Journal of Colloid And Interface Science (v.284, #1)

Dendrimer modified magnetite nanoparticles for protein immobilization by Bi-feng Pan; Feng Gao; Hong-chen Gu (1-6).
A cascading polyamidoamine (PAMAM) dendrimer was synthesized on the surface of magnetite nanoparticles to allow enhanced immobilization of bovine serum albumin (BSA). Characterization of the synthesis revealed exponential doubling of the surface amine from generations one through four starting with an amino silane initiator. Furthermore, transmission electron microscopy (TEM) revealed clear dispersion of the dendrimer-modified magnetite nanoparticles in methanol solution. The dendrimer-modified magnetite nanoparticles were used to carry out magnetic immobilization of BSA. BSA immobilizing efficiency increased with increasing generation from one to five and BSA binding amount of magnetite nanoparticles modified with G5 dendrimer was 7.7 times as much as that of magnetite nanoparticles modified with only aminosilane. There are two major factors that improve the BSA binding capacity of dendrimer-modified magnetite nanoparticles: one is that the increased surface amine can be conjugated to BSA by a chemical bond through glutaraldehyde; the other is that the available area has increased due to the repulsion of surface positive charge.
Keywords: Polyamidoamine (PAMAM) dendrimer; Protein immobilization; Magnetite nanoparticle; Bovine serum albumin (BSA);

Dynamic Monte Carlo (DMC) simulations of the adsorption of simple protein-like chains are used to more clearly define the molecular basis for the dependence of adsorption thermodynamics on the stability of the unique lowest-energy “native state” conformation of the chain. Arai and Norde were among the first to show that proteins of low native-state stability strongly denature upon adsorption to weakly attractive sorbent surfaces, while relatively modest changes in conformation are observed in stable proteins under identical adsorption conditions. When the protein has a low native-state stability, favorable adsorption entropies are typically observed in such systems, leading to the general belief that the chain gains conformational entropy during adsorption through a net reduction in intramolecular interactions specific to the native-state structure. Analysis of energy landscapes generated from our DMC simulation results show that a net loss in specific intramolecular interactions can lead to a positive Δ ads S under certain adsorption conditions. However, the influence of chain conformation on Δ ads S is found to correlate more directly with the manner in which the unique states of the system are distributed among the energy levels available to the adsorbed chain. Δ ads S is found to tend toward a maximum for adsorption processes described by thermally averaged energy landscapes in which the energy levels carrying the highest Boltzmann weights have a high degree of conformational degeneracy. This condition is met when the average interaction energy between the chain and the sorbent equals that between two hydrophobic segments of the chain.
Keywords: Protein adsorption; Protein stability; Thermodynamics; Conformational entropy; Dynamic Monte Carlo simulations;

Modeling the mechanism involved during the sorption of methylene blue onto fly ash by K. Vasanth Kumar; V. Ramamurthi; S. Sivanesan (14-21).
Batch sorption experiments were carried out to remove methylene blue from its aqueous solutions using fly ash as an adsorbent. Operating variables studied were initial dye concentration, fly ash mass, pH, and contact time. Maximum color removal was observed at a basic pH of 8. Equilibrium data were represented well by a Langmuir isotherm equation with a monolayer sorption capacity of 5.718 mg/g. Sorption data were fitted to both Lagergren first-order and pseudo-second-order kinetic models and the data were found to follow pseudo-second-order kinetics. Rate constants at different initial concentrations were estimated. The process mechanism was found to be complex, consisting of both surface adsorption and pore diffusion. The effective diffusion parameter D i values were estimated at different initial concentrations and the average value was determined to be 2.063 × 10 −9 cm 2 / s . Analysis of sorption data using a Boyd plot confirms the particle diffusion as the rate-limiting step for the dye concentration ranges studied in the present investigation (20 to 60 mg/L).
Keywords: Adsorption; Malachite green; Adsorption kinetics; Equilibrium; Mechanisms;

Heavy metals in wastes exist as multiple pollutants. The study of the interactions between multiple pollutants and soils should be of significance in practice. In the present study, the effect of chromate on adsorption and desorption behavior of Cu(II) in two variable charge soils was investigated, with the emphasis on the adsorption and desorption equilibria of Cu(II). The results showed that chromate can affect adsorption and desorption of Cu(II) in the colloidal systems of two variable charge soils. The extent of the effect was related to the initial concentrations of chromate and Cu(II), the system pH, and the nature of the soils. The presence of chromate led to an increase in the adsorption of Cu(II). For example, in the presence of 0.5, 0.8, 1.0, and 1.5 mmol L−1 of chromate, for the rhodic ferralsol the adsorption of Cu(II) increased by 15.3, 18.0, 19.0, and 20.2%, respectively. For the hyperrhodic ferrasol, the corresponding figures were 11.9, 17.0, 20.3, and 26.1%, respectively. The presence of chromate also caused an increase in the desorption of Cu(II). For instance, in the presence of 0.5, 1.0, and 1.5 mmol L−1 of chromate, the desorption for the rhodic ferralsol increased by 16.9, 27.5, and 34.1%, respectively. For the hyperrhodic ferralsol, the corresponding figures were 18.1, 35.6, and 51.4%, respectively. The increments of the adsorption and desorption increased with the increase in equilibrium concentration of Cu(II) in the solution. For instance, when the equilibrium concentrations were 0.5, 1.0, 1.5, and 2.0 mmol L−1, the increments for the rhodic ferralsol were 2.5, 3.2, 3.3, and 3.0 mmol kg−1, respectively. For the hyperrhodic ferralsol, the corresponding figures were 2.9, 3.5, 4.0, and 4.2 mmol kg−1, respectively. The effect of chromate for the hyperrhodic ferralsol was greater than that for the rhodic ferralsol. This is caused by the difference in the content of iron oxides for the two soils. The increments of the adsorption and the desorption of Cu(II) increased with the rise in pH, reaching a maximum value, and then decreased. It can be assumed that the increment of the adsorption was caused by the change in surface charge of the soils induced by the adsorption of chromate and the cooperative adsorption of chromate adsorbed and Cu(II). The increase of electrostatically adsorbed Cu(II) was responsible for the increase in the desorption of Cu(II).
Keywords: Chromate; Cu(II); Adsorption; Desorption; Variable charge soil;

The pHpzc values of several mechanical mixtures of amorphous hydrous oxides of iron (amorphous FeOOH) and manganese (δ-MnO2) have been determined using the solid addition method. While the pHpzc of δ-MnO2 remains almost unchanged, the corresponding value for amorphous FeOOH tends to increase with increased proportion of δ-MnO2 in the mixtures. The adsorption behavior of Co2+, Ni2+, Cu2+, and Zn2+ with respect to pH on a mechanical mixture of 70% δ-MnO2 and 30% amorphous FeOOH from 0.5 M NaCl and major ion sea water has been studied. Since δ-MnO2 is much more active adsorbent than amorphous FeOOH at pH below 6.5, the adsorption data on mixture have not only been normalized with respect to the mass of δ-MnO2 in the mixture, but also compared with adsorption data on δ-MnO2 alone. It is interesting to note that though each trace metal behaves in a different way from the other especially with respect to the nature of electrolyte medium, it is generally observed that the adsorption on the mixed oxide system is higher than that on δ-MnO2 alone under similar condition. It is also observed that adsorption in major ion sea water at a particular pH value is lower than in 0.5 M NaCl solution.
Keywords: Adsorption; Metal ions; Mixture of δ-MnO2 and amorphous FeOOH; Sea water;

Carbon–mineral adsorbents prepared by pyrolysis of waste materials in the presence of tetrachloromethane by Roman Leboda; Barbara Charmas; Jadwiga Skubiszewska-Zięba; Stanislaw Chodorowski; Patryk Oleszczuk; Vladimir M. Gun'ko; Valery A. Pokrovskiy (39-47).
Natural bentonite spent in the process of plant oil bleaching was used as an initial material for preparation of carbon–mineral adsorbents. The spent bleaching earth was treated using four procedures: T (thermal treatment); H (hydrothermal treatment); C (thermal treatment with addition of CCl4 vapor); M (modification of porous structure). Raw bentonite, RB (raw bleaching earth), and carbon materials prepared using plant oil were compared. The physicochemical characteristics of the adsorbents were determined using different methods: nitrogen adsorption/desorption, XRD, TEM, and MS-TPD. Carbon–mineral adsorbents contain from 5.23 to 19.92% C (w/w) and carbon adsorbents include from 84.2 to 91.18% C (w/w). Parallel processes of organic substance carbonization, porous structure modification, sublimation or evaporation of metal chlorides, and removal of hydrogen chloride take place during pyrolysis of waste mineral materials in the CCl4 atmosphere.
Keywords: Waste materials; Pyrolysis; Carbon–mineral adsorbents; Utilization;

Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff by M. Rožić; Š. Cerjan-Stefanović; S. Kurajica; M. Rožmarić Maěefat; K. Margeta; A. Farkaš (48-56).
The paper presents results of investigation of exchange of the clinoptilolite tuff cations with hydrogen ions from HCl solution of concentration 0.1 mmol cm−3 and ammonium ions solutions of concentrations 0.0071 to 2.6 mmol cm−3. Molal concentrations, x (mmol g−1) of cations exchanged in acid solution and in ammonium ions solutions were compared with molal concentrations of cations obtained by determination of the cation-exchange capacity of clinoptilolite tuff. The obtained results show that at ammonium ion concentrations lower than 0.1 mmol cm−3, with regard to exchange capacity for particular ions, best exchanged are Na+ ions, followed by Mg2+ and Ca2+ ions, while exchange of K+ ions is the poorest (Na+  > Mg2+  > Ca2+  > K+). At ammonium concentrations from 0.2 to 1 mmol cm−3 the order is Na+  > Ca2+  > Mg2+> K+. At concentrations higher than 1 mmol cm−3 the order is Na+  > Ca2+  > K+  > Mg2+. The results are a consequence of the uptake of hydrogen ions by zeolite samples in ammonium ions solutions at concentrations lower than 1 mmol cm−3 and indicate the importance of Mg2+ (besides Na+ ions) for the exchange between clinoptilolite cations and H+ ions, in contrast to K+ ions, whose participation in the reaction with H+ ions is the lowest. During decationization of the clinoptilolite in acid solution, best exchanged are Na+, Mg2+, and Ca2+ ions, while exchange of K+ ions is the poorest. Due to poor exchange of K+ and H+ ions and good exchange of Na+, Mg2+, and Ca2+ ions, it is to be assumed that preservation of stability of the clinoptilolite structure is caused by K+ ions present in the channel C. Clinoptilolite is dissolved in the clinoptilolite A and B channels where Na+, Mg2+, and Ca2+ ions are present. On the acid-modified clinoptilolite samples, exchange of ammonium ions is poorer than on natural zeolite. The longer the contact time of the zeolite and acid solution, the worse ammonium ions exchange. It can be assumed that H+ ions exchanged with zeolite cations are consumed for solution of aluminum in the clinoptilolite structure; therefore the concentration of H+ ions as exchangeable cations decreases. In the ammonium ion solution at a concentration of 0.0065 mmol cm−3, from the acid-modified zeolite samples, Al3+ ions are exchanged best, followed by Na+, Mg2+, Ca2+, and K+ ions. Further to the results, it is to be assumed that exchangeable Al3+ ions available from clinoptilolite dissolution are best exchanged with H+ ions in acid solution.
Keywords: Clinoptilolite; Hydrogen ions; Ammonium; Ion exchange;

Scale inhibition study by turbidity measurement by V. Tantayakom; T. Sreethawong; H. Scott Fogler; F.F. de Moraes; S. Chavadej (57-65).
The concept of a critical supersaturation ratio (CSSR) has been used to characterize the effectiveness of different types of scale inhibitors, inhibitor concentration, and precipitating solution pH in order to prevent the formation of barium sulfate scale. The scale inhibitors used in this work were aminotrimethylene phosphonic acid (ATMP), diethylenetriaminepentamethylene phosphonic acid (DTPMP), and phosphinopolycarboxylic acid polymer (PPCA). The CSSR at which barium sulfate precipitates was obtained as a function of time for different precipitation conditions and was used as an index to evaluate the effect of the precipitation conditions. The results showed that the CSSRs decrease with increasing elapsed time after mixing the precipitating solutions, but increases with increasing scale inhibitor concentration and solution pH. The CSSR varies linearly with the log of the scale inhibitor concentration and with the precipitating solution pH. A SEM analysis showed that the higher the scale inhibitor concentration and solution pH, the smaller and more spherical the BaSO4 precipitates. Analysis of the particle size distribution revealed that increasing the elapsed time, the scale inhibitor concentration, and precipitating solution pH, all produce a broader particle size distribution and a smaller mean diameter of the BaSO4 precipitates. DTPMP and PPCA were the most effective BaSO4 scale inhibitors per ionizable proton and the most effective on a concentration basis, respectively.
Keywords: Barium sulfate; Inhibition; Precipitation; Nucleation;

Structural and adsorptive properties of Ba or Mg oxide modified zirconia by Aiguo Liu; Kafui Nyavor; Ramble Ankumah (66-70).
Zirconia nanoparticles modified by barium oxide or magnesium oxide were synthesized by using a co-precipitation process followed by ethanol supercritical drying. The nanoparticles obtained were further calcined at 873 K. BET surface area, XRD, and TGA were used to characterize the prepared samples. Isotherms of N2 and CO2 adsorption on these modified zirconia nanoparticles were measured at various temperatures. Additions of BaO or MgO resulted in an increase in CO2 adsorption capacity of the modified zirconia particles. Results also show that BaO as a modifier is more effective than MgO in enhancing the CO2 adsorption capacity of zirconia. At 1 bar and 473 K, Ba modified zirconia adsorbs ∼0.25 mmol/g of CO2.
Keywords: Zirconia; CO2 adsorption; Nanoparticle; Magnesium oxide; Barium oxide; Light gas separation;

A novel type adsorbent was prepared by in situ precipitation of Fe(OH)3 on the surface of activated Al2O3 as a support material. The iron content of the adsorbent was 0.31 ± 0.003 %   m/m (56.1 mmol/g); its mechanical and chemical stability proved to be appropriate in solutions. The total capacity of the adsorbent was 0.12 mmol/g, and the pH of zero point of charge, pHzpc = 6.9 ± 0.3 . Depending on the pH of solutions, the adsorbent can be used for binding of both anions and cations, if pHeq  < pHzpc anions are sorbed on the surface of adsorbent (S) through {S― OH 2 + } and {S―OH} groups. A graphical method was used for the determination of pHiep (isoelectric points) of the adsorbent and values of pHiep = 6.1 ± 0.3 for As(III) and pHiep = 8.0 ± 0.3 for As(V) ions were found. The amount of surface charged groups (Q) was about zero within the a pH range of 6.5–8.6, due to the practically neutral surface formed on the adsorption of As(V) ions. At acidic pH (pH 4.7), Q = 0.19   mol / kg was obtained. The adsorption of arsenate and arsenite ions from solutions of 0.1–0.4 mmol/L was represented by Langmuir-type isotherms. A great advantage of the adsorbent is that it can be used in adsorption columns, and low waste technology for removal of arsenic from drinking water can be developed.
Keywords: Iron hydroxide; Alumina; Arsenate; Arsenite; Adsorption; Isotherms; Zero point of charge; Isoelectric points;

Adsorption of methylene blue onto jute fiber carbon: kinetics and equilibrium studies by S. Senthilkumaar; P.R. Varadarajan; K. Porkodi; C.V. Subbhuraam (78-82).
Jute fiber obtained from the stem of a plant was used to prepare activated carbon using phosphoric acid. Feasibility of employing this jute fiber activated carbon (JFC) for the removal of Methylene blue (MB) from aqueous solution was investigated. The adsorption of MB on JFC has found to dependent on contact time, MB concentration and pH. Experimental result follows Langmuir isotherm model and the capacity was found to be 225.64 mg/g. The optimum pH for the MB removal was found to be 5–10. The kinetic data obtained at different concentrations have been analyzed using a pseudo-first-order, pseudo-second-order equation, intraparticle diffusion and Elovich equation. Among the kinetic models studied, the intraparticle diffusion was the best applicable model to describe the adsorption of MB onto JFC.
Keywords: Activated carbon; Methylene blue; Adsorption isotherm; Equilibrium studies; Kinetic models;

Adsorption of benzoic acid onto high specific area activated carbon cloth by Erol Ayranci; Numan Hoda; Edip Bayram (83-88).
The adsorption of benzoic acid from aqueous solution onto high area carbon cloth at different pH values has been studied. Over a period of 125 min the adsorption process was found to follow a first-order kinetics and the rate constants were determined for the adsorption of benzoic acid at pH 2.0, 3.7, 5.3, 9.1, and 11.0. The extents of adsorption and the percentage coverage of carbon cloth surfaces were calculated at 125 min of adsorption. Adsorption isotherms at pH values of 2.0, 3.7, and 11.0 were derived at 25 °C. Isotherm data were treated according to Langmuir and Freundlich equations and the parameters of these equations were evaluated by regression analysis. The fit of experimental isotherm data to both equations was good. It was found that both the adsorption rate and the extent of adsorption at 125 min were the highest at pH 3.7 and decreased at higher or lower pH values. The types of interactions governing in the adsorption processes are discussed considering the surface charge and the dissociation of benzoic acid at different pH values.
Keywords: Adsorption; Benzoic acid; Carbon cloth; Surface charge;

Bottom ash, a power plant waste, and de-oiled soya, an agricultural waste material, were employed for the removal and recovery of Quinoline Yellow, a water-soluble dye. Characterization of adsorbent materials was made by their infrared and differential thermal analysis curves. Along with batch adsorption studies, which involve effect of pH, adsorbate concentration, sieve size, adsorbent dosage, contact time, temperature, etc., kinetic studies and column operations were also made to remove the dye from wastewater. On the basis of kinetic studies, specific rate constants involved in the processes were calculated and first-order adsorption kinetics was observed in both the cases. The paper also incorporates Langmuir and Freundlich adsorption isotherm models, which are used to calculate thermodynamic parameters and also to suggest a plausible mechanism of the ongoing adsorption processes. Fixed bed columns were prepared for both the adsorbents and bulk removal of the dye was achieved by eluting aqueous solution of the dye and saturation factor for both columns were evaluated. Dilute NaOH solution was then percolated through the exhausted columns to recover the adsorbed dye.
Keywords: Adsorption; Bottom ash; De-oiled soya; Quinoline Yellow; Dyes;

Enzymatic degradation of model cellulose films by Jonny Eriksson; Martin Malmsten; Fredrik Tiberg; Thomas Hønger Callisen; Ture Damhus; Katja S. Johansen (99-106).
Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated.
Keywords: Ellipsometry; Cellulose model surface; Spin coating; Adsorption; Cellulase; Enzymatic degradation;

Combined study of X-ray reflectivity and atomic force microscopy on a surface-grafted phospholipid monolayer on a solid by Kwangmeyung Kim; Youngro Byun; Chulhee Kim; Tae Chul Kim; Do Young Noh; Kwanwoo Shin (107-113).
We investigated the detailed structure of a surface-grafted phospholipid monolayer, which was polymerized in situ onto a methacryloyl-silanized solid surface. By the combined study of X-ray reflectivity and atomic force microscopy, the in situ polymerization step of the lipid molecules are sufficiently detailed to reveal the molecular structure of lipid molecules before and after in situ polymerization. From the data of the X-ray reflectivity, we confirmed that the in situ polymerization process produces a flat lipid monolayer structure and that the lipid monolayer is substantially grafted on a silanized surface by chemical bonding. After the polymerization and washing processes, the thickness of the head group was 9 Å and the thickness of the tail group was 21 Å. The surface morphology of the polymerized phospholipid monolayer obtained by the measurements of atomic force microscopy was consistent with the results of the X-ray reflectivity. The cross-sectional analysis shows that the surface coverage of lipid molecules, which are chemically grafted onto a silanized surface, is approximately 89%.
Keywords: Phospholipid monolayer; In situ polymerization; X-ray reflectivity; Atomic force microscopy;

A supramolecular assembly of phospholipid-polymerized diacetylene vesicles functionalized with glycolipid can provide a molecular recognition function. The Escherichia coli–glycolipid binding event leads to a visible color change from blue to red, readily seen with the naked eye and quantified by absorption spectroscopy. The biosensor signal is amplified through a suitable increase of phospholipid content in the mixed lipid vesicles and pH of aqueous solutions.
Keywords: Polydiacetylene vesicle; Glycolipid; Detection of E. coli;

Film formation from monodisperse acrylic latices by Shiva Zohrehvand; Rong Cai; Bart Reuvers; Klaas te Nijenhuis; Abe Posthuma de Boer (120-128).
The influence of concentration and layer thickness on particle ordering in polymer latex films, both open and closed, has been studied by means of rheology, microscopy and turbidimetry. Monodisperse acrylic latices were synthesized by semicontinuous emulsion polymerization. The latices exhibited a distinct thixotropy above a certain concentration, which is attributed to crystallization. Microscopy revealed a three-layer structure and a dependence of crystal size and crystal packing on layer thickness and layer concentration. Turbidimetry (i.e., analysis of light transmission and interference) was used to study the progress of ordering in open and closed systems. In closed films crystallization proceeds faster at higher concentrations and in thinner films. Above a sufficiently high concentration no crystallization was observed. Furthermore, an induction time was found below certain concentrations. The drying of open latex films at temperatures below the minimum film formation temperature (MFFT) was shown to proceed through five distinct stages. The drying of open films at temperatures below the MFFT was studied by analysis of the turbidity of rewetted films. A more compact structure was found in thinner films. The structure in latices is discussed as a result of long-range and short-range ordering.
Keywords: Film formation; Monodisperse latices; Rheology; Microscopy; Turbidimetry; Interference; Particle ordering; Colloidal crystals;

Film formation from monodisperse acrylic latices by Klaas te Nijenhuis; Shiva Zohrehvand (129-138).
The influence of drying temperature on the properties of latex films was investigated by gravimetry, turbidimetry (i.e., analysis of transmission spectra and interference), atomic force microscopy and measurement of water vapor permeability. Several pitfalls in the determination of water content of dried films that absorb water after being submerged in it have been proposed, such as fading boundaries, remaining water after drying and change of particle sizes. At moderately higher temperatures film formation is improved. This improvement follows from the formation of smoother film surfaces (AFM), lower water vapor permeabilities and smaller values for Δ λ min . On the other hand, defects as cracks and channels also are created, especially at high temperatures. It appears, however, that these channels do not run from the one surface of a film to the other.
Keywords: Film formation; Monodisperse latices; Turbidimetry; Transmission; Interference; Permeability; Atomic force microscopy; Water immersion; Water absorption; Remaining water;

Hofmeister effects on the colloidal stability of an IgG-coated polystyrene latex by T. López-León; A.B. Jódar-Reyes; J.L. Ortega-Vinuesa; D. Bastos-González (139-148).
The effect of various ions related to the Hofmeister series (HS) on different properties of a cationic latex covered with a protein (IgG) is analyzed in this study. NaNO3, NH4NO3, and Ca(NO3)2 were used to compare the specificity of the cations, and NaCl, NaSCN, NaNO3, and Na2SO4, to compare the specificity of the anions. Two pH values, 4 and 10, were chosen to analyze the behavior of these ions acting as counter- and co-ions. At pH 4, the total surface charge is positive, whereas at pH 10 it is negative. Three different phenomena have been studied in the presence of these Hofmeister ions: (1) colloidal aggregation, (2) electrophoretic mobility, and (3) colloidal restabilization. The specific effect of the ions was clearly observed in all experiments, obtaining ion sequences ordered according to their specificity. The most important parameter for ion ordering was the sign of the charge of the colloidal particle. Positively charged particles displayed an ion order opposite that observed for negatively charged surfaces. Another influential factor was the hydrophobic/hydrophilic character of the particle surface. IgG–latex particle surfaces at pH 10 were more hydrophilic than those at pH 4. The SCN ion had a peculiar specific effect on the phenomena studied (1)–(3) at pH 10. With respect to the restabilization studies at high ionic strengths, new interesting results were obtained. Whereas it is commonly known that cations may provoke colloidal restabilization in negative particles when they act as counterions, our experiments demonstrated that such restabilization is also possible with positively charged particles. Likewise, restabilization of negative surfaces induced by the specific effect of chaotropic anions (acting as co-ions) was also observed.
Keywords: Hofmeister series; Colloidal stability; Restabilization by hydration forces;

The molecular mechanism of montmorillonite flocculation by bacterial polysaccharides was investigated, with special emphasis on the effect of carboxylic charges in the macromolecules on the mechanisms of interaction with the clay surface. An indirect way to quantify the energy of interaction was used, by comparing the flocculation ability of variously acidic polysaccharides. Data on tensile strength of aggregates in diluted suspension were collected by timed size measurements in the domain 0.1–600 μm, using laser diffraction. The flow behavior of settled aggregates was studied by rheology measurements. Flocculation of colloidal clay suspension by polysaccharides requires canceling of the electrostatic repulsions by salts, which allows approach of clay surfaces close enough to be bridged by adsorbing macromolecules. The amount of acidic charges of the polysaccharides, and especially their location in the molecular structure, governs the bridging mechanism and the resulting tensile strength of the aggregates. The exposure of carboxylate groups located on side chains strongly promotes flocculation. In turn, charges located on the backbone of the polysaccharide are less accessible to interaction, and the flocculation ability of such polysaccharides is lowered. Measurements at different pH indicate that adsorption of acidic polysaccharides occurs via electrostatic interactions on the amphoteric edge surface of clay platelets, whereas neutral polysaccharides rather adsorb via weak interactions. Increased tensile strength in diluted aggregates due to strong surface interactions results in proportionally increased viscosity of the concentrated aggregates.
Keywords: Montmorillonite; Polysaccharides; Aggregation; Coagulation; Charge; Structure;

The gradient diffusion coefficients of recombinant human lactoferrin, a glycoprotein that is of commercial interest, have been extensively investigated theoretically and experimentally. A theoretical prediction was developed to allow calculation of the thermodynamic coefficient in terms of the electrostatic repulsive forces, London–van der Waals forces, entropic forces and additional interactions of unknown source and determination of the hydrodynamic coefficient by a perturbation theory method. In addition, dilute limit calculations were carried out for both of them. The thermodynamic and hydrodynamic coefficients were incorporated in the generalised Stokes–Einstein equation to calculate the gradient diffusion coefficient. Dynamic light scattering experiments were also conducted under different physiochemical conditions in which the gradient diffusion coefficients and the mean sizes of the macromolecules were measured. It was shown that of the theoretical approaches studied, good quantitative agreement between theory and experiment was found.
Keywords: Gradient diffusion coefficient; Dynamic light scattering; Colloidal dispersion; Interparticle interactions;

The main objective of this study was to synthesize novel demulsifiers for resolving oil-in-water emulsions. Diethanolamine polyethers are considered as a cationic polymer type. The study describes an improved synthesis of a series of diethanolamine polyethers via condensation of 3–7 or 9 mol of diethanolamine. The structure and the molecular weights of the major components in the reaction mixture were confirmed via IR and MS analyses. The demulsifiers were used for treatment of pollution in the refinery wastewater with or without FeCl3. The flocculation efficiency of the synthesized demulsifiers was determined by turbidity measurement of the treated and untreated O/W emulsion in the Cairo Oil Refinery Company. The critical flocculation concentration (CFC) and charge density of the synthesized demulsifiers were determined. Biodegradation of diethanolamine polyethers was measured in river water within 7–8 days.
Keywords: Diethanolamine polyether; Cationic emulsion breakers; Chemical destabilization; Condensation polymerization;

Investigation of the interfacial properties of water-in-diluted-bitumen emulsions using micropipette techniques by Christina Tsamantakis; Jacob Masliyah; Anthony Yeung; Thomas Gentzis (176-183).
The interfacial properties of water-in-diluted bitumen emulsions were studied using micropipette techniques. It was observed that, as bitumen concentration in the bulk phase ( C 0 ) increased, the interfacial tension on the water droplet surfaces decreased. In addition, there was a small effect on the interfacial tension when different solvent mixtures were used. Mixtures of toluene and heptane in different ratios were used as solvents for bitumen dilution. Crumpling of the interface was influenced by bitumen concentration and type of solvent. No crumpling was found for bitumen content less than 0.01% for all solvents used. Crumpling was observed at higher bitumen concentrations when deionized water (pH 5.4–5.6) was used. Setting “heptol[A]” to be the mixture of toluene and heptane, with the volume percent of toluene being A, the following were concluded. Crumpling disappeared at C 0 > 1 % and when heptol[100] was used, and also at C 0 > 10 % and when heptol[30] was used. Crumpling was strongly affected by the water pH. In the case of heptol[50], at a higher pH, the crumpling region that normally occurred at C 0 > 0.01 % disappeared. The micropipette technique proved to be useful in studying the interfacial properties of micrometer-sized emulsion drops.
Keywords: Micropipette; Interfacial properties; Water-in-bitumen emulsions; Athabasca bitumen; Canada;

ZnO nanoparticles with spherical morphology and narrow size distribution were obtained by calcination of Zn(OH)2 nanoparticles, which were prepared in a polyethylene glycol mono-4-nonylphenyl ether (NP-5)/cyclohexane reverse micellar system and incorporated into polyurea (PUA) via an in situ polymerization of hexamethylene diisocyanate (HDI). The resulting ZnO nanoparticles demonstrated a near-UV emission and a green emission, the intensity ratio of which depended on calcination conditions. For the nanoparticles studied, the calcination atmosphere influenced remarkably the photoluminescence properties such as intensity ratio of the near-UV emission to green emission, rather than the size, morphology, and crystallinity of the ZnO nanoparticles. The green emission decreased by calcination in O2 flow but increased by calcination in N2 flow, as compared with the case calcined in air flow. This finding suggests that the green emission is enhanced with the increase of the number of oxygen vacancies of the ZnO nanoparticles and thus the photoluminescence properties of the nanoparticles were successfully controlled by the calcination condition, without changing the size and morphology.
Keywords: ZnO nanoparticles; Reverse micelles; Photoluminescence properties;

Recovery of nanoparticles produced in phosphatidylcholine-based template phases by J. Koetz; S. Reichelt; S. Kosmella; B. Tiersch (190-198).
This paper focuses on the characterization and use of polymer-modified phosphatidylcholine (PC)/sodium dodecyl sulfate (SDS)-based inverse microemulsions as a template phase for BaSO4 nanoparticle formation. The area of the optically clear inverse microemulsion phase in the isooctane/hexanol/water/PC/SDS system is not significantly changed by adding polyelectrolytes, i.e., poly(diallyldimethylammonium chloride) (PDADMAC), or amphoteric copolymers of diallyldimethylammonium chloride and maleamid acid to the SDS-modified inverse microemulsion. Shear experiments show non-Newtonian flow behavior and oscillation experiments show a frequency-dependent viscosity increase (dilatant behavior) of the microemulsions. Small amounts of bulk water were identified by means of differential scanning calorimetry. One can conclude that the macromolecules are incorporated into the individual droplets, and polymer-filled microemulsions are formed. The polymer-filled microemulsions were used as a template phase for the synthesis of BaSO4 nanoparticles. After solvent evaporation the nanoparticles were redispersed in water and isooctane, respectively. The polymers incorporated into the microemulsion are involved in the redispersion process and influence the size and shape of the redispersed BaSO4 particles in a specific way. The crystallization process mainly depends on the type of solvent and the polymer component added. In the presence of the cationic polyelectrolyte PDADMAC the crystallization to larger cubic crystals is inhibited, and layers consisting of polymer-stabilized spherical nanoparticles of BaSO4 (6 nm in size) will be observed.
Keywords: Microemulsions; Nanoparticles; Phosphatidylcholine; Phase behavior; Polyelectrolytes;

Preparation of gold–, gold/silver–dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation by Kunio Esumi; Takashi Matsumoto; Yuusuke Seto; Tomokazu Yoshimura (199-203).
Gold– and gold/silver–dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver–dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal–dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.
Keywords: Gold–dendrimer nanocomposite; Gold/silver–dendrimer nanocomposites; UV irradiation; Benzoin;

The effects of chemical treatments on red mud (RM) were investigated in terms of thermal stabilities of PMMA/RM and PVC/RM nanocomposites. N2/77 K adsorption behavior and contact angles were studied in the pore structures and surface energetics of RM, respectively. Thermal stabilities of the nanocomposites were investigated using a thermal mechanical analyzer (TMA) and thermogravimetric analysis (TGA). As a result, the acidically treated RM (ARM) had higher adsorption properties, including specific surface area, than untreated RM (VRM) or basically treated RM (BRM). A change in the structure of the ARM surface was due to hydrolysis or leaching a metal salt out of RM. Also, the electron acceptor ( γ S + , acid) of ARM and the electron donor ( γ S − , base) of BRM were increased in the development of acid and basic functional groups, respectively. PMMA/ARM nanocomposites had higher thermal stability and mechanical interfacial properties than PMMA/VRM or BRM nanocomposites. These results were due to the improvements of the dispersion properties and acid–base interfacial interactions of basic PMMA and ARM. In this work, although the dispersion properties of the BRM decreased, the thermal stabilities and mechanical interfacial properties of PVC/BRM nanocomposites increased, which could be attributed to improvement in the interfacial interactions between acidic PVC and BRM.
Keywords: Red mud; Chemical surface treatment; Electron acceptor–donor; Thermal stabilities; Surface energetics;

Electrical double-layer effects on the deposition of zeolite A on surfaces by Bovornlak Oonkhanond; Michael E. Mullins (210-215).
Zeolite particles formed from an aluminosilicate solution possess a negative surface charge due to the substitution of aluminum atoms into a SiO4 tetrahedral structure making it difficult to form a continuous layer in solution. The particle interactions with surfaces and each other can be studied using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The interaction energy between zeolite–zeolite and zeolite–substrate on various materials can be estimated in this fashion. The zeolite LTA particles show a stronger repulsion interaction on all substrates and on the each other as compared to the ZSM-5 particles. This repulsive energy also increases as the particles size increases. This results in the formation of conglomerate in the solution rather than forming an adhered layer on the substrate.
Keywords: Zeolite LTA; Zeolite ZSM-5; DLVO; Repulsive energy; London–Van der Waals; Alumina substrate;

Covalent assembly of shortened multiwall carbon nanotubes on polyelectrolyte films and relevant electrochemistry study by Yang Lan; Enbo Wang; Yonghai Song; Zhenhui Kang; Min Jiang; Lei Gao; Suoyuan Lian; Di Wu; Lin Xu; Zhuang Li (216-221).
A significant and versatile approach was developed for perpendicularly aligning multiwall carbon nanotubes on diverse substrates suitable for layer-by-layer self-assembly. The multiwall carbon nanotubes (s-MWNTs) used were shortened with oxidation under ultrasonic and functionalized with acyl chloride in thionyl chloride (SOCl2). The monolayer of s-MWNTs perpendicularly grafted to the substrate was obtained by dipping the polyelectrolyte modifying substrate into a tetrahydrofuran suspension of the functionalized s-MWNTs. The interaction proved to be stable and not liable to be affected by the ambience. Transmission electron microscopy and atomic force microscopy were used to examine the morphology of the MWNTs and s-MWNTs grafted on the substrates. Raman spectroscopy was applied to verify the existence of s-MWNTs for assembly, and Fourier transform infrared absorption spectra were used to investigate the interaction pattern between s-MWNTs and polyelectrolyte. The electrochemistry properties of the monolayer of s-MWNTs when the substrate was indium–tin oxide were studied.
Keywords: Multiwall carbon nanotube; Polyelectrolyte; Electrochemistry; Covalent bond; Layer-by-layer; Indium–tin oxide;

Effect of drying on the mesoporous structure of sol–gel derived silica with PPO–PEO–PPO template block copolymer by Lihua Pei; Ken-ichi Kurumada; Masataka Tanigaki; Masahiko Hiro; Kenzo Susa (222-227).
The effects of drying method on the pore structure of mesoporous silica were studied from the viewpoint of enhancing closed porosity in mesoporous silica. The mesoporous silica was prepared via a sol–gel process using polyethyleneoxide–polypropyleneoxide–polyethyleneoxide (PEO–PPO–PEO) triblock copolymer (Pluronic P123) as the structure-directing template. The closed porosity was evaluated from the apparent mass density of the sample measured by a helium pycnometer. These mesoporous silicas were also characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and nitrogen adsorption. The drying method was shown to be responsible for the finally templated mesoporous structure of the silica. More rapid drying is more preferable for enhancing the closed porosity of the mesoporous silica. The closed pores were formed by immediate immobilization of copolymer molecular assemblies in the silica matrix due to the instant removal of the solvent and solidification at higher temperatures. The drying method, mainly affecting the drying rate, is highly influential on the finally replicated mesoporous structure in silica.
Keywords: Mesoporous silica; Drying method; Block copolymer; Templating; Closed porosity;

Although an amount of research has reported that a flux minimum occurrs at the isoionic/isoelectric points (pH 4.6–5.0) in the absence of salts in the ultrafiltration of bovine serum albumin (BSA), the real mechanism remains incompletely understood due to the lack of additional techniques in real time to detect the properties of deposited BSA (gel) layers formed during ultrafiltration (UF). An ultrasonic technique was developed as an analytical noninvasive tool to in situ investigate the properties of deposited BSA layers at pH 4.9 (isoionic or isoelectric point, IEP) and 6.9 during crossflow ultrafiltration. The membrane was a polysulfone (PSf) UF membrane with molecular weight cut-off (MWCO) 35 kDa. The feed used was 0.5 g/l BSA solution. Results show good correspondence between the ultrasonic signal responses and the development of BSA gel layers on the membranes. The deposit is thicker at pH 6.9 than at pH 4.9. However, the deposited gel layers are more compressible at pH 4.9 than at pH 6.9. The flux decline is mainly controlled by the density (packing) of the deposit layer. At pH 6.9, protein mainly deposits on the membrane surface. Around the isoelectric point, protein absorbs within and on the membranes. A functional relationship between acoustic signals and fouling resistance exists. The fouling resistance is mainly attributed to pore blocking or pore constriction.
Keywords: Ultrasonic technique; Bovine serum albumin; Protein deposition; Ultrafiltration; Fouling; Isoelectric point;

Effect of the intercalation conditions of a montmorillonite with octadecylamine by A. Pérez-Santano; R. Trujillano; C. Belver; A. Gil; M.A. Vicente (239-244).
Intercalation of montmorillonite with octadecylamine under several conditions is reported. Octadecylamine was protonated in situ with HCl to obtain octadecylammonium cations. Water and water/ethanol mixtures were used as reaction medium, and the ratios amine/clay and HCl/amine were also varied. Intercalation was successful when the amine/clay ratio was in the range 1–3 mmol/g; optimal results were obtained for an amine/clay ratio of 2.0 mmol/g. For a given amine/clay ratio, the HCl/amine ratio also influences the intercalation. Basal spacings of the intercalated solids were between 13.4–36.7 Å. The amount of organic matter incorporated into the solids also varied widely; up to 40 wt% is fixed. Specific surface area is very low in all the intercalated solids because of the blockage of the clay porosity by the organic molecules. Co-intercalation of octadecylammonium and of the inorganic polycation [Al13O4(OH)24(H2O)12]7+ was also considered, giving rise to intercalated solids with basal spacings between 17 and 22 Å, also with a high fixation of organic matter.
Keywords: Montmorillonite; Octadecylammonium; Intercalation;

Observation and modelling of clamshell droplets on vertical fibres subjected to gravitational and drag forces by Benjamin J. Mullins; Roger D. Braddock; Igor E. Agranovski; Roger A. Cropp; Rebecca A. O'Leary (245-254).
Extensive experimental investigation of the wetting processes of fibre–liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment of drops from fibres as airflow velocity increases, and also movement or flow of droplets along fibres. A detailed experimental study of the processes was conducted using stainless steel filter fibres and H2O aerosol, which coalesce on the fibre to form clamshell droplets. The droplets were predominantly observed in the Reynolds transition flow region, since this is the region where most of the above features occur. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as the increasing droplet size increases Reynolds number for the flow around the droplet. Two-dimensional flow in this region is usually modelled using the classical Karman vortex street, however there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is very good for both the radial and transverse oscillations.
Keywords: Fibre wetting; Drag; Filtration; Liquid aerosols;

Adsorption isotherms of binary aqueous solutions of methanol, ethanol, 1-propanol, 2-propanol, tert-butanol, and 1-butanol are demonstrated, being calculated by using the Gibbs adsorption equation with experimental data of surface tension and vapor pressure found in the literature. For all of the alcohol–water mixtures, the maximum value in the adsorption isotherm, namely, the maximum surface excess is about that expected for the formation of a monolayer. Furthermore, the composition of the mixture for the maximum surface excess coincides with that corresponding to the minimum in the excess partial molar volume of the solutes. These results indicate that the hydrophobic hydration in bulk induces the surface excess of the alcohols and after a monolayer is formed, the hydrophobic hydration itself is no longer retained.
Keywords: Surface structure; Alcohol–water mixtures; Adsorption isotherm; Hydrophobic hydration; Surface tension; Activity; Monolayer; Surface excess; Partial molar volume; Gibbs adsorption equation;

Capillary rise kinetics of some building materials by M. Karoglou; A. Moropoulou; A. Giakoumaki; M.K. Krokida (260-264).
The presence of water in masonry is one of the main factors in deterioration. Capillary rise is the most usual mechanism of water penetration into building materials. In this study the kinetics of the capillary rise phenomenon was studied for various building materials: four stones, two bricks, and six plasters. A first-order kinetic model was proposed, in which the equilibrium moisture height derived from Darcy law. The capillary height time constant found to be strongly affected by the material characteristics. Moreover, the capillary height time constant can be predicted if the average pore radius of the materials is known.
Keywords: Brick; Capillary height; Plaster; Stone;

Wetting by simple room-temperature polymer melts: deviations from Newtonian behavior by G.K. Seevaratnam; L.M. Walker; E. Ramé; S. Garoff (265-270).
The hydrodynamics near moving contact lines of two room-temperature polymer melts, polyisobutylene (PIB) and polystyrene (PS), are different from those of a third polymer melt, polydimethylsiloxane (PDMS). While all three fluids exhibit Newtonian behavior in rotational rheological measurements, a model of the hydrodynamics near moving contact lines which assumes Newtonian behavior of the fluid accurately describes the interface shape of a variety of PDMS fluids but fails to describe the interface deformation by viscous forces in PIB and PS. The magnitude of the deviations from the model and the distance along the liquid–vapor interface over which they are seen increase with increasing capillary number. We conclude that the wetting behaviors of PIB and PS are influenced by weak elasticity in these low molecular weight melts and that dynamic wetting is more sensitive to this elasticity than standard rheometric techniques.
Keywords: Non-Newtonian; Polymer melts; Dynamic wetting; Contact angle;

The swelling clays have been proposed as engineered barriers in geological disposal systems for waste because these materials are assumed to build a better impermeable zone around wastes by swelling. However, the swelling potential of soils is also considered a prevalent cause of damage to buildings and constructions. For these reasons, it is fundamental to investigate the physicochemical and mechanical behavior of swelling clays. In the current study, the swelling–shrinkage potential (aggregates scale) was estimated using an environmental scanning electron microscope (ESEM) coupled with a digital image analysis (DIA) program (Visilog). In fact, the isolated aggregates of raw and cation-exchanged bentonite were directly observed at different relative humidities in an ESEM chamber. Then the “Visilog” software was used to estimate the percent augmentation of the aggregate surface as a function of time and as a function of relative humidity. This estimation allows for the calculation of the swelling–shrinkage potential (%) of bentonite. Finally, a kinetic model of first order was tested to fit the kinetic experimental data of swelling–shrinkage potential. The results show that ESEM–DIA coupling can be a powerful method of estimating the swelling–shrinkage potential of expansive clays. In addition, the exponential models fit well with the kinetic experimental data.
Keywords: Swelling–shrinkage; Kinetic; Bentonite; ESEM; Interlayer cations; Digital image analysis (DIA);

Hygroscopic growth of self-assembled layered surfactant molecules at the interface between air and organic salts by Yongsoon Shin; Li-Qiong Wang; Glen E. Fryxell; Greg J. Exarhos (278-281).
We report here the self-assembly of surfactant molecules at the interface of air and the hygroscopic quaternary ammonium salt tetrabutylammonium acetate (TBAAc). Homogeneously dissolved surfactant molecules at 100 °C self-assemble upon contacting air due to high moisture adsorption by the organic salt when cooling down. Highly ordered lamellar phases with different lattice spacings have been observed when surfactants with various lengths of alkyl chains were used. C n TMAB/TBAAc systems showed all-trans conformation of interior methylene carbons and interdigited bilayers with an average CH2 increment of 0.119 nm, while C n NH2/TBAAc systems showed trans/gauche mixed conformations of interior methylene carbons and bilayers with an average CH2 increment of 0.247 nm. C n NH2s in C n NH2/TBAAc formed bilayers through water-mediated intermolecular hydrogen bonds with a water layer thickness of 0.51–0.61 nm. In C n TAB/TBAAc, as the head group of C n TAB is bigger, the interdigited bilayer thickness (d-spacing) is smaller, because the bigger head groups accommodate enough space for alkyl tails to come in between them.
Keywords: Hygroscopic; Self-assembly; Surfactant; Interface; Lamellar;

The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization ( β ave ), minimum area per molecule of surfactant at the air–water interface ( A min ), surface excess concentration ( Γ max ), and Gibb's free energy of micellization ( Δ G mic ) of the surfactants were determined from conductance and surface tension data. The aggregation numbers (N), dimensions of micelles ( b / a ), effective fractional charge per monomer (α), and hydration of micelles ( h E ) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, β ave , and Δ G mic and an increase in N and b / a . This is well supported by the observed increase in hydration ( h E ) of micelles with increase in aggregation number (N) and dimension ( b / a ) of micelle.
Keywords: Gemini surfactant; SANS; Hydration of micelle; Head group polarity; Spacer length;

Due to complete proton transfer from the acid to the amine, a reaction between an equimolar mixture of dodecylamine and (meth)acrylic acid leads to the formation of dodecylammonium (meth)acrylate. The latter can be considered as a surfactant with a polymerizable organic counterion. The ternary phase diagrams of the two systems dodecylamine/acrylic acid/water and dodecylamine/methacrylic acid/water are described. Both systems can form isotropic solutions and lyotropic liquid crystalline lamellar phases. Moreover, the system with the methacrylate counterion can also form a cubic phase in the water-rich part of the phase diagram. The difference in the self-organization observed for the two systems is explained by the greater bulkiness and hydrophobicity of the methacrylate. Whereas the acrylate counterion behaves rather like a classic inorganic counterion, the methacrylate counterion resides in the outermost part of the aggregates, giving rise to a change in the surface curvature.
Keywords: Ternary phase diagram; Surfactant; Surfmer; 2H NMR; Self-assembly; Dodecylammonium; Acrylate; Methacrylate; Organic counterion;

Mixing behavior of fluorinated and hydrogenated gemini surfactants at the air–water interface by Jin Nishida; Aurélie Brizard; Bernard Desbat; Reiko Oda (298-305).
Mixing behavior of hydrogenated and fluorinated cationic gemini surfactants was studied at the air–water interface by Brewster angle microscopy and πA isotherm curves. In the bulk, these two molecules did not mix and showed phase separation. At the air–water interface, if a monolayer was formed by separate deposition of the two solutions, they formed separate domains, and the compression occurred in two steps: first the domains with hydrogenated gemini surfactant were compressed until they showed collapse; then the domains with fluorinated gemini surfactant were compressed. If the two solutions were mixed before the deposition, they remained mixed upon compression; on the other hand, separate domains under separate deposition were shown to mix if the subphase was heated.
Keywords: Fluorinated surfactant; Brewster angle microscope; Mixing behavior of monolayer; Air–water interface;

Two-fluid electroosmotic flow in microchannels by Yandong Gao; Teck Neng Wong; Chun Yang; Kim Tiow Ooi (306-314).
This paper presents a mathematical model to describe a two-fluid electroosmotic pumping technique, in which an electrically non-conducting fluid is delivered by the interfacial viscous force of a conducting fluid; the latter is driven by electroosmosis. The electrical potential in the conducting fluid and the analytical solution of the steady two-fluid electroosmotic stratified flow in a rectangular microchannel was presented by assuming a planar interface between the two immiscible fluids. The effects of viscosity ratio, holdup, concentration, and interfacial zeta potential are analyzed to show the potential feasibility of this technique.
Keywords: Two-fluid stratified flow; Electrical double layer; Electroosmotic pump;

The motivation of the study performed in this project is focused on deriving a more effective, accurate, and mathematically friendly solution for the prediction of the electrostatic potential, commonly used on electrokinetic research and its related applications. In this contribution, based on the Debye–Hückel approximation, a new solution strategy for the differential equations of the electrostatic potential is proposed. In fact, a simple predictor–corrector calculation is developed to achieve more accurate predictions of electrostatic potential profiles. Furthermore, in this study the authors introduce the correction function f AO to the inverse Debye length, λ. The f AO function improves the Debye–Hückel approximation and it is a recursive function of the electrical potential. Once the inverse Debye length, λ, has been corrected by the f AO function and introduced in the simplified solution of the Poisson–Boltzmann equation (i.e., the linear approximation, due to Debye and Hückel), the electrostatic potential outcome little differs from the numerical solution of the complete (nonlinear) differential equation. This new approach embraces different geometries of interest, such as planar, cylindrical, and annular, with excellent results in all the cases and for a wide range of electrostatic potential values. This new predicting semi-analytical technique can be a useful tool on electrical field applications such as the separation of a mixture of macromolecules and the removal of contaminants in soil cleaning processes. Illustrative results are presented for the geometries identified above.
Keywords: Poisson–Boltzmann; Electrostatics; Electrokinetics; Microfluidics; Soil remediation;

A new method was developed for analyzing the normal motion of a single colloidal particle near an interface. The optical technique of total internal reflection microscopy (TIRM) was used to determine the distribution of vertical displacements of a particle from a specific starting position as a function of time. At very small displacement times, the displacements are normally distributed with a variance that is proportional to the diffusion coefficient times the displacement time. The change in the diffusion coefficient with separation distance between the particle and plate was found to match that predicted by Brenner (Chem. Eng. Sci. 16 (1961) 242). As the sampling time becomes very large, the variance reaches a constant value determined strictly by the shape of the local potential energy profile holding the particle. A major advantage of this approach, relative to other measurement methods, is that the particle's spatially variant diffusion coefficient can be determined without any knowledge of the forces acting on the particle.
Keywords: Hindered mobility; Brownian motion; Total internal reflection microscopy;

Drag of a dispersion of nonhomogeneously structured flocs in a flow field by Jyh-Ping Hsu; Ming-Che Li; Audrey Chingzu Chang (332-338).
The influence of floc structure and floc concentration on the drag acting on a floc is investigated theoretically. A two-layer model is adopted to describe floc structure, and a cell model is used to simulate a floc dispersion. The influences of the key parameters of the problem under consideration, including floc concentration, Reynolds number, the ratio (permeability of outer layer/permeability of inner layer), and the ratio (thickness of outer layer/thickness of inner layer), on the drag coefficient are discussed. We show that the more heterogeneous the floc structure is, the greater the drag and the more significant the deviation of curve of variation of drag coefficient against Reynolds number from a Stokes-law-like relation. The drag on a floc declines with the decrease in floc concentration, and, due to the convective flow of the fluid, the distortion of streamlines surrounding a floc becomes more serious and the deviation of the variation of the curve of drag against Reynolds number from a Stokes-law-like relation is more significant.
Keywords: Floc dispersion; Cell model; Nonuniform floc structure; Two-layer model; Drag coefficient;

Thermophoresis in liquids is studied by molecular dynamics simulation (MD). A theory is developed that divides the problem in the way consistent with the characteristic scales. MD is then conducted to obtain the solution of each problem, which is to be all combined for macroscopic predictions. It is shown that when the temperature gradient is applied to the nonconducting liquid bath that contains neutral particles, there occurs a pressure gradient tangential to the particle surface at the particle–liquid interface. This may induce the flow in the interfacial region and eventually the particle to move. This applies to the material system that interacts through van der Waals forces and may be a general source of the thermophoresis phenomenon in liquids. The particle velocity is linearly proportional to the temperature gradient. And, in a large part of the given temperature range, the particle motion is in the direction toward the cold end and decreases with respect to the temperature. It is also shown that the particle velocity decreases or even reverses its sign in the lowest limit of the temperature range or with a particle of relatively weak molecular interactions with the liquid. The characteristics of the phenomenon are analyzed in molecular details.
Keywords: Thermophoresis; Neutral particle; Nonconducting liquid; Molecular dynamics simulation;

Temperature-induced sedimentation to dispersion of ionic vesicles by Hideya Kawasaki; Masahiko Miyahara; Mats Almgren; Göran Karlsson; Hiroshi Maeda (349-353).
We present a temperature-induced sedimentation/dispersion transition of ionic vesicles in the system of alkyldimethylamine oxide hemihydrochloride (CnDMAO ⋅ 1 2 HCl) with a hydrocarbon chain length of 12–16 ( n = 12 , 14, and 16) and sodium 2-naphthalenesulfonate (NaNphS). The temperature-sensitive sedimentation/dispersion of ionic vesicles took place around a temperature of 50 °C, which was weakly dependent on the alkyl chain length. The combined effect of the thermally induced dissociation of the counterions from the vesicle and a hydrogen bonding between the nonionic and the cationic head groups is likely to be responsible for this unique behavior.
Keywords: Dispersion of vesicles; Amine oxide; Temperature;

A novel nanogold multilayer constructed by Langmuir–Blodgett and self-assembly techniques by Xuehua Zhou; Chunyan Liu; Zhiying Zhang; Long Jiang; Jinru Li (354-357).
A multilayer comprising nanogold particles and organic molecules was constructed by self-assembly of the small organic molecule 1-phenyl-5-mercaptotetrazole onto the octadecylamine-protected nanogold monolayer in the course of transferring the monolayer, layer by layer, from a Langmuir–Blodgett trough to solid substrates. The structure and properties of the constructed multilayer were characterized by TEM images and ATR-IR, XPS, and UV–vis spectra. It is evidenced for the first time that the combination of Langmuir–Blodgett and self-assembly techniques provides a new way to organize functional nanoparticles such as organic–nanogold complexes.
Keywords: Nanogold multilayer; Langmuir–Blodgett and self-assembly techniques;

Enzymes in the cavity of hollow silica nanoparticles by Rakesh Kumar Sharma; Shraboni Das; Amarnath Maitra (358-361).
Due to limitations of the existing preparative methods of hollow nanoparticles by either heating at high temperature (>600 °C) or by using strong acid, alkali, or an organic solvent, it was not possible up till now to encapsulate any sensitive organic molecule like enzyme or others inside the cavity of hollow nanoparticles. We have demonstrated a much softer method of preparing hollow silica nanoparticles with horseradish peroxidase (HRP) inside the cavity by synthesizing HRP-doped core-shell silica-coated silver chloride nanoparticles and finally leaching out silver chloride with dilute ammonia at low temperatures. TEM pictures showed the hollow cavity inside the nanoparticles. The enzyme entrapped in these particles was active. The turnover number of HRP entrapped into these hollow particles and dispersed in aqueous buffer (pH 7.2) ( k cat = 2.56 × 10 6   s −1 ) was found to be less than that of free enzyme in aqueous buffer ( k cat = 6.133 × 10 7   s −1 ) but higher than that of HRP entrapped in solid-core silica nanoparticles and dispersed in aqueous buffer ( k cat = 1.05 × 10 5   s −1 ). The result showed that hollow nanoparticles could be prepared using soft chemical methods and sensitive chemicals like active enzyme could be entrapped in the cavities and it retains its activity.
Keywords: Hollow silica nanoparticles; HRP-doped hollow particles; Enzymatic activity;