Journal of Colloid And Interface Science (v.323, #1)

The adsorption of DPKSH onto Amberlite XAD-2 (styrene resin) and XAD-7 (acrylic ester resin) has been investigated, at ( 25 ± 1 ) ° C and pH 4.7. The experimental equilibrium data were fitted to the Langmuir, Freundlich, and Dubinin–Radushkevich (D-R) models. These three models provide a very good fit for both resins and the respective constants K L , K F , and K DR were calculated. For the same DPKSH concentration interval, the minimum time of contact for adsorption maximum at XAD-7 was smaller than at XAD-2 and the maximum amount of DPKSH adsorbed per gram of XAD-2 is smaller than at XAD-7. The investigation indicates that the mean sorption energy (E) characterizes a physical adsorption and the surfaces of both resins are energetically heterogeneous. The constants obtained in these studied systems were correlated and compared with those obtained for the silica gel/DPKSH system.The adsorption of DPKSH onto Amberlite XAD-2 and XAD-7 was investigated, at 25 °C and pH 4.7. The equilibrium data were fitted to the Langmuir, Freundlich, and Dubinin–Radushkevich models.
Keywords: Adsorption; DPKSH; XAD-7; XAD-2; Isotherms;

Structural features of polymer adsorbent LiChrolut EN and interfacial behavior of water and water/organic mixtures by V.M. Gun'ko; V.V. Turov; V.I. Zarko; Y.M. Nychiporuk; E.V. Goncharuk; E.M. Pakhlov; G.R. Yurchenko; T.V. Kulik; B.B. Palyanytsya; T.V. Borodavka; T.V. Krupskaya; R. Leboda; J. Skubiszewska-Zięba; V.D. Osovskii; Y.G. Ptushinskii; A.V. Turov (6-17).
The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1H NMR spectroscopy with layer-by-layer freezing-out of liquids (190–273 K), and thermally stimulated depolarization current method (90–265 K). This adsorbent is characterized by large specific surface area (∼1500 m2/g) and pore volume (0.83 cm3/g) with a major contribution of narrow pores ( R < 10 nm ) of a complicated shape (long hysteresis loop is in nitrogen adsorption–desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1H NMR data.Structural features of polymer adsorbent LiChrolut EN differently influence the behavior of water and water/organic mixtures confined in micropores and mesopores.
Keywords: Porous polymer adsorbents; Carbon adsorbents; Adsorption; TEM; SEM; FTIR; TPD MS; NMR; TSDC;

Spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) have been used to investigate the adsorption of a mouse monoclonal antibody (type IgG1, anti-β-hCG) on hydrophilic silica (bearing weak negative charges above pH 3), followed by the assessment of binding of human chorionic gonadotrophin (hCG). The antibody is a relatively large molecule with a molecular weight of 150 kDa and the isoelectric point (IP) around pH 6. The antibody adsorption was conducted at pH 4.0, 6.0 and 8.0 to examine the role of charge interaction. Ellipsometric results show that away from the IP, both initial adsorption rate and surface excess decreased, with the reduction at pH 8.0 being more pronounced than that at pH 4.0 due to the electrostatic repulsion not only between the charged antibody molecules within the adsorbed layer but also between antibody and the silica surface. Whilst parallel AFM measurements confirmed the main trend of pH dependent antibody adsorption, they also revealed the tendency of surface aggregation with increasing surface coverage. AFM height profiling at low surface coverage confirmed the “flat-on” orientation of adsorbed antibody molecules, consistent with the previous study by neutron reflection. Interestingly, the antibody height at pH 4.0 was found to be lower than that at pH 8.0, showing the influence from different electrostatic interactions under the two pH conditions. Subsequent hCG binding to the adsorbed antibodies was found to decrease with increasing surface coverage due to the steric hindrance. Under similar antibody surface coverage, the hCG binding ratio at pH 8 was higher than that at pH 4.0, a difference that could only be accounted for by the tighter surface confinement at pH 4.0.Specific binding of antigen hCG to pre-adsorbed antibody anti-hCG (▵) compared to the control (○).
Keywords: Protein adsorption; Antibody adsorption; Biomolecules immobilization; Biointerface;

Benzene-1,3,5-tri-carboxylic acid (trimesic acid, TMA) coated on basic alumina has been shown to be an effective adsorbent for Fe(III) and Fe(II) from aqueous solution. A comparative study on the adsorption of Fe(III) and Fe(II) revealed that TMA coated alumina is more selective towards Fe(III) than Fe(II). The maximum adsorptions of Fe(III) and Fe(II) were 26.6 mg/g and 8.4 mg/g, respectively. Fe(III)/Fe(II) adsorption was also compared in some cases with adsorption of Co(II) and Ni(II). Maximum uptakes ( Q m ) for Co(II) and Ni(II) were found much lower (∼1 mg/g) than Fe(III)/Fe(II). pH dependent studies have revealed that Fe(III) was adsorbed efficiently at high acidic condition (pH ∼1.5) compared to Fe(II), Co(II) and Ni(II), while temperature did not have significant effect on the adsorption processes. Adsorption of Fe(III) and Fe(II) was quite rapid and thermodynamically favourable. Adsorption processes fitted well in Langmuir isotherm model and followed second order rate kinetics in all cases.Trimesic acid coated alumina is a potent and specific adsorbent for Fe(III) from aqueous solution in presence of Fe(II), Cu(II), Co(II) and Ni(II) ions.
Keywords: Trimesic acid; Basic alumina; Adsorption specificity; Adsorption isotherm kinetics; Competitive iron removal;

Surface complexation modeling of Sr(II) and Eu(III) adsorption onto oxidized multiwall carbon nanotubes by Changlun Chen; Jun Hu; Di Xu; Xiaoli Tan; Yuedong Meng; Xiangke Wang (33-41).
Acid–base titrations of oxidized multiwall carbon nanotubes (MWCNTs), Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs were conducted to investigate the surface charge characteristics of oxidized MWCNTs and the surface complexation interactions between Sr(II)/Eu(III) and oxidized MWCNTs. The results suggested that Sr(II) and Eu(III) adsorptions onto oxidized MWCNTs increased with increasing pH, and decreased with increasing ionic strength, and the affinity of oxidized MWCNTs for Eu(III) was much higher than that for Sr(II). The diffuse layer model (DLM) fitted the experimental data of Sr(II) and Eu(III) adsorptions well with the aid of FITEQL 3.2.Acid–base titrations of oxidized MWCNTs at three ionic strengths.
Keywords: Multiwall carbon nanotubes; Adsorption; Sr(II); Eu(III); Surface complexation;

Surface complexation modeling of uranium(VI) sorbed onto zirconium oxophosphate versus temperature: Thermodynamic and structural approaches by M.G. Almazan-Torres; R. Drot; F. Mercier-Bion; H. Catalette; C. Den Auwer; E. Simoni (42-51).
This work presents an investigation of the interaction mechanisms between uranyl ions and a solid phosphate, the zirconium oxophosphate: Zr2O(PO4)2. Both thermodynamic and structural points of view are developed. Indeed, prior to any simulation of the retention data, it is necessary to precisely characterize the system under study in order to gain information at a molecular scale. First, the intrinsic surface properties of this synthetic compound have been investigated for different temperatures ranging from 25 to 90 °C. Mass and potentiometric titrations show that the surface site density remains constant between 25 and 90 °C, while the experimental point of zero charge slightly decreases from 4.8 to 4.5 with an increasing temperature. The potentiometric titration data are simulated, for each temperature, using the constant capacitance model and taking into account two surface sites (Zr―O and P―O) with a total surface site density equal to 7.0 sites nm−2. For both reactive sites, the intrinsic protonation constants do not change with the temperature, while the deprotonation ones increase. These results led to the determination of the associated enthalpy and entropy changes according to the van't Hoff relation. Second, the speciation of U(VI) at the solid/solution interface has been studied using two complementary spectroscopic techniques probing the sorbed uranyl ions: time-resolved laser-induced fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (EXAFS). The substrate presents two different reactive surface sites against uranium retention, which are constituted by the oxygen atoms of the surface PO4 groups and the oxygen atoms linked to the zirconium atoms. Two inner-sphere complexes are thus present on the substrate, their relative proportion depending on the pH value of the suspension. The effects of the temperature (25–90 °C) on the surrounding uranium were checked using the TRLFS technique. The uranyl sorption constants onto the Zr2O(PO4)2 substrate were determined taking into account the structural investigation. The surface complexation modeling was performed using the constant capacitance model included in the FITEQLv4.0 code. The four adsorption edges obtained at 25, 50, 75, and 90 °C were simulated. The modeling of these experimental data was realized considering two surface complexes ((ZrOH)2UO2+ 2, (PO)2UO2) according to the structural investigation. The constant value associated with the ZrO site does not change with the temperature, while the one corresponding to the PO site increases. Finally, the enthalpy and entropy changes associated with the uranyl sorption constants have been determined using the van't Hoff relation.U(VI)/Zr2O(PO4)2 sorption edge modelling for temperature ranged between 25 and 90 °C was realized on the basis of structural investigations. Both enthalpy and entropy changes associated to these processes were evaluated.
Keywords: Surface properties; Zirconium oxophosphate; Temperature; Speciation; Uranyl; Modeling; Spectroscopy; Thermodynamic analysis;

Porogen effects in synthesis of uniform micrometer-sized poly(divinylbenzene) microspheres with high surface areas by Dong-xia Hao; Fang-ling Gong; Wei Wei; Guo-hua Hu; Guang-hui Ma; Zhi-guo Su (52-59).
A new method of synthesizing uniform poly(divinylbenzene) (polyDVB) microspheres with high specific surface areas was designed by combining Shirasu porous glass (SPG) membrane emulsification, suspension polymerization, and post-crosslinking techniques. It was shown that the physicochemical properties of porogens have a great influence on the size distribution and porous features of microspheres. The low aqueous solubility of porogen facilitated preparation of uniform emulsions and microspheres, and high aqueous solubility led to polydispersed emulsions and poor microsphere yields. Such aqueous solubility effects can be tailored by adding a low molecular weight polystyrene (LPST) as costabilizer in porogen, thus improving the uniformity of microspheres. Moreover, different affinities of porogens for copolymers demonstrate various contributions to specific surface areas of microspheres in suspension polymerization especially post-crosslinking. Solvating porogen requires a much higher addition than nonsolvating porogen to obtain equal specific surface areas in polymerization, but has more potential to enhance the specific surface area in post-crosslinking. Two kinds of uniform microspheres were obtained with high specific surface areas, up to 706.6 m2/g by heptane and 937.5 m2/g by toluene.Two kinds of uniform microspheres with high specific surface area were obtained, respectively up to 706.6 m2/g by heptane and 937.5 m2/g by toluene, which present different porous feature and adsorption modes.
Keywords: Poly(divinylbenzene); Uniform sized; High specific area; Membrane emulsification; Post-crosslinking;

The interaction between poly-l-lysine (pLys) and oppositely charged poly(acrylic acid) (pAA) microgels (Ø ∼ 80–120 μm) was studied by micromanipulator-assisted light microscopy and confocal laser scanning microscopy. The aim of this study was to investigate effects of peptide size, pH, and salt concentration on binding, transport, and distribution of pLys in pAA microgel particles and thereby also to outline the details of the gel deswelling in response to pLys binding and incorporation. Both peptide distribution and gel deswelling kinetics were found to be strongly influenced by the pLys molecular weight, originating partly from limited entry of large peptides into the gel particle core. Also pH was shown to influence both deswelling and pLys incorporation kinetics, with a decreased deswelling rate observed with increasing pH. These effects are determined by a complex interplay between the pH-dependence of both pLys and the gel network, also influencing volume transitions of the latter. Finally, salt concentration was shown to have a significant effect on both gel deswelling rate and pLys transport, with an increased electrolyte concentration resulting in decreased deswelling rate but also in an increased peptide transport rate within the microgel particles.pLys distribution in pAA microgels and the rate of microgel deswelling depend on the size of peptide.
Keywords: Confocal microscopy; Deswelling; Kinetics; Microgel; Peptide; Poly(acrylic acid); Poly-l-lysine;

DPPC incorporation into egg-PC unilamellar vesicles reduces their oxidation rate beyond that expected from the unsaturated lipid dilution. Addition of the unsaturated lipids produces changes in the physical properties of the inner parts of the lipid bilayer, as sensed by fluorescence anisotropy of DPH, and in the hydrophilic/hydrophobic region, as sensed by the generalized polarization of laurdan. DPPC (30 mol%) incorporation into egg-PC vesicles produces a decrease in alkyl chain mobility in the inner part of the bilayer, evaluated by the increase of DPH fluorescence anisotropy, and a rise of the generalized polarization value of laurdan in the bilayer interface. It also leads to a decrease in the rate of water efflux promoted by a hypertonic shock. Oxidation of PC LUVs, promoted by AAPH, as sensed by oxygen uptake and MDA formation, leads to qualitatively similar results than DPPC addition: rigidification at the inner part and the surface of the liposomes, and a lower rate of water permeation. It is suggested that these changes could contribute to the observed decrease in oxidation rate with conversion.The DPPC incorporation into egg-PC vesicles produces changes in the physical properties of the inner parts and in the hydrophilic/hydrophobic region of the lipid bilayer. The addition produces a decrease in alkyl chain mobility in the inner part of the bilayer and a decrease in the rate of water efflux promoted by a hypertonic shock. The same effect is produced when the oxidation of egg-PC LUVs is carried out, rigidification of the inner part and the surface of the liposomes, and a lower rate of water permeation.
Keywords: Lipid peroxidation; Egg-PC-DPPC vesicles; Water transport; Membrane rigidity;

Cationic agents for DNA compaction by Sylwia Gawęda; M. Carmen Morán; Alberto A.C.C. Pais; Rita S. Dias; Karin Schillén; Björn Lindman; M. Graça Miguel (75-83).
Fluorescence microscopy was used to investigate the conformational changes of individual T4 DNA molecules induced by different compacting agents, namely the cationic surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), iron(III), lysozyme, and protamine sulfate. A protocol for establishing size estimates is suggested to obtain reproducible results. Observations show that in the presence of lysozyme and protamine sulfate, DNA molecules exhibit a conformational change from an elongated coil structure to compact globules, usually interpreted as a first-order transition. The maximum degree of compaction that is attained when iron(III) or CTAB (CTAC) are used as compacting agents is considerably smaller, and intermediate structures (less elongated coils) are visible even for high concentrations of these agents. Dynamic light scattering experiments were carried out, for some of the systems, to assess the reliability of size estimates from fluorescence microscopy.Fluorescence microscopy is used to investigate the conformational changes of individual T4 DNA molecules induced by different compacting agents, namely the cationic surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), iron(III), lysozyme, and protamine sulfate. A protocol for establishing size estimates is suggested to obtain reproducible results. In the presence of proteins, DNA molecules exhibit a conformational change from an elongated coil structure to compact globules. The maximum degree of compaction that is attained with iron(III) or CTAB is considerably smaller, and intermediate structures are visible even for high concentrations of these agents.
Keywords: DNA compaction; Coexistence; Intermediate structures; Fluorescence microscopy; Dynamic light scattering;

Surface functionalized zirconia nanoparticles were prepared by covalent grafting of a methacrylate functionalized silane (methacryloxypropyltrimethoxysilane, MPTS) onto the surface of the zirconia nanoparticles (tetragonal and mixed monoclinic/tetragonal phase) obtained by hydrothermal treatment of zirconyl chloride octahydrate. The particles are 70 nm aggregates of nanometric primary grains (4–12 nm) with inter particle porosity. BET measurements show that the specific surface area of the particles after activation at 100 °C is between 85 and 204 m2/g depending on the mineralizer used (Sr2+, Ca2+, Mg2+). IR-measurements show that the surface of the particles can be covered with functional groups bound through a variable number of Zr―O―Si bonds to render them organocompatible. The surface modified particles were dispersed in monomer solution (butanediol monoacrylate, BDMA) and polymerized to form films by adding a cross linking agent (trimethylolpropane triacrylate, Laromer TMPTA) and an UV initiator (2,4,6-trimethylbenzoyldiphenylphosphine oxide, Lucirin TPO). The received films were characterized with thermogravimetry and UV–vis spectroscopy.Surface functionalized zirconia nanoparticles are integrated into highly transparent acrylate films by in situ UV-polymerization of stable monomer particle dispersions.
Keywords: Hydrothermal synthesis; ZrO2 nanocrystallites; MPTS, (MPS, MAPTS, MEMO) surface modification; UV cured acrylate films;

A simple numerical method, which does not involve numerical integration of the Poisson–Boltzmann equations, is presented for obtaining the relationship between the Donnan potential and surface potential of a spherical soft particle (i.e., a polyelectrolyte-coated particle) in a symmetrical electrolyte solution. We assume that a soft particle consists of the particle core of radius a covered with an ion-penetrable surface layer of polyelectrolytes of thickness d and that ionized groups of valence Z are distributed at a uniform density of N in the polyelectrolyte layer and the relative permittivity takes the same value in the regions outside and inside the polyelectrolyte layer. The Donnan potential and surface potential are determined by the values of a, d, Z, N, and the Debye–Hückel parameter κ of the electrolyte solution. Numerical results obtained by the present method are in excellent agreement with exact results obtained by solving the nonlinear spherical Poisson–Boltzmann equations for the both regions inside and outside the polyelectrolyte layer.Potential distribution across a polyelectrolyte layer.
Keywords: Donnan potential; Surface potential; Spherical soft particle;

Hexagonal mesoporous silica modified with copper phthalocyanine as a photocatalyst for pesticide 2,4-dichlorophenoxiacetic acid degradation by Edimar DeOliveira; Cláudio R. Neri; Anderson O. Ribeiro; Vinícius S. Garcia; Leonardo L. Costa; Aline O. Moura; Alexandre G.S. Prado; Osvaldo A. Serra; Yassuko Iamamoto (98-104).
A new mesoporous catalyst was prepared by the reaction between 3-aminopropyltrimethoxisylane and Cu(II)-hexadecafluorophthalocyanine, followed by co-condensation of tetraethylorthosilicate around a micelle formed by n-dodecylamine. The surfactant was removed from the pores by continuous extraction with ethanol, giving the Si–CuF16Pc catalyst. This catalyst was characterized by SEM, FTIR, TGA, 29Si NMR, N2 adsorption and X-ray diffraction. SEM images confirmed that the catalyst material is formed by nanoaggregates with a diameter of 100 nm. N2 adsorption isotherms showed that Si–CuF16Pc has a surface area of approximately 200 m2 g−1 and a porous diameter of 7.7 nm, characterizing the mesoporosity of this product. This novel material shows an excellent photocatalytic activity, degrading almost 90% of 2,4-dichlorophenoxyacetic acid (2,4-D) up to 30 min, while only approximately 40% of photodegradation was obtained in its absence.The mesoporous catalyst was prepared by Cu(II)-hexadecafluorophthalocyanine covalently bonded inside hexagonal mesoporous silica. This material shows excellent catalytic activity for the photodegradation of the 2,4-dichlorophenoxyacetic acid up to 30 min.
Keywords: Silica; Copper phthalocyanine; 2,4-Dichlorophenoxyacetic acid (2,4-D); Photodegradation;

Direct deposition of gold nanoparticles onto polymer beads and glucose oxidation with H2O2 by Tamao Ishida; Kyoko Kuroda; Naoto Kinoshita; Wataru Minagawa; Masatake Haruta (105-111).
Gold nanoparticles (Au NPs) were deposited directly from aqueous solution of diethylenediaminegold(III) complex onto polymer beads commercially available, such as poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyaniline (PANI) without surface modification. The dropwise addition of NaBH4 to reduce Au(III) was found to be very effective to obtain small Au(0) NPs with a narrow size distribution except for PANI. The catalytic performance of Au NPs deposited on polymer beads for H2O2 decomposition and glucose oxidation with H2O2 were more significantly affected by the kinds of polymer supports than by the size of Au NPs. The equimolar oxidation of glucose with H2O2 could be operated by controlling the decomposition rate of H2O2 over Au/PMMA.The choice of an Au precursor and the dropwise addition of a reductant yielded small Au NPs directly deposited onto polymers, which were active for glucose oxidation with H2O2.
Keywords: Gold nanoparticles; Catalysis; Polymer supports; H2O2 decomposition; Glucose oxidation;

Removal of natural organic matter by ultrafiltration with TiO2-coated membrane under UV irradiation by Arie Dipareza Syafei; Cheng-Fang Lin; Chung-Hsin Wu (112-119).
This study investigates the performance of ultrafiltration (UF) by membranes coated with titanium dioxide (TiO2) photocatalyst under ultraviolet (UV) illumination in removing natural organic matter (NOM) and possibly in reducing membrane fouling. Experiments were carried out using heat-resistant ceramic disc UF membranes and humic acids as model substances representing naturally occurring organic matter. Membrane sizes of 1, 15, and 50 kDa were used to examine the effects of coating under ultraviolet irradiation. A commercial humic solution was subjected to UF fractionation (batch process); gel filtration chromatography was applied to study the effects of molecular weight distribution of NOM on UF membrane fouling. When compared to naked membranes, UV254 (ultraviolet light of λ = 254   nm ) illumination of TiO2-coated membranes exhibits more flux decline with similar effluent quality. Although the UF membrane is able to remove a significant amount of humic materials, the incorporated photocatalysis results in poor performance in terms of permeate flux. The TiO2-coated membrane under UV254 irradiation alters the molecular weight (MW) distribution of humic materials, reducing them to <1 kDa, which is smaller than the smallest (1-kDa) membrane in this study. Thus, TiO2-coated membranes under UV254 irradiation do not perform any better in removing natural organic matter and reducing membrane fouling.With increased of attention towards ultrafiltration membranes in water treatment to remove natural organic matter, and it is aimed to examine the membrane performance by coating with TiO2. The effect of coating with TiO2 on membrane performance is examined. Figure: Scanning electron microscope microscopy of TiO2-coated membrane.
Keywords: Ultrafiltration; TiO2; Photocatalysis; Humic acid; Membrane fouling; Flux decline;

Preparation of hydrophilic/hydrophobic porous materials by Xuan Li; Chen Zhang; Zhongjie Du; Hangquan Li (120-125).
A novel porous material was designed and prepared in this work. A hydrophobic open-celled porous polystyrene (PS) was first synthesized via a concentrated emulsion polymerization of water in styrene. Subsequently the porous polystyrene was saturated with an aqueous solution of acrylamide (AM) and an initiator, which was subjected to another polymerization and the resulted polyacrylamide (PAM) penetrated in the cells and intercellular pores of the PS matrix. The PAM would change its volume according to the environmental humidity and thus adjusted the permeation of the material. The morphology, pore size distributions, water absorption, and vapor permeation of the materials were investigated.Novel porous PS/PAM composites were synthesized for the permeation behavior in different environmental humidity to adjust the cells open or closed.
Keywords: Concentrated emulsion; Porous material; Polystyrene; Polyacrylamide; Permeation;

Contact line mobility in liquid droplet spreading on rough surface by Limei Xu; Hui Fan; Chun Yang; Wei Min Huang (126-132).
We quantitatively estimate the effect of the substrate roughness on the liquid droplet spreading. Since the droplet size is in the order of millimeters, the surface energy becomes the dominant factor. A nonequilibrium thermodynamics framework [Y.X. Gao, H. Fan, Z. Xiao, Acta Mater. 48 (2000) 863–874] seems feasible for describing the millimeter size droplet spreading on a solid substrate. Within the framework, there are two system constants, namely the mobilities of liquid/air surface and the triple joint contact line that need to be determined from experimental testing. In the present paper, we demonstrate the experimental process of determining the mobility of the contact line via a droplet spreading on a steel substrate. Particularly, we obtained the contact line mobility on a steel surface with various roughness values. It is shown that the mobility value is lower for a rougher surface.The experimental data of Plate 1 with roughness of R a = 0.128   μm are fitted into a dimensionless numerical curve. The contact line mobility is calculated as M L = R ∗ t 0 γ LV .
Keywords: Wetting; Surface tension; Nonequilibrium thermodynamics;

Elasticity-driven droplet movement on a microbeam with gradient stiffness: A biomimetic self-propelling mechanism by Xiu-Peng Zheng; Hong-Ping Zhao; Ling-Tian Gao; Jian-Lin Liu; Shou-Wen Yu; Xi-Qiao Feng (133-140).
Directional movement of liquid droplets is of significance not only for certain physiological processes in nature but also for design of some microfluidic devices. In this study, we report a novel way to drive directional movement of liquid droplets on a microbeam with a varying or gradient stiffness. We use the energy method to theoretically analyze the interaction between a droplet and the elastic microbeam. The system tends to have the minimum potential energy when the droplet moves to the softer end of the beam. Therefore, a gradient change of the bending stiffness may be utilized to help the directional motion of droplets. Similarly, one can also drive droplets to move in a designed direction by varying the cross sectional geometry of the beam. Finally, some possible applications of this self-propelling mechanism are suggested.Energy method is used to analyze a droplet on a beam with varying stiffness. We found that the droplet may spontaneously move from the stiffer to the softer end.
Keywords: Surface tension; Substrate stiffness; Directional motion; Elasticity; Solid/liquid interface;

Aggregation and micellization of sodium dodecyl sulfate in the presence of Ce(III) at different temperatures: A conductometric study by Artur J.M. Valente; Hugh D. Burrows; Sandra M.A. Cruz; Rui F.P. Pereira; Ana C.F. Ribeiro; Victor M.M. Lobo (141-145).
Aggregation properties of sodium dodecyl sulfate (SDS) in the presence of cerium(III) chloride, at various temperatures (298.15–323.15 K) have been measured by the electrical conductance technique. The experimental data on aqueous solutions as a function of SDS concentration show the presence of two inflexion points indicating the presence of two distinct interaction mechanisms: the first, occurring at SDS concentrations below the critical micelle concentration of the pure surfactant, which can be explained by the formation of aggregates between dodecyl sulfate (DS) and Ce(III), while the second one, at SDS concentrations around the critical micelle concentration (cmc) of the pure surfactant which is due to the SDS micellization. The aggregation between DS and Ce(III) was confirmed by static light scattering. The binding ratio of DS/Ce(III) changes from 6 to 4, shows a slight dependence on the Ce(III) concentration and is independent of the temperature. The thermodynamic micellization parameters, Gibbs energy, enthalpy and entropy of micellization were calculated on the basis of the experimental data for the aggregation concentration, and the degree of counterion dissociation of the micelles. The SDS micellization is energetically favoured by increasing either the concentration of CeCl3 or the temperature. Such behaviour is clearly dominated by a decrease of the micellization (exothermic) enthalpy. The entropy of micellization approaches zero as the cerium(III) chloride concentration and temperature increase.At the SDS pre-micellar concentration aggregates of Ce(III)/dodecyl sulfate are formed; these aggregates have an influence on the SDS micellization. The SDS micellization is favoured by increasing either the concentration of Ce(III) or the temperature.
Keywords: Cerium(III); Sodium dodecyl sulfate; Lanthanides; Micellization parameters; Aggregation;

Excluded volume effect on the electrophoretic mobility of colloidal particles by J.J. López-García; M.J. Aranda-Rascón; J. Horno (146-152).
In a recent work [J. Colloid Interface Sci. 316 (2007) 196] we studied the influence of the excluded volume effect on spatial distributions of ionic species and electrostatic potential in the neighborhood of a suspended spherical particle. It was shown that the excluded volume effect considerably increases the surface potential (for a given value of the particle charge) as compared to the case when ideal ion behavior is assumed. In the present work we extend our previous equilibrium results to the perturbed/nonequilibrium problem and analyze the effect of ion size constraints on the electrophoretic mobility of a rigid spherical particle immersed in a general electrolyte solution. We find that the electrophoretic mobility always increases with the excluded volume effect, which might broaden the range of experimental data that can be interpreted, including those cases where the measured mobility exceeded the theoretical maximum value predicted by the standard model.The excluded volume effect ( c max ) always increases the electrophoretic mobility as compared to the case when ideal ion behavior is assumed (standard model). This fact extends the range of experimental data that can be interpreted, including those cases where the measured mobility exceeded the theoretical maximum value predicted by the standard model.
Keywords: Excluded volume effect; Finite ion size; Electrophoretic mobility;

Field induced rotational viscosity of ferrofluid: Effect of capillary size and magnetic field direction by Nidhi Andhariya; Bhupendra Chudasama; Rajesh Patel; R.V. Upadhyay; R.V. Mehta (153-157).
In the present investigation we report the effect of capillary diameter and the direction of applied magnetic field on the rotational viscosity of water and kerosene based ferrofluids. We found that changes in the field induced rotational viscosity are larger in the case of water based magnetic fluid than that of kerosene based fluid. The field induced rotational viscosity is found to be inversely proportional to the capillary diameter and it falls exponentially as a function of the angle between the direction of field and vorticity of flow. Magnetophoretic mobility and hydrodynamic volume fraction of nanomagnetic particles are determined for above cases.
Keywords: Rotational viscosity; Magnetic fluid; Magnetophoretic mobility;

We investigated the influences of the magnetic field strength and particle areal density on the microstructure of a quasi-two-dimensional monolayer composed of ferromagnetic particles by means of a Monte Carlo simulation. The magnetic field was applied along a direction perpendicular to the plane of the monolayer. Microstructures of the monolayer obtained in the simulations were analyzed in terms of radial distribution and orientational distribution functions. Formation of the microstructures is discussed from the perspective of particle–particle interaction energy and the perpendicular magnetic susceptibility of the monolayer was calculated from simulated magnetization curves. The obtained results are summarized as follows. For small areal density of particles, formation of chain-like structures is prevented by the repulsive magnetic interaction between particles due to orientations of the magnetic moments in the particles along the magnetic field direction. For intermediate areal density of particles, the chain-like structures remain even when a relatively strong magnetic field is applied, because contributions of the attractive magnetic interactions increase. For large areal density of particles, mixtures of chain-like and locally ordered structures appear due to the anisotropic attractive magnetic interactions in the absence of the magnetic field. However, when a sufficiently strong magnetic field is applied, the magnetic interactions between particles change to isotropic repulsive interactions, which results in the short-range repulsive steric interactions between particles becoming dominant with the appearance of hexagonal close packed structures.The microstructure of a monolayer composed of ferromagnetic particles in quasi-two-dimensional system exhibits a hexagonal close-packed structure in a very strong perpendicular magnetic field for the large areal density of particles.
Keywords: Ferromagnetic particles; Chain-like structures; Monolayer; External magnetic field; Monte Carlo simulations;

Synthesis of well-defined poly(N-isopropylacrylamide)-b-poly(L-glutamic acid) by a versatile approach and micellization by Lin Deng; Keyu Shi; Yuying Zhang; Haimei Wang; Jianguo Zeng; Xianzhi Guo; Zongjie Du; Baolong Zhang (169-175).
A novel Fmoc-protected chain transfer agent (CTA) was synthesized and applied in the reversible addition–fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAAm), resulting in well-defined Fmoc-protected PNIPAAm and the amino-end capped PNIPAAm by the subsequent hydrolysis. Poly(N-isopropylacrylamide)-b-poly(l-glutamic acid) (PNIPAAm-b-PLGA) with controlled molecular weight and narrow molecular weight distribution was synthesized successfully via ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs) by using PNIPAAm-NH2 as the macroinitiator. Both pH- and thermo-responsive micellization behaviors of the block copolymer PNIPAAm55-b-PLGA35 in dilute aqueous solution were investigated by means of the pyrene fluorescence, circular dichroism, 1H NMR, transmission electron microscopy and dynamic and static light scattering. Spherical PLGA-core and rod-like PNIPAAm-core micelles are formed in response to pH and temperature. The reversible transition between the PLGA-core and PNIPAAm-core micelles was observed. This work provides a versatile approach for synthesizing well-defined stimuli-responsive polypeptide-based double hydrophilic diblock copolymers (DHBCs), and is of great potential for generating useful stimuli-responsive materials in biomedical applications.Schematic representation of the micellization of PNIPAAm55-b-PLGA35 block copolymers in aqueous solution.
Keywords: pH-responsive; Thermo-responsive; Polypeptide-based block copolymer; Micellization;

In this paper, we constructed an ordered self-organized film possessing a well-defined layered structure by using a polymerizable surfactant-encapsulated polyoxometalloeuropate, (DMDA)9EuW10O36 (DMDA: dodecyl(11-methacryloyloxyundecyl)dimethylammonium bromide). The in situ polymerization of the film through UV irradiation was investigated by using 1H NMR and FTIR spectra, and X-ray diffraction. The results show that 68% of the monomers that connect to the complex in the film have been polymerized at the utmost. In contrast to the virgin layered structure of the casting film which possesses a layer spacing of 2.7 nm, the layer thickness increases to about 3.3 nm after the in situ polymerization. The lifetime and the quantum yield of the polyoxometalate in the casting film were found to increase due to the change of the layered structure after in situ polymerization. Thus, the present results provide an effective way to tune the photophysical properties of the film through alteration of the layered structure. In the meantime, the stability of the casting film in the alkaline solution was improved after in situ polymerization.A cross-linked hybrid film is constructed by solvent casting of a polymerizable surfactant-encapsulated polyoxometalate, followed by photo-induced polymerization, thus both photophysics and stability of the film are tuned and improved.
Keywords: Surfactant-encapsulated polyoxometalate; Casting film; In situ polymerization; Photophysical properties;

Preparation and photocatalytic properties of Fe3+-doped Ag@TiO2 core–shell nanoparticles by Wenjiao Wang; Jinlong Zhang; Feng Chen; Dannong He; Masakazu Anpo (182-186).
Ag@TiO2 core–shell-type nanophotocatalysts have been prepared using a simple and convenient method. The products were characterized by TEM, XRD, and UV–vis spectra. To make the catalysts achieve the highest photocatalytic activity under UV light illumination, the Ag content of Ag@TiO2 was optimized. The results showed that Ag@TiO2-doped Fe3+ extend their absorption into the visible region. Among the Fe3+-doped samples, Ag@Fe–TiO2 with low Ag content showed higher photocatalytic activity under visible light illumination. An excessive added amount of Ag would reduce Fe3+ to Fe2+ and make them difficult to be incorporated into the lattice of titania. From the experiments, we found that Fe3+ ions could stabilize the Ag@TiO2 colloid by holding back the aggregation of the core–shell nanoparticles.Acting as an electron trap, the Ag core is protected by a TiO2 shell from corrosion or dissolution. Fe3+ doped on the Ag@TiO2 system can enhance the photocatalytic activity under visible light illumination.
Keywords: Titanium dioxide; Photodegradation; Ag@TiO2; Fe3+ doping; Core–shell structure;

Pyramidal assemblies of colloidal particles by micromolding underneath top-gathering pillar arrays by Hiroyo Segawa; Yasuo Yamazaki; Shigeru Tachiki; Tetsuji Yano; Shuichi Shibata (187-190).
Assemblies of colloidal particles are known to have special photonic and optical properties. Periodic pyramidal assemblies of SiO2 particles with diameters of 0.5 and 1 μm were fabricated using top-gathering pillar arrays as a new template. These top-gathering pillar arrays consisted of four pillars gathered at the top, and were fabricated by photolithography of an organic–inorganic hybrid material. The top-gathering units were obtained by controlling both the capillary and restoring forces. When a colloidal water suspension was spread on the template and the water was allowed to evaporate, the SiO2 particles were molded under the top-gathering pillars according to particle size, resulting in pyramidal assembly arrays of the particles. From in situ observation during the evaporation of water, it was found that the particles were molded underneath the top-gathering pillars by flux generated by the evaporation and by the capillary force among the particles.Pyramidal assemblies of silica particles were obtained by micromolding in top-gathering pillar arrays, which were fabricated from organic–inorganic hybrid materials by the photolithography.
Keywords: Pyramidal assembly; Mold; Capillary force; Silica particles; Topgathering pillar array;

Interactions between cationic bottle-brush polyelectrolyte layers adsorbed on mica across salt and oppositely charged surfactant solutions were investigated with the interferometric surface force apparatus, and the results were compared with what is known for similarly charged linear polyelectrolytes. Ellipsometric measurements demonstrated that the bottle-brush polyelectrolytes, which contain 45 units long poly(ethylene oxide) side chains, are more readily desorbed than linear equivalents when the ionic strength of the solution is increased. It is argued that this is due to the steric repulsion between the poly(ethylene oxide) side chains that reduces the surface affinity. The preadsorbed bottle-brush polyelectrolyte layers were also exposed to sodium dodecyl sulfate (SDS) solutions. It was found that the presence of SDS affected the force profiles less than observed for similarly charged linear polyelectrolytes. This observation was attributed to excluded volume constraints imposed by the poly(ethylene oxide) side chains that reduces the accessibility of the charged polyelectrolyte segments and counteracts formation of large aggregates within the layer.The protective side-chains of bottle-brush polyelectrolytes increase the stability of the formed polymer layers, in solutions containing oppositely charged surfactants.
Keywords: Polyelectrolyte; Brush polyelectrolyte; Bottle-brush polyelectrolyte; Comb polyelectrolyte; Poly(ethylene oxide); Surfactant; Association; Surface force apparatus (SFA); Phase modulated ellipsometry; Mica; Sodium dodecyl sulfate;