Journal of Colloid And Interface Science (v.304, #1)

Adsorption and desorption behavior of Bovine Serum Albumin (BSA) on surface-modified magnetic nanoparticles covered with thermosensitive polymer (PNIPAM) was investigated as a function of temperature, pH, and ionic strength. Functionalization of surface-modified magnetic particles was performed by seed polymerization using N-isopropylacrylamide (PNIPAM) as the main monomer. Characterization of these particles was carried out using transmission electron micrography (TEM), and vibrating sample magnetometry (VSM). The adsorption results exhibited both pH and temperature sensitivity. The results showed that the temperature effect on adsorption/desorption behavior was mainly dependent on the properties of the particles' surface. The effect of pH was also investigated and it was observed that a smaller amount of protein was adsorbed at higher pH because of the electrostatic repulsive force between protein molecules and latex particles. The maximum amount of protein was adsorbed near the isoelectric point of BSA. Desorption results showed that more protein was desorbed when adsorption was done at lower temperatures and desorption efficiency was found to be higher than 80%.
Keywords: Thermosensitive magnetic particles; N-isopropylacrylamide; Adsorption; Desorption; Isoelectric point; Bovine Serum Albumin;

A viscose-rayon-based activated carbon cloth (ACC) was electrochemically oxidized to enhance its cation sorption capacity for comparison with as-received ACC. The ACCs were characterized by sodium capacity measurement, pH titration, zeta potential measurement, elemental analysis, Brunauer–Emmet–Teller surface area, and pore size distribution. Batch sorption experiments showed that electrochemically oxidized ACC (EO) is more effective for the removal of lead and copper ions compared to unoxidized ACC (UO) for both competitive and noncompetitive sorption. For electrochemically oxidized fibers the copper and lead sorption capacities of ACC increased 17 and 4 times, respectively, for noncompetitive sorption and 8.8 and 8.6 times, respectively, for competitive sorption. However, reduction in the sorption capacities for both metals was observed for the competitive sorption. The sorption of lead and copper onto EO was by ion exchange, while that onto UO was likely to be due to surface complex formation. The affinity order of the two metal ions sorbed by UO and EO is Pb 2 + > Cu 2 + . The effect of pH on sorption isotherms indicated that metal uptake increased with an increase in solution pH.A viscose-rayon-based activated carbon cloth (ACC) was electrochemically oxidized to enhance its copper and lead sorption capacity. The detailed ACC characterization and sorption studies have been reported.
Keywords: Viscose-rayon-based activated carbon cloth; Lead; Copper; Sorption isotherms; Electrochemical oxidation; Competitive and noncompetitive sorption; Characterization;

Study of the selection mechanism of heavy metal (Pb2+, Cu2+, Ni2+, and Cd2+) adsorption on clinoptilolite by Myroslav Sprynskyy; Bogusław Buszewski; Artur P. Terzyk; Jacek Namieśnik (21-28).
The study was carried out on the sorption of heavy metals (Ni2+, Cu2+, Pb2+, and Cd2+) under static conditions from single- and multicomponent aqueous solutions by raw and pretreated clinoptilolite. The sorption has an ion-exchange nature and consists of three stages, i.e., the adsorption on the surface of microcrystals, the inversion stage, and the moderate adsorption in the interior of the microcrystal. The finer clinoptilolite fractions sorb higher amounts of the metals due to relative enriching by the zeolite proper and higher cleavage. The slight difference between adsorption capacity of the clinoptilolite toward lead, copper, and cadmium from single- and multicomponent solutions may testify to individual sorption centers of the zeolite for each metal. The decrease of nickel adsorption from multicomponent solutions is probably caused by the propinquity of its sorption forms to the other metals and by competition. The maximum sorption capacity toward Cd2+ is determined as 4.22 mg/g at an initial concentration of 80 mg/L and toward Pb2+, Cu2+, and Ni2+ as 27.7, 25.76, and 13.03 mg/g at 800 mg/L. The sorption results fit well to the Langmuir and the Freundlich models. The second one is better for adsorption modeling at high metal concentrations.
Keywords: Clinoptilolite; Sorption; Ion exchange; Heavy metals;

Study of cetyltrimethylammonium and cetylpyridinium adsorption on montmorillonite by Petr Praus; Martina Turicová; Soňa Študentová; Michal Ritz (29-36).
Adsorption of cetyltrimethylammonium (CTA) and cetylpyridinium (CP) onto Na-rich montmorillonite (MMT) was studied. For this purpose, the adsorption isotherms of CTA and CP, along with desorption curves of metal cations (Na+, K+, Ca2+, Mg2+), were obtained by means of capillary isotachophoresis and atomic absorption spectrometry. Infrared, X-ray diffraction pattern, specific surface area, porosity, and moisture adsorption measurements of montmorillonite revealed that CTA and CP were adsorbed in monolayer arrangements. CTA is assumed to be attached to the negatively charged MMT surface mainly by electrostatic forces. On the other hand, CP, adsorbed in higher amounts, can be additionally bound via other interactions of pyridinium rings, such as induced and π – π interactions. By the surfactant adsorption, the montmorillonite surface became hydrophobic and its micro- and mesopores were significantly diminished. Using scanning electron microscopy, aggregation of such organically modified MMT particles was observed.
Keywords: Adsorption; Intercalation; Montmorillonite; Cationic surfactants; Cetyltrimethylammonium; Cetylpyridinium;

Solvent effect on the aggregate of fluorinated gemini surfactant at silica surface by Xiaoyan Song; Peixun Li; Yilin Wang; Chuchuan Dong; Robert K. Thomas (37-44).
The aggregate states of partially fluorinated gemini surfactant [(CF3)2CF(CF2)2(CH2)10N(CH3)2]2(CH2)6Br2 (CF 5C10–C6–C10CF 5) on silica surface were investigated with atomic force microscopy (AFM) and water contact angle (CA) measurement by analyzing the effects of bulk concentration and adsorption time on stack state. On surfactant-adsorbed silica surfaces, there was a flat surface layer interspersed with some scattering surfactant aggregates. In the case of short adsorption times, the aggregates would be hemisphere. In the case of long adsorption times, the aggregates would be present in the form of bilayers. With the increase of bulk concentration, the adsorbed amount was enlarged and the surface layer became more compact. The formation of patchy bilayer aggregates indicated the saturation of the surface layer. Furthermore, organic solvent effects on the aggregate state of the surfactant on a silica surface were studied with four organic solvents, including n-hexane, dehydrated ethanol, 1,1,2-trichloro-1,2,2-trifluoroethane, and toluene. With the treatment of different organic solvents, the hemisphere aggregates on the surface layer can rearrange into spherical bilayer, rodlike monolayer, and branched rodlike monolayer aggregates, respectively. The polarity of solvents and affinity of organic solvents for surfactant molecules may have a great impact on the stack state of the fluorinated gemini surfactant molecules.
Keywords: Fluorinated gemini surfactant; Surfactant adsorption; Silica surface; Organic solvent effect;

Layer-by-layer assembly of intact polydiacetylene vesicles with retained chromic properties by Anupat Potisatityuenyong; Gamolwan Tumcharern; Stephan T. Dubas; Mongkol Sukwattanasinitt (45-51).
Photopolymerized vesicles of 10,12-pentacosadiynoic acid (PPCDA) were successfully assembled into polyelectrolyte multilayer (PEM) thin films using either chitosan or poly(ethylenimine) (PEI) as a polycation. The PEM films assembled from chitosan or PEI polycation retained the blue color of PPCDA vesicles. For the blue films, an increase in absorbance at 635 nm as a function of the number of deposited layers of PPCDA vesicles was observed, confirming the uniform layer-by-layer deposition process. The spherical structures of PPCDA vesicles, as well as their important colorimetric responses to solvent (ethanol), pH, and temperature, are retained in the PEM film. Compared to the vesicles dispersed in water, the PEM films are much more stable to aging. Layer-by-layer assembly thus provides a convenient means to prepare colorimetric sensing devices, with extended shelf life, from polydiacetylene vesicles.
Keywords: Adsorption; Colorimetry; Multilayer film; Polydiacetylene; Sensor; Vesicle;

Adsorption of a hazardous dye, erythrosine, over hen feathers by Vinod K. Gupta; Alok Mittal; Lisha Kurup; Jyoti Mittal (52-57).
Erythrosine is a popular dye that is widely used in cosmetics, foodstuffs, medicines, and textiles. It is highly toxic to mankind and can lead to many diseases including carcinogenicity. Removal of erythrosine has been carried out using waste material—hen feathers—as adsorbent. The effects of pH, concentration of the dye, temperature, and adsorbent dosage have been studied. Adsorption of erythrosine over hen feathers has been correlated with Freundlich and Langmuir isotherms and satisfies both models. The adsorption process has been found endothermic in nature and thermodynamic parameters, Gibb's free energy ( Δ G 0 ), change in enthalpy ( Δ H 0 ), and change in entropy ( Δ S 0 ) have been calculated. The paper also includes results on the kinetic measurements of adsorption of the dye on hen feathers at different temperatures. The adsorption follows a first-order kinetics at all the temperatures and values of the rate constant ( k ad ) have been calculated as 0.0179, 0.0177, and 0.0172 s−1 at 30, 40, and 50 °C, respectively. By rate expression and treatment of data it has been ascertained that the adsorption of erythrosine over hen feathers follows a particle diffusion mechanism.
Keywords: Erythrosine; Hazardous dye; Low-cost adsorbents; Adsorption;

Atomic force microscopy (AFM) measurements were employed to assess polymer–surface interfacial interaction strength. The main feature of the measurement is the use of contact-mode AFM as a tool to scratch off the polymer monolayer adsorbed on the solid surface. Tapping-mode AFM was used to determine the depth of the scraped recess. Independent determination of the layer thickness obtained from optical phase interference microscopy (OPIM) confirmed the depth of the AFM scratch. The force required for the complete removal of the polymer layer with no apparent damage to the substrate surface was determined. Polypropylene (PP), low-density polyethylene (PE), and PP-grafted-maleic anhydride (PP-g-ma) were scraped off silane-treated glass slabs, and the strength of surface interaction of the polymer layer was determined. In all cases it was determined that the magnitude of surface interaction force is of the order of van der Waals (VDW) interactions. The interaction strength is influenced either by polymer ability to wet the surface (hydrophobic or hydrophilic interactions) or by hydrogen bonding between the polymer and the surface treatment.A method was developed for the assessment of the strength of interaction between a polymer melt and a solid surface using contact-mode AFM “scratch” measurements.
Keywords: AFM; Contact mode; Adhesion; Surface treatment; Composite; Polymer adsorption;

The membrane binding and model lipid raft interaction of synthetic peptides derived from the caveolin scaffolding domain (CSD) of the protein caveolin-1 have been investigated. CSD peptides bind preferentially to liquid-disordered domains in model lipid bilayers composed of cholesterol and an equimolar ratio of dioleoylphosphatidylcholine (DOPC) and brain sphingomyelin. Three caveolin-1 peptides were studied: the scaffolding domain (residues 83–101), a water-insoluble construct containing residues 89–101, and a water-soluble construct containing residues 89–101. Confocal and fluorescence microscopy investigation shows that the caveolin-1 peptides bind to the more fluid cholesterol-poor phase. The binding of the water-soluble peptide to lipid bilayers was measured using fluorescence correlation spectroscopy (FCS). We measured molar partition coefficients of 104 M−1 between the soluble peptide and phase-separated lipid bilayers and 103 M−1 between the soluble peptide and bilayers with a single liquid phase. Partial phase diagrams for our phase-separating lipid mixture with added caveolin-1 peptides were measured using fluorescence microscopy. The water-soluble peptide did not change the phase morphology or the miscibility transition in giant unilamellar vesicles (GUVs); however, the water-insoluble and full-length CSD peptides lowered the liquid–liquid melting temperature.
Keywords: Lipid rafts; Fluorescence microscopy; Fluorescence correlation spectroscopy; Cholesterol; Bilayers; Lipid domains; Membranes;

To investigate globular protein–protein and protein–salt interactions in electrolyte solutions, a potential of mean force including hard-core repulsion, van der Waals attraction and electric double layer repulsion is proposed in this work. Both van der Waals attraction and double-layer repulsion are represented using hard spheres with two-Yukawa tails. The explicit analytical solution of osmotic pressure is derived from the first-order mean spherical approximation. From the comparison between the calculated and experimental values of osmotic pressures for aqueous bovine serum albumin (BSA), lysozyme, α-chymotrypsin, and immuno-gamma-globulins (IgG) solutions, we found that the proposed model is adequate for the description of the interactions between proteins at low ionic strength and small self-association of protein molecules. At high ionic strength, the charge inversions of protein molecules should be taken into account.The hard-core two-Yukawa model is able to accurately describe the osmotic pressure of aqueous globular protein solutions as functions of protein concentration, pH, and ionic strength in the case of no self-association.
Keywords: Osmotic pressure; Globular proteins; Yukawa potential; Bovine serum albumin; Lysozyme; α-Chymotrypsin; IgG; Equation of state;

Highly dispersed TiO2 nanoparticles were successfully synthesized by a wet impregnation method using SBA-15 as hard template for confining the growth of TiO2 nanocrystals, and then calcined at 550 °C in muffle furnace for 2 h. The as-synthesized samples were characterized with Fourier transform infrared spectra (FTIR), Raman spectroscopy, diffuse reflectance UV–visible spectroscopy (UV–vis), powder X-ray diffraction (XRD), small-angle X-ray diffraction (SAXRD), nitrogen adsorption, transmission electron microscopy (TEM) and photoluminescence spectra (PL). It was found that SBA-15 contained abundant silanol groups after removal of triblock copolymers by ethanol extraction and could easily adsorb a great number of titanium alkoxide via chemisorption. After subsequent hydrolysis of the anchored Ti complexes and calcination of the amorphous TiO2, anatase TiO2 nanocrystals with spherical shape and uniform particle diameter of about 6 nm were formed. A blue shift was observed in UV–vis absorption spectra due to the quantum size effect of TiO2 nanoparticles. Moreover, the as-prepared TiO2 nanoparticles showed a high PL intensity due to an increase in the recombination rate of photogenerated electrons and holes under UV light irradiation.
Keywords: Mesoporous silica; SBA-15; Ethanol extraction; TiO2; Nanoparticles;

In this study, we attempt to present a direct synthesis of narrowly dispersed silver nanoparticles in a highly concentrated organic phase ( > 2   M ) without the use of a size-selection process. The fully organic phase system contains silver nitrate as a silver precursor, n-butylamine as a medium dissolving the silver salt, dodecanoic acid as a capping molecule, toluene as a medium, and NaBH4 as a reducing reagent. Even using only generic chemicals, monodisperse silver nanocrystals with a size of 7 nm were easily synthesized on the 100-g scale in a 1-L reactor. In addition, systematic studies revealed that the silver nanocrystals synthesized through in situ ligand exchange were stabilized through bidentate bridging of carboxyl groups in dodecanoic acid.
Keywords: Silver; Nano; Ligand; Complex;

Inertial turbulent and acoustic orthokinetic particle coagulation mechanisms have physical similarity. We consider analytically and numerically coagulation of discrete compact and fractal submicron agglomerated particles, governed by these mechanisms via Smoluchowski equation. Existence of the inertial turbulent coagulation is mathematically proven. A new gelation scenario is revealed for both of the above coagulation mechanisms. Turbulent inertial gelation is manifested by means of a multi-modal relay-type run-away particle size growth, including formation of infinite set of secondary maxima in volume fraction distribution. When acoustic coagulation mechanism is much stronger than the Brownian coagulation, acoustic coagulation occurs as a quasi-gelation process, with a run-away particle size growth, characterized, however, by a finite set of secondary maxima. The effect of acoustic field on coagulation is shown to be more pronounced for fractal agglomerates than that for compact agglomerated particles.Discrete Smoluchowski equations are investigated for physically similar inertial turbulent and acoustic orthokinetic coagulation of submicron particles. A new scenario of development of gelation is revealed. Turbulent inertial gelation proceeds in the form of a multi-modal relay-type run-away particle size growth including formation of infinite set of secondary maxima in volume fraction distribution. In the case of acoustic quasi-gelation there also exists a run-away particle size growth, characterized, however, by a finite set of secondary maxima points with decay of maximum volumes of the secondary peaks.
Keywords: Coagulation; Gelation; Aerosol; Fractal agglomerates; Acoustics;

Turbidity measurement for the absolute coagulation rate constants of suspensions has been extensively adopted because of its simplicity and easy implementation. A key factor in deriving the rate constant from experimental data is how to theoretically evaluate the so-called optical factor involved in calculating the extinction cross section of doublets formed during aggregation. In a previous paper, we have shown that compared with other theoretical approaches, the T-matrix method provides a robust solution to this problem and is effective in extending the applicability range of the turbidity methodology, as well as increasing measurement accuracy. This paper will provide a more comprehensive discussion of the physical insight for using the T-matrix method in turbidity measurement and associated technical details. In particular, the importance of ensuring the correct value for the refractive indices for colloidal particles and the surrounding medium used in the calculation is addressed, because the indices generally vary with the wavelength of the incident light. The comparison of calculated results with experiments shows that the T-matrix method can correctly calculate optical factors even for large particles, whereas other existing theories cannot. In addition, the data of the optical factor calculated by the T-matrix method for a range of particle radii and incident light wavelengths are listed.The calculation of optical factors in turbidity measurement and associated technical details using the T-matrix method are presented and shown to be superior to other existing theories.
Keywords: Coagulation; Turbidity measurement; Absolute coagulation rate constant; Optical factor; T-matrix method;

Effect of floc structure on the rate of Brownian coagulation by Tomonori Fukasawa; Yasuhisa Adachi (115-118).
A modified expression for the Smoluchowski solution for the temporal evolution of the number concentration of flocs subject to Brownian coagulation is proposed, taking into account the effect of the growth of floc structure. In the proposed equation, the effect is expressed as a decrease of free volume in the liquid phase due to the increase of effective floc volume in accordance with the progress of coagulation. The validity of the proposed equation was tested by coagulation experiments using polystyrene latex particles. Direct counting of the number of flocs under microscopy provided accurate data on the temporal evolution of the number concentration of flocs. The obtained rate gradually increases in accordance with the growth of floc structure. This behavior agreed exactly with the prediction based on the proposed equation.A modified expression for the Smoluchowski solution for the temporal evolution of the number concentration of flocs subject to Brownian coagulation is proposed, taking into account the effect of the decrease of free volume in the liquid phase due to the increase of effective floc volume in accordance with the progress of coagulation.
Keywords: Coagulation rate; Brownian coagulation; Floc structure; Excluded volume effect; Polystyrene sulfate latex;

Surface properties of submicrometer silica spheres modified with aminopropyltriethoxysilane and phenyltriethoxysilane by Zhijian Wu; Hong Xiang; Taehoon Kim; Myung-Suk Chun; Kangtaek Lee (119-124).
The surface of submicrometer silica spheres are modified with aminopropyl and phenyl groups through a one-step process. Various experimental techniques, i.e., scanning electron microscopy (SEM), quasi-elastic light scattering (QELS), differential scanning calorimetry (DSC), thermogravimetry (TG), zeta potential measurement, nitrogen sorption, and water vapor and organic dye adsorption are used to comprehensively characterize the pure (TEOS particles) and modified silica particles. The SEM micrographs of the particles demonstrate that the modified particles are spherical with uniform size and shape. The particles modified with aminopropyl groups (APTES particles) show the highest isoelectric point (IEP) and the highest weight loss at 780 °C because of the basic nature of aminopropyl groups and the higher reactivity of aminopropyltriethoxysilane. The particles modified with the phenyl groups (PhTES particles) show the lowest water vapor adsorption because their surface is more hydrophobic than that of TEOS and APTES particles. The organic dye (brilliant blue FCF or BBF) adsorption experiments demonstrate that the adsorption capacity of the particles increases greatly after acidification. This is caused by the protonation of silanol groups and amine groups on the particle surface, which presents an enhanced electrostatic attraction with BBF anions. The APTES particles exhibit the highest dye adsorption due to the hydrophobic attractions and the enhanced electrostatic attractions from aminopropyl groups.The surface of submicrometer silica spheres are modified with aminopropyl and phenyl groups through a one-step process and various experimental techniques are used to comprehensively characterize the particles.
Keywords: Surface modification; Silica spheres; Aminopropyltriethoxysilane; Phenyltriethoxysilane; Surface properties; Organic dye adsorption;

Diffuse reflectance infrared Fourier transform spectroscopy as a tool to characterise water in adsorption/confinement situations by Thierry Richard; Lionel Mercury; François Poulet; Louis d'Hendecourt (125-136).
We present experimental data acquired by diffuse reflectance infrared spectroscopy in the mid-IR (4000–400 cm−1), on micrometric-sized mineral grain powders. The spectral evolution of the OH-stretching band is followed when the adsorbed water film is thinned under dry conditions, from high to low hydration states. The IR bands are found to be characteristic of the degree of adsorption/confinement of the liquid water. The OH-stretching band is shifted toward shorter wavenumbers than in bulk water, showing that a significant portion of adsorbed water has a higher intermolecular bonding energy. Complementary treatment of the kinetics of water desorption, varying with the surface forces in the water film, confirms the relationships of these bands with the constrained water state. We distinguish different water types obeying liquid–liquid interactions (free and capillary water) or dominated by solid–water interactions (confined and adsorbed water). Part of this study is devoted to mesoporous silica MCM-41, of interest due to the restricted geometries of its mesopores (4.7 nm) favouring the confined water state. The methodology allows us to distinguish bulk and adsorbed/confined water, using spectral analysis coupled with an understanding of the dynamic behaviour of the desorption process.Infra-red absorbance of water wetting-filling MCM-41 powder under increasingly drying conditions with time. After raw data reduction, the variation of the OH-stretching vibration with the solid–liquid interactions is highlighted.
Keywords: IR spectroscopy; Diffuse reflectance; Adsorbed water; Confinement; Desorption rate;

Iron incorporated heterogeneous catalyst from rice husk ash by Farook Adam; Kalaivani Kandasamy; Saraswathy Balakrishnan (137-143).
Silica supported iron catalyst was prepared from rice husk ash (RHA) via the sol–gel technique using an aqueous solution of iron(III) salt in 3.0 M HNO3. The sample was dried at 110 °C and labeled as RHA-Fe. A sample of RHA-Fe was calcined at 700 °C for 5 h and labeled as RHA-Fe700. X-ray diffraction spectrogram showed that both RHA-Fe and RHA-Fe700 were amorphous. The SEM/EDX results showed that the metal was present as agglomerates and the Fe ions were not homogeneously distributed in RHA-Fe but RHA-Fe700 was shown to be homogeneous. The specific surface areas for RHA-Fe and RHA-Fe700 were determined by BET nitrogen adsorption studies and found to be 87.4 and 55.8 m2 g−1, respectively. Both catalysts showed high activity in the reaction between toluene and benzyl chloride. The mono-substituted benzyltoluene was the major product and both catalysts yielded more than 92% of the product. The GC showed that both the ortho- and para-substituted monoisomers were present in about equal quantities. The minor products consisting of 16 di-substituted isomers were also observed in the GC–MS spectra of both catalytic products. The catalyst was found to be reusable without loss of activity and with no leaching of the metal.The catalyst, RHA-Fe and RHA-Fe700 was prepared from rice husk ash silica. It was used in the benzylation of toluene as shown in the figure. The mono-substituted product was found to be the major yield with more 92%. The mono-substituted product was found to be a mixture of ortho- and para-isomers. These isomers were successfully separated in the GC and the distribution of these isomers was found to be in a 1:1 ratio.
Keywords: Rice husk ash; Heterogeneous catalyst; Iron supported catalyst; Sol–gel; Friedel–Craft benzylation;

Mg0/Pd4+ was able to dechlorinate > 99 % of extractable DDT (initial concentration of 10 mg DDT kg−1 of soil) and > 90 % of extractable DDT (initial concentration of 50 mg DDT kg−1 of soil) in soil slurry. Mg0/Pd4+ was also found to be effective in dechlorinating of 50 mg kg−1 DDD and DDE, in soil aged for varying time periods. GC-MS analyses revealed the formation of 1,1-diphenylethane as an end product from DDT, DDE and DDD. To the best of our knowledge this is the first report describing the application Mg0/Pd4+ system for remediation of DDT, DDD and DDE contaminated soil. We conclude that reductive dechlorination reaction catalyzed by Mg0/Pd4+ may be a promising system to remediate soil contaminated with DDT and its dechlorinated products such as DDD and DDE.DDT is dechlorinated to the hydrocarbon end product, diphenylethane (DPE) in soil by Mg0/Pd4+ bimetallic system using acetone-biosurfactant as the solubilizing phase. Molecular hydrogen generated through corrosion of Mg0 is dissociatively absorbed onto reducing catalyst, palladium (doped on the surface of magnesium) to produce the nascent hydrogen, which in turn dechlorinates the target compound.
Keywords: DDT; DDE; DDD; Dechlorination; Diphenylethane; Magnesium; Palladium;

The adsorption and reaction in supercritical CO2 of the titanate coupling reagent NDZ-201 on the surfaces of seven metal oxide particles, SiO2, Al2O3, ZrO2, TiO2 (anatase), TiO2 (rutile), Fe2O3, and Fe3O4, was investigated. FTIR and TG analysis indicated that the adsorption and reaction were different on different particle surfaces. On SiO2 and Al2O3 particles, there was a chemical reaction of the titanate coupling reagent on the surfaces. On the surfaces of ZrO2 and TiO2 (anatase) particles, there were two kinds of adsorption, weak and strong adsorption. On the surfaces of TiO2 (rutile), Fe2O3, and Fe3O4 particles, there was only weak adsorption. The acidity or basicity of the OH groups on the particle surface was the key factor that determined if a surface reaction occurred. When the OH groups were acidic, the titanate coupling reagent reacted with these, but otherwise, there was no reaction. The surface density of OH groups on the original particles and the amount of titanate coupling reagent adsorbed and reacted were estimated from TG analysis. The reactivity of the surface OH groups of Al2O3 particles was higher than that of the SiO2 particles.The reaction and adsorption of the titanate coupling reagent depend on the acid–base property of the OH groups on the particle surface.
Keywords: Supercritical fluid; Titanate coupling reagent; Reaction; Acid–base property; OH groups;

Polymer-microsphere-stabilized gold metallic colloids have been prepared by a novel strategy of simple and convenient reduction of the metallic salt through the stabilization of the active carboxylic acid group on the gel and surface layer of the microsphere. The nature of the interaction between the carboxylic acid and Au nanoparticles was studied in detail by XPS. Preliminary results indicate that polymer-microsphere-stabilized gold colloids are active catalysts for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride as reductant. The catalytic properties of the stabilized catalyst for recycling were also investigated.Polymer-microspheres-stabilized gold metallic colloids were prepared as a catalyst for the reduction of 4-nitrophenol to 4-aminophenol by reduction of the metallic salt through the stabilization of the carboxylic acid group on the microsphere.
Keywords: Polymer microsphere; Carboxylic acid; Gold; Metallic colloids; Catalytic reduction;

Enhancement of titanium dioxide photocatalysis by water-soluble fullerenes by Vijay Krishna; Naoki Noguchi; Ben Koopman; Brij Moudgil (166-171).
Fullerenes are known for their unique electronic properties including high electron affinity. Although use of fullerenes for scavenging photo-generated electrons from titanium dioxide particles has been demonstrated, no attempts have been made to utilize the unique properties of fullerenes to increase the efficacy of photocatalysis. The present study has demonstrated that a mixture of water-soluble polyhydroxy fullerenes (PHF) and titanium dioxide (anatase polymorph) enhances photocatalytic degradation of organic dye. The PHF molecules adsorbed to the surface of titanium dioxide due to electrostatic forces, with adsorption density being higher at lower pH values. The surface coverage of titanium dioxide nanoparticles by PHF molecules determined the extent of enhancement, with an optimum dosed weight ratio of PHF to titanium dioxide at 0.001. Hydroxylation and concomitant solubilization of fullerenes allow their unique electronic properties to be harnessed for photocatalysis.The photocatalytic enhancement observed on addition of C 60 ( OH ) n depends on their surface coverage of TiO2 nanoparticles and the proposed mechanism of enhancement is photo-generated electron scavenging by C 60 ( OH ) n .
Keywords: Photocatalysis; Titanium dioxide; Water-soluble fullerenes;

The adsorption of binary mixtures of cetyltrimethylammonium bromide (CTAB) and cetyldimethylbenzylammonium chloride (CDBACl) at the mercury/electrolyte interface was studied in various electrolyte systems. The optimum surfactant concentration and electrolyte ratio was searched for, to obtain the formation of a condensed film at as wide a potential range as possible at the highest temperature possible. The optimum conditions found were 2 × 10 −4   M CTAB and 2 × 10 −4   M CDBACl in 0.07 M KF and 0.03 M KBr at 2 °C. The capacitances vs time curves were used for the reconstruction of isochronous capacitance vs potential curves. These curves showed that in that system the condensed film was formed in the potential range from −0.4 to −1.9 V vs Ag/AgCl in less than 220 s. The stability of this film, following the removal of the mercury drop from the solution, was also studied.The curves show that in the selected system at 2 °C the condensed film is formed in a wide potential range from −0.4 to −1.9 V vs Ag/AgCl, in less than 220 s.
Keywords: Cetyltrimethylammonium bromide; Cetyldimethylbenzylammonium chloride; Condensed film; Differential capacitance;

Modelling the shrinkage in pigmented coatings during drying: A stick–slip mechanism by G.M. Laudone; G.P. Matthews; P.A.C. Gane (180-190).
Pigmented coatings, used to improve optical and printing properties, are applied to fibrous paper substrates as slurry, which then dries. We have elucidated the mechanism of the shrinkage which occurs during drying. The void space of the dry coating layers and their effective solid skeletal elements were modelled using the porous network simulation software Pore-Cor. The water-filled porous structures at the beginning of the shrinking process were modelled by creating simulated structures with the same effective skeletal element size distribution as the dry ones, but with higher given porosity to account for the water present. The capillary forces acting on the surface of the drying coating were calculated for the model structures and found to be orders of magnitude larger than the experimentally measured shrinkage forces. The shrinkage process was therefore postulated as resulting from the effect of capillary forces resisted by a discrete stick–slip process. The differences in the visco-elastic properties of the slurries also supported this postulate, as did further experimental evidence.Drying process of a pigmented coating layer using mercury porosimetry, rheology, and the Pore-Cor model.
Keywords: Shrinkage; Paper coating; Stick–slip; Drying; Pore network; Network modelling; Skeletal elements; Calcium carbonate;

A concentration polarization model for the ultrafiltration of nonionic surfactants by A.-S. Jönsson; B. Jönsson; H. Byhlin (191-199).
A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration. The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data.Mass transport during ultrafiltration of nonionic surfactants.
Keywords: Ultrafiltration; Nonionic surfactant; Concentration polarization;

The surface phase behavior of di-n-dodecyl hydrogen phosphate (DDP) in Langmuir monolayer and its interactions with l-arginine (l-arg) have been investigated by measuring π – A isotherms with a film balance and observing monolayer morphology with a Brewster angle microscopy (BAM). The DDP monolayers on pure water show a first-order liquid expanded–liquid condensed (LE–LC) phase transition and form fingering LC domains having uniform brightness at different temperatures. At 15 °C, the π – A isotherms on pure water and on different concentration solutions of l-arg show a limiting molecular area at ∼ 0.50 nm 2 / molecule . With increasing the subphase concentration of l-arg up to 4.0 × 10 −4 M , the LE and the LE–LC coexistence regions shift to larger molecular areas and higher surface pressures, respectively. With a further increase in the concentration of l-arg beyond this critical concentration, these isotherms show little or no more expansion. These results have been explained by considering the fact that the l-arg undergoes complexation with the DDP to form l-arg–DDP that remains in equilibrium with the components at the air–water interface. As the concentration of l-arg in the subphase increases, the equilibrium shifts towards the complex. At a concentration of l-arg ⩾ 4.0 × 10 −4 M , the DDP monolayers get saturated and show the characteristics of the new amphiphile, l-arg–DDP. BAM is applied to confirm the above results. When the concentration of the l-arg is < 4.0 × 10 −4 M , domains always start forming at an area of ∼ 0.64 nm 2 / molecule , which is the critical molecular area for the phase transition in the DDP monolayers on pure water. In contrast, when the monolayers are formed on a solution containing ⩾ 4.0 × 10 −4 M l-arg, comparatively smaller size domains are formed after the appearance of a new cusp point at ∼ 0.55 nm 2 / molecule . With an increase in the concentration of l-arg in the subphase, the size of the domains decreases indicating that the fraction of the DDP gradually decreases, whereas the fraction of the complex gradually increases. In addition, a very simple procedure for determination of the stability constant, which is 2.6 × 10 4 M −1 at 15 °C, has been suggested.Expansion of π – A isotherms of the DDP monolayers in the presence of l-arg at 15 °C.
Keywords: Langmuir monolayers; Phase transition; Di-n-dodecyl hydrogen phosphate; l-arginine; Brewster angle microscopy; Stability constant;

The dynamics of thin liquid films on surfaces whose wettability changes in a time-periodic manner are examined in this work. A nonlinear evolution equation based on the lubrication approximation is used to describe the film height, and attractions due to van der Waals forces are incorporated. Film wettability is varied through an imposed sinusoidal modulation of the Hamaker constant. A linear stability analysis predicts that if the mean Hamaker constant is negative, disturbances at the film surface will eventually decay regardless of the amplitude and frequency of the oscillation. However, numerical solution of the evolution equation shows that the film can rupture at a given frequency if the amplitude is sufficiently large. The associated characteristic wavelength can be predicted from results for constant-wettability surfaces if an appropriate effective Hamaker constant is used. For positive mean Hamaker constants, film rupture can be accelerated, delayed, or prevented depending on how the Hamaker constant changes early in the oscillation cycle. The effects of spatial gradients in wettability are also considered, and it is found that oscillation can delay but not prevent rupture. Inclusion of short-range repulsive forces leads to the formation of droplet-like structures separated by ultra-thin films, but this can be prevented by sufficiently large and slow oscillations of the Hamaker constant. The results of this work may find use in applications that make use of surfaces whose wettability can be controlled by external stimuli.
Keywords: Thin liquid films; Wettability; Time-periodic; Stability; Hamaker constant;

Detergency in spontaneously formed emulsions by Vibhor K. Srivastava; Gautam Kini; Deeleep Rout (214-221).
We report a microemulsion system with commercial nonionic surfactants, which produces kinetically stable o/w emulsions with sub-micron sized oil droplets, when added to water/brine. These emulsions have shown to be promising for fabric detergency. It is hypothesized that superior detergency could be due to (i) a low value of oil–emulsion interfacial tension (0.01–7 mN/m) even at a low ( ⩽ 1   g / l ) surfactant concentration, thus effecting rapid emulsification and solubilisation of oily matrix/film present in dirt and (ii) extremely tiny emulsion oil droplets (50–100 nm), which can have easy access to dirt entrapped in the inter-yarn voids. The aim of this work was to investigate the above factors in a model system (cellulose-coated glass slides with attached oil droplets) with a view to detergency. Further, an attempt was made to study changes in contact angles of oil droplets attached to cellulose-coated glass slides immersed in the emulsion system as a function of brine concentration. Correlations were drawn between equilibrium contact angle, interfacial tension and detergency at different brine concentrations through arguments of work of adhesion and showed an excellent match with detergency trends on commercial fabric test monitors. These correlations also provide insights into possible underlying mechanisms that account for detergency at each level of brine concentrations. An important consequence of the work is that superior detergency is achieved when the oil, present in the microemulsion, is physico-chemically similar to those oils which are to be removed from contaminated surfaces.Contact angle changes for light liquid paraffin oil (LLPO) and caprylic acid blend (19:1 weight ratio) on cellulose coated glass plate, immersed in an emulsion. The oil–water interfacial tension is 0.02 mN/m.
Keywords: Microemulsion; Oil–water interfacial tension; Phase inversion; Nanoemulsion; Cellulose film; Contact angle; Detergency;

Exact knowledge of the dead time as part of the bubble lifetime in the maximum bubble pressure method is an important prerequisite for accurate dynamic surface tension measurements. The duration of the dead time depends essentially on the capillary geometry and affects significantly the measured surface tensions of concentrated surfactant solutions. Increase of the dead time leads to a significant surface tension decrease of a freshly formed bubble surface due to the significantly higher residual adsorption of the surfactant molecules. It is shown that correct dynamic surface tensions are obtained with the experimental procedure of Sugden's method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant.Correct dynamic surface tensions can be obtained with the two-capillary bubble pressure method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant.
Keywords: Dynamic surface tension; Maximum bubble pressure method; Surfactant solutions; Adsorption kinetics; Analysis of effective adsorption time;

The polar surface fluid model is used to derive the generalized dynamic shape equation and the interfacial rheological material functions for viscoelastic membranes and curved interfaces, taking viscous bending and torsion modes into full account. The materials modeling approach based on the polar surface fluid leads to the integration of bending and torsion dissipative modes with their elastic counterparts that appear in the dynamic shape equation and in the interfacial rheological functions. The covariant bending and torsion rates derived in this paper are shown to be related to the interfacial co-rotational derivative of the curvature tensor. The dynamic shape equation is used to analyze shape fluctuation in planar geometries, and to establish the role of bending dissipation in shape dynamics. The dynamic shape equation generalizes the static Helfrich shape equation by incorporating bending and torsion dissipation, and it generalizes the dynamic shape equation based on the Boussinesq–Scriven model by incorporating bending and torsion elasticity and dissipation.
Keywords: Interfacial rheological model; Dynamic shape equation; Torsion and bending viscosities; Thermal fluctuations;

Integral equation for calculation of distribution function of activation energy of shear viscosity by V.M. Gun'ko; E.V. Goncharuk; O.V. Nechypor; S.V. Pakhovchishin; V.V. Turov (239-245).
A new technique of calculation of a distribution function of activation energy ( f ( E ) ) of shear viscosity based on a regularization procedure applied to the Fredholm integral equation of the first kind has been developed using the Baxter-Drayton and Brady model for concentrated and flocculated suspensions. This technique has been applied to the rheological data obtained at different shear rates for aqueous suspensions with fumed silica A-300 and low-molecular (3,4,5-trihydroxybenzoic acid and 1,5-dioxynaphthalene) or high-molecular (poly(vinyl pyrrolidone) of 12.7 kDa and ossein of 20–29 kDa) compounds over a wide concentration range (up to 25 wt% of both components) and at different temperatures. Monomodal f ( E ) distributions are observed for the suspensions with individual A-300 or A-300 with a low amount of adsorbed organics. In the case of larger amounts of nanosilica and organics the f ( E ) distributions are multimodal because of stronger structurization and coagulation of the systems that require a high energy to break the coagulation structures resisting to the shear flow.A new technique of calculation of a distribution function of activation energy of shear viscosity is developed using the Baxter-Drayton and Brady model for concentrated and flocculated suspensions.
Keywords: Viscosity; Shear rate; Activation energy distribution; Fumed silica; 3,4,5-Trihydroxybenzoic acid; 1,5-Dioxynaphthalene; Poly(vinyl pyrrolidone); Ossein; Aqueous suspension;

The electrokinetic pumping characteristics of nanoscale charged porous media packed in microchannels are investigated using a mesoscopic evolution method. When the pore size of porous media is comparable to the thickness of electric double layer, the effects of particle surface potentials on the bulk electric potential distribution will not be negligible. The lattice Poisson–Boltzmann method provides an accurate numerical solution for such problems, which combines two sets of lattice evolution methods solving the nonlinear Poisson–Boltzmann equation for electric potential distribution and the Navier–Stokes equations for fluid flow, respectively. The effects of the finite particle size, the bulk ionic concentration, the external electric field strength and the surface potentials on the electroosmotic micropump performances are therefore studied. The results show that for a certain porosity the maximum pumping pressure is inversely proportional to the particle diameter and the flow rate under zero pressure drop increases with the particle size. The pumping flow rate decreases with the backpressure yet increases with the external electric field strength, linearly respectively. The averaged flow rate increases with the bulk ionic concentration and the particle surface potential, but is slightly influenced by the surface potentials of channel walls. The numerical results agree with the published experimental data while some results deviate from the predictions based on the macroscopic linear assumptions.We perform a full numerical modeling of the electroosmotic flow in charged nanoscale porous media packed in microchannels and analyze the improved performances of the electrokinetic micropump.
Keywords: Electrokinetic effect; Micropump; Lattice Poisson–Boltzmann method; Porous media;

We investigate the interaction between a nanoparticle and an oil–water interface with particular emphasis on the particle crossing through the interface. The formation of a three-phase contact line is investigated in two cases, namely in the presence and in the absence of surface forces. We carefully examine the interplay between capillary and surface forces in such systems. Two instabilities of the interface (snap-in/snap-out) as the particle is moved through the interface are identified and quantitatively described. While the snap-in instability was observed in some AFM studies, the precise interface position and configuration relative to the particle at the instability depends on the nature of the surface forces present in the system. After the snap-in, the particle is adsorbed and must overcome an energy barrier due to the interface deformation in order to cross-over to the other liquid. We make quantitative predictions on the interface configuration at the instabilities and the free energy barrier height. The roles of particle size and different interaction parameters characterizing the system in determining the magnitude of the energy barrier for crossing and in the formation of a three-phase contact line are discussed. Ultimately, this study will enable us to make quantitative predictions on capillary effects in nanoparticle-microemulsions mixtures and other colloidal systems. For particles in the micrometer range and larger the capillary forces dominate over the surface forces and dictate how the snap-in occurs. However, the situation becomes different for particle sizes smaller than about 100 nm. The presence of surface forces modifies the interface configuration and the free energy jump at the snap-in instability.Surface forces play an important role in the way a solid nanoparticle adsorbs to and deforms a liquid interface. We predict the position of the snap-in and snap-out instabilities as well as the free energy profiles as a result of the inerplay between capillary and surface forces.
Keywords: Nanoparticle adsorption; Oil–water interface; Particle–interface interaction; Capillary forces; Contact angle; Surface forces; Free energy profile; Interface instability;

Versatile transmission ellipsometry to study linear ferrofluid magneto-optics by E.S. Kooij; A.C. Gâlcă; B. Poelsema (261-270).
Linear birefringence and dichroism of magnetite ferrofluids are studied simultaneously using spectroscopic ellipsometry in transmission mode. It is shown that this versatile technique enables highly accurate characterisation of magneto-optical phenomena. Magnetic field-dependent linear birefringence and dichroism as well as the spectral dependence are shown to be in line with previous results. Despite the qualitative agreement with established models for magneto-optical phenomena, these fail to provide an accurate, quantitative description of our experimental results using the bulk dielectric function of magnetite. We discuss the results in relation to these models, and indicate how the modified dielectric function of the magnetite nanoparticles can be obtained.Spectroscopic ellipsometry in transmission mode is used to simultaneously measure the magnetic field dependence of linear birefringence and dichroism.
Keywords: Spectroscopic ellipsometry; Magneto-optics; Magnetite nanoparticles; Ferrofluids;

Investigating sorption-driven dissolved organic matter fractionation by multidimensional fluorescence spectroscopy and PARAFAC by Michael R. Banaitis; Heidi Waldrip-Dail; Melinda S. Diehl; Brett C. Holmes; James F. Hunt; Ryan P. Lynch; Tsutomu Ohno (271-276).
Soil organic matter is involved in many ecosystem processes, such as nutrient supply, metal solubilization, and carbon sequestration. This study examined the ability of multidimensional fluorescence spectroscopy and parallel factor analysis (PARAFAC) to provide detailed chemical information on the preferential sorption of higher-molecular-weight components of natural organic matter onto mineral surfaces. Dissolved organic matter (DOM) from soil organic horizons and tree leaf tissues was obtained using water extracts. The suite of fluorescence spectra was modeled with PARAFAC and it was revealed that the DOM extracts contained five fluorescing components: tryptophan-like (peak location at excitation <255 nm:emission 342 nm), tyrosine-like (276 nm:312 nm), and three humic-substance-like components (<255 nm:456 nm, 309 nm:426 nm, <255 nm:401 nm). In general, adsorption onto goethite and gibbsite increased with increasing DOM molecular weight and humification. PARAFAC analysis of the pre- and post-sorption DOM indicated that the ordering of sorption extent was humic-like components (average 91% sorption) > tryptophan-like components (52% sorption) > tyrosine-like components (29% sorption). This differential sorption of the modeled DOM components in both the soil organic horizon and leaf tissue extracts led to the fractionation of DOM. The results of this study demonstrate that multidimensional fluorescence spectroscopy combined with PARAFAC can quantitatively describe the chemical fractionation process due to the interaction of DOM with mineral surfaces.
Keywords: Organic matter; Fluorescence spectroscopy; Parallel factor analysis; Goethite; Gibbsite;

Surface modification of hydroxyapatite nanocrystals by grafting polymers containing phosphonic acid groups by Hyung Woo Choi; Hong Jae Lee; Kyung Ja Kim; Hyun-Min Kim; Sang Cheon Lee (277-281).
A novel approach for the surface modification of hydroxyapatite (HAp) nanocrystals is described by grafting polymerization of vinyl phosphonic acid (VPA) using a redox initiating system in an aqueous media. Fourier transform infrared (FT-IR) and XRD analyses confirmed the modification reaction on HAp surfaces. Inductively coupled plasma mass spectroscopy (ICP MS) showed that the Ca/P molar ratio decreased from 1.67 to 1.36 with increasing the feed VPA amount. Zeta potentials of unmodified HAp and modified HAp in phosphate-buffered saline (PBS) solutions (pH 7.4, ionic strength = 10 mM) were negative and decreased with increasing the amount of grafted PVPA. Transmission electron microscopy (TEM) measurements and time-dependent phase monitoring indicated that the colloidal stability of modified HAp over unmodified HAp in water dramatically increased and tended to exist as single nanocrystals without aggregation.
Keywords: Hydroxyapatite; Phosphonic acid; Surface modification; Grafting; Colloidal stability;