iron oxides (nanohematite and nanogoethite). IGC was used for characterization of the surface properties of materials. Parameters describing their surface properties are calculated from the retention data of test solutes injected into a column filled with the solid of interest. It is possible to determine the surface activity and the Hamaker constants of different nanomaterials.Hamaker constant may be determined by inverse gas chromatography. It is shown that the use of constant value of Hamaker parameter in simulation procedures in disperse system cannot be advised.
Keywords: Inverse gas chromatography; Nanoparticles; Hamaker constant
On the modified Tabor parameter for the JKR–DMT transition in the presence of a liquid meniscus
by Dewei Xu; Kenneth M. Liechti; K. Ravi-Chandar (pp. 772-785).
The JKR, DMT, Maugis models and Tabor parameter for contact under normal loading have been developed based mainly on solid–solid (van der Waals) interactions. In this case, the characteristic length scale for the adhesive forces in the Tabor parameter is the equilibrium interatomic spacing. However, for contact in humid environments, where a liquid meniscus may be present, capillary forces with a longer force range related to the Kelvin radius dominate. Fogden and White [J. Colloid Interface Sci. 138 (1990) 414] introduced a parameter that includes the Kelvin radius for the JKR–DMT transition. This topic was also addressed by Maugis and Gauthier-Manuel [J. Adhes. Sci. Technol. 8 (1994) 1311] who included capillary effects within the frame work that Maugis had previously established. The parameters introduced by Fogden and White and Maugis and Gauthier-Manuel can be viewed as a modified Tabor parameter for the JKR–DMT transition. In the present work, the Kelvin equation linking the Kelvin radius and the relative humidity was explicitly included in the modified Tabor parameter. This provided a quantitative description of the JKR–DMT transition in terms of the relative humidity. This parameter was examined via load and contact radius measurements, where the latter were obtained from Bowden and Tabor's assumption that the friction forcef=τA. The friction experiments were conducted at two different humidity levels using a newly-developed mesoscale friction tester (MFT), which provides a very wide range of contact radii. The modified Tabor parameter was used to reexamine data from pull-off experiments in water and cyclohexane vapor environments [L.R. Fisher, J.N. Israelachvili, Colloids Surf. 3 (1981) 303 and H.K. Christenson, J. Colloid Interface Sci. 121 (1988) 170]. Finally, guidelines are presented for the appropriate choice of contact mechanics models to be used in interpreting data from SFA and AFM experiments in humid environments.
Keywords: Contact mechanics; Liquid meniscus; Surface energy; JKR; DMT; Kelvin radius
Adhesion maps of spheres corrected for strength limit
by Haimin Yao; Michele Ciavarella; Huajian Gao (pp. 786-790).
Present understanding of adhesion is mostly due to the well-known contact theories for spheres, including JKR (Johnson–Kendall–Roberts), DMT (Derjaguin–Muller–Toporov) and MD (Maugis–Dugdale). Since most of the models exhibit their optimal applicability only in a specific regime, an adhesion map has been developed [K.L. Johnson, J.A. Greenwood, J. Colloid Interface Sci. (1997)] to guide the selection among different models. In the JG (Johnson–Greenwood) map, however, an important physical fact has been neglected that the adhesion strength must not exceed the theoretical strength; thereby the applicability of the classical adhesion models is overestimated and misguidance may arise from the JG map. To avoid this limitation, in this paper we introduce the strength limit into the adhesion map and find that the selection of adhesion models depends not only on the Tabor number but also on the ratio of the theoretical strength to the stiffness. Given this ratio, there exists a critical Tabor number or the size of the sphere, below which adhesion is dominated by the limiting strength and the classical adhesion models are no longer appropriate for spheres. These results eventually lead to a corrected adhesion map for spheres.This paper aims to advance the theory of adhesive contact mechanics, in particular the well-known Johnson–Greenwood adhesion map, into the regime governed by the theoretical strength of adhesive forces.
Keywords: Contact mechanics; Surface energy; Adhesion
A simple method for the preparation of activated carbon fibers coated with graphite nanofibers
by Byung-Joo Kim; Soo-Jin Park (pp. 791-794).
A simple method is described for the preparation of activated carbon fibers (ACFs) coated with graphite nanofibers (GNFs). Low-pressure-plasma mixed-gas (Ar/O2) treatment of the ACFs led to the growth of GNFs on their surface. The growth was greater at higher power inputs, and from TEM observations the GNFs were seen to be of herringbone type. It was found that the N2 adsorption capacity of the ACFs did not sharply decrease, and that volume resistivity of the ACFs enhanced as a result of this treatment.
Keywords: Graphite nanofibers; Activated carbon fibers; Plasma treatments; Electric resistivity
Wet-chemical approach to three-dimensional gold nanocorallines: Synthesis and application in surface-enhanced Raman spectroscopy
by Shaojun Guo; Erkang Wang (pp. 795-799).
The shape-controlled synthesis of micrometer-sized gold nanocoralline was simply realized via a wet-chemical approach. The as-prepared hierarchical gold nanocorallines (HGNs) on the solid substrate were initially applied in SERS analysis with 4-aminothiophenol (4-ATP) as the probe molecule. The HGN-modified glass substrate exhibits a higher SERS effect (one order of magnitude higher) than the aggregated gold nanoparticle (∼25 nm)-modified glass substrate.The shape-controlled synthesis of micrometer-sized gold nanocoralline was simply realized via a wet-chemical approach. The as-prepared hierarchical gold nanocorallines (HGNs) on the solid substrate were initially applied in SERS analysis with 4-aminothiophenol (4-ATP) as the probe molecule. The HGN-modified glass substrate exhibits a higher SERS effect (one order of magnitude higher) than the aggregated gold nanoparticle (∼25 nm)-modified glass substrate.
Keywords: Nanomaterial; SERS; Gold nanocoralline; Biosensor; Hierarchical structure
Supramolecular interactions between β-cyclodextrin and hydrophobically end-capped poly(ethylene glycol)s: A quartz crystal microbalance study
by Khémara Kham; Mohamed Guerrouache; Benjamin Carbonnier; Mathieu Lazerges; Hubert Perrot; Marie-Claude Millot (pp. 800-804).
In this study, the supramolecular interactions occurring between β-cyclodextrin-based surfaces and macromolecular chains modified at one end with naphthyl, adamantyl, or phenyladamantyl hydrophobic groups were investigated by means of a quartz crystal microbalance. β-Cyclodextrin-functionalized gold electrodes were obtained through the amide-coupling reaction between mono-6-deoxy-6-amino- β-cyclodextrin and 11-mercaptoundecanoic acid self-assembled monolayer allowing the reproducible preparation of densely grafted surfaces with host properties. The interaction data obtained for the three different modified poly(ethylene glycol)s are in good agreement with our previous studies performed by high performance liquid chromatography and surface plasmon resonance. This evidences that the driving force for the supramolecular interaction is based on the inclusion of the hydrophobic terminal group of the chains within the cyclodextrin cavities. The reversibility of the inclusion process was proven through the regeneration of the original host properties of the sensing surfaces using sodium dodecylsulfate as a competitor for the desorption of the poly(ethylene glycol) chains. β-Cyclodextrin-functionalized surface was prepared and supramolecular interaction investigation with hydrophobic methoxypoly(ethylene glycol) was performed by the quartz crystal microbalance showing that the driving force for interaction is based on inclusion complexes.
Keywords: Quartz crystal microbalance; β; -Cyclodextrin; Poly(ethyleneglycol); Inclusion complexe; Surface regeneration
Interactions between hairy rod anionic conjugated polyelectrolytes and nonionic alkyloxyethylene surfactants in aqueous solution: Observations from cloud point behaviour
by Sofia M. Fonseca; M. Ermelinda Eusébio; Ricardo Castro; Hugh D. Burrows; Maria José Tapia; Ulf Olsson (pp. 805-809).
The effect of three anionic, hairy-rod fluorene based conjugated polyelectrolytes on the cloud points of the alkyloxyethylene surfactants C10E3, C12E4, C12E5, and C12E6 has been studied in aqueous solution. Although the association behaviour of these rigid polymers with surfactants is different from that of more flexible polyelectrolytes, both types of polymers are seen to increase the cloud points, probably as a consequence of associative interactions. The possible importance of Coulombic interactions is suggested by the decrease in cloud points with these systems in the presence of NaCl. With the conjugated polyelectrolytes, the effect appears to be most pronounced with poly[9,9-bis(4-phenoxybutylsulfonate)fluorene- co-2,5-thienylene], which may result from specific interactions between oxyethylene groups and the thiophene ring. The value of cloud point behaviour in designing water based formulations for preparation of devices of these conjugated polyelectrolytes is discussed.Conjugated polyelectrolytes with rigid backbones interact with alkyloxyethylene surfactants in water through similar associative interactions to more flexible ones, leading to increases in solubility and cloud points.
Keywords: Conjugated polyelectrolytes; Nonionic surfactants; Cloud points
The photophysical determination of the minimum hydrotrope concentration of aromatic hydrotropes
by Miguel G. Neumann; Carla C. Schmitt; Katia R. Prieto; Beatriz E. Goi (pp. 810-813).
A method based on the aggregate to monomol emission ratio,Iaggr/Imonomol, was used to determine the minimal hydrotropic concentration (MHC) of aromatic hydrotropes. The main advantage of this method is that it does not require the use of probes or other additives, which might disrupt the aggregation process. Also, it relies on spectrophotometric measurements, which are more sensitive and less arduous than others, like conductivity, light scattering and surface tension.
Keywords: Hydrotropes; MHC; Minimal hydrotropic concentration
Refractive index of sparse layers of adsorbed gold nanoparticles
by Miao Chen; Roger G. Horn (pp. 814-817).
Measurements are presented of the effective complex refractive index of a layer of gold nanoparticles adsorbed to a silicon wafer at low coverages. The measurements were made by means of variable-angle ellipsometry, and correlated with nanoparticle coverage determined from atomic force microscope images. The analysis establishes the effective refractive index of a uniform layer whose thickness equals the nanoparticle diameter. A simple empirical relationship is obtained for real component of refractive index as a function of the fractional nanoparticle coverage regardless of the nanoparticle size. The imaginary component also follows a simple relationship but only up to a certain coverage, above which it increases rapidly. These relationships may be useful in other contexts such as chemical or biosensors in which the nanoparticle coverage could be inferred from optical measurements such as ellipsometry, surface plasmon resonance spectroscopy, reflectometry, or interferometry.The effective refractive index of a layer of gold nanoparticles is measured at low coverages, and shown to be a simple function of volume fraction.
Keywords: Refractive index; Gold nanoparticles; Thin films; Optical properties
by Arthur Hubbard (pp. 818-818).