Journal of Colloid And Interface Science (v.320, #2)
Long-term and thermally stable superhydrophobic surfaces of carbon nanofibers
by Nü Wang; Jinming Xi; Shutao Wang; Huan Liu; Lin Feng; Lei Jiang (pp. 365-368).
Carbon nanofibers were prepared from polyvinyl alcohol (PVA) by a simple wetting-compatible method. The surfaces of the aligned carbon nanofibers show excellent thermal- and time-stable superhydrophobicity. The average water contact angle (CA) values are about153.1±2.2° at room temperature, with little difference coming from experimental error. In addition, the CA of the aligned carbon nanofibers surface maintains139.1±3.2° after 10 months of exposure to the ambient environment. Nanostructure on the surface of carbon nanofibers and the intrinsic thermal resistance of carbon contribute to this unique surface property.Carbon nanofibers were prepared by a simple wetting-compatible method and show excellent thermal- and time-stable superhydrophobicity.
Keywords: Hydrophobicity; Carbon nanofibers; Nanostructures; Surface chemistry; Wettability
Uptake and effect of mercury on amino acid losses from the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis
by Marcos A. Cheney; Deborah Keil; Shizhi Qian (pp. 369-375).
Inorganic mercury (Hg2+) and herbicides are important contaminants of world water systems with effects on aquatic organisms and humans. The uptake of Hg2+ and glycine by the gills of the bivalve mollusks Mytilus californianus and Anodonta californiensis was determined. Additionally, the effects of glycine, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4-dinitrophenol (DNP) on the uptake of Hg2+ were also determined. The loss of primary amines from the excised gills of both species was measured in the presence and absence of Hg2+ or MeHg+. The results indicate that (1) the uptake of Hg2+ is approximately equivalent in both species; (2) comparison of the uptakes with that of inulin, which occupies only extracellular space, shows that Hg2+ is taken up; (3) the uptake of Hg2+ is slightly altered by the presence of glycine and herbicides such as 2,4-D and DNP; (4) the rate of loss of primary amines was highly increased relative to the control by the presence of Hg2+ and to a lesser extent MeHg+ for both species. These results showed that both inorganic and MeHg+ are effective in disrupting the permeability of cell membranes, causing leakage of essential amino acids from the cell. This could result in discharge of potential gradients, reduced efficiency of energy coupling, and consequently cell death.The uptake of Hg2+ by gill membranes and the effects of MeHg+ were determined. The obtained results showed that both inorganic and MeHg+ are effective in disrupting the permeability of cell membranes, causing leakage of essential amino acids from the cell.
Keywords: Mercury; Uptake; Amino acid; Losses; Membrane; Permeability
Synthesis, characterization, and sorption properties of silica gel-immobilized Schiff base derivative
by İ. Hilal Gübbük; Ramazan Güp; Mustafa Ersöz (pp. 376-382).
Silica gel was derivatized with benzophenone 4-aminobenzoylhydrazone (BAH), a Schiff base derivative, after silanization of silica by 3-chloropropyltrimethoxysilane (CPTS) by using a reported method. Characterization of the surface modification was confirmed through infrared spectroscopy, thermogravimetry, and elemental analysis. The immobilized surface was used for Cu(II), Ni(II), Zn(II), and Co(II) sorption from aqueous solutions. The influence of the amount of sorbent, ion concentration, pH, and temperature was investigated. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The mean sorption energy ( E) of benzophenone 4-aminobenzoylhydrazone (BAH) immobilization onto silica gel was calculated from D–R isotherms, indicating a chemical sorption mode for four cations. Thermodynamic parameters, i.e., Δ G, Δ S, and Δ H, were also calculated for the system. From these parameters, Δ H values were found to be endothermic: 27.0, 22.7, 32.6, and 34.6 kJ mol−1 for Cu(II), Ni(II), Co(II), and Zn(II) metal ions, respectively. Δ S values were calculated to be positive for the sorption of the same sequence of divalent cations onto sorbent. Negative Δ G values indicated that the sorption process for these three metal ions onto immobilized silica gel is spontaneous.Immobilized silica gel surface was used for Cu(II), Co(II), Zn(II), and Ni(II) sorption from aqueous solutions. The data were fitted to Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The thermodynamic parameters were calculated.
Keywords: Silica gel; Immobilization; Schiff base; Isotherm; Thermodynamics
Arsenic speciation in multiple metal environments: I. Bulk-XAFS spectroscopy of model and mixed compounds
by Markus Gräfe; Ryan V. Tappero; Matthew A. Marcus; Donald L. Sparks (pp. 383-399).
X-ray absorption fine structure (XAFS) spectroscopy was employed to determine the bonding environment of As(V) in the presence of Cu(II) and Zn(II) on goethite and gibbsite. In addition, several mineral species and precipitates derived from homogeneous and heterogeneous (presence of α-Cr2O3) super-saturations were studied. Structural parameters were determined after resolving the broad second shells in r-space by differential k-weighting (1, 2 or 3) and k-ranging (2.5- vs 3.5–12.75 Å) of the raw EXAFS functions. In precipitates, AsO4 was incorporated in the metal-hydroxides forming clinoclase-like and koettigite-like structures in the presence of Cu(II) and Zn(II), respectively. In the presence of both Cu(II) and Zn(II), the clinoclase structure formed preferentially over the koettigite structure under homogeneous oversaturated solution conditions and in the presence of eskolaite ( α-Cr2O3). Silica promoted the formation of koettigite-like zinc-arsenate precipitates from initial As(V) and Zn(II) solution concentrations of 500 μM. On goethite and gibbsite, 750 μM As(V) formed mainly bidentate binuclear surface species in accordance with many previous findings even in the presence of equimolar Cu(II) and or Zn(II) concentrations. Copper was readily identified in the second shell environment of As(V) sorbed on gibbsite, but not on goethite. We hypothesize that this complex formed on the basis of Cu(II)'s ability to form polymeric species in solution and at the mineral–water interface in agreement with previous studies. The effects of Zn(II) on the coordination environment of As(V) on gibbsite and goethite could not be ascertained with As K-edge EXAFS spectroscopy. In addition to bidentate binuclear surface complexes, As(V) formed edge-sharing complexes with Fe, Al, and Cu atoms, which we could differentiate on the basis of the inter-atomic distances, phase shifts between wavefunctions of Fourier-filtered peaks, and differences in amplitude of the absorption envelopes. The analyses showed that of all data reduction steps, data presented in r-space and as wavefunctions of Fourier-filtered shells offer the greatest possibility for fingerprinting and inferring the influence of co-sorbing metal cations on the As(V) sorption complex. With regards to interpretations of micro-EXAFS data by abstract factor analyses and linear least-square combination fitting, analyses of As K-edge data should not be performed on the rawχ(k) data, but rather on consistently isolated second and higher-order shell features.
Keywords: Copper; Zinc; Goethite; Gibbsite; EXAFS spectroscopy; Phase shifts; Edge-sharing complexes
Multi-competitive interaction of As(III) and As(V) oxyanions with Ca2+, Mg2+, PO3−4, and CO2−3 ions on goethite
by Monika Stachowicz; Tjisse Hiemstra; Willem H. van Riemsdijk (pp. 400-414).
Complex systems, simulating natural conditions like in groundwater, have rarely been studied, since measuring and in particular, modeling of such systems is very challenging. In this paper, the adsorption of the oxyanions of As(III) and As(V) on goethite has been studied in presence of various inorganic macro-elements (Mg2+, Ca2+, PO3−4, CO2−3). We have used ‘single-,’ ‘dual-,’ and ‘triple-ion’ systems. The presence of Ca2+ and Mg2+ has no significant effect on As(III) oxyanion (arsenite) adsorption in the pH range relevant for natural groundwater (pH 5–9). In contrast, both Ca2+ and Mg2+ promote the adsorption of PO3−4. A similar (electrostatic) effect is expected for the Ca2+ and Mg2+ interaction with As(V) oxyanions (arsenate). Phosphate is a major competitor for arsenate as well as arsenite. Although carbonate may act as competitor for both types of As oxyanions, the presence of significant concentrations of phosphate makes the interaction of (bi)carbonate insignificant. The data have been modeled with the charge distribution (CD) model in combination with the extended Stern model option. In the modeling, independently calculated CD values were used for the oxyanions. The CD values for these complexes have been obtained from a bond valence interpretation of MO/DFT (molecular orbital/density functional theory) optimized geometries. The affinity constants (logK) have been found by calibrating the model on data from ‘single-ion’ systems. The parameters are used to predict the ion adsorption behavior in the multi-component systems. The thus calibrated model is able to predict successfully the ion concentrations in the mixed 2- and 3-component systems as a function of pH and loading. From a practical perspective, data as well as calculations show the dominance of phosphate in regulating the As concentrations. Arsenite (As(OH)3) is often less strongly bound than arsenate (AsO3−4) but arsenite responses less strongly to changes in the phosphate concentration compared to arsenate, i.e.,δlogcAs(III)/δlogc(PO4)≈0.4 andδlogcAs(V)/δlogc(PO4)≈0.9 at pH 7. Therefore, the response of As in a sediment on a change in redox conditions will be variable and will depend on the phosphate concentration level.The CD model, calibrated on single ion systems, is able to predict the dominant role of phosphate on the As(III) and As(V) oxyanion concentrations in As–PO3−4–CO2−3–Ca2+–Mg2+ goethite systems.
Keywords: Goethite; Ferrihydrite; Iron oxide; Hydrous ferric oxide; Hematite; Bangladesh; Groundwater; Arsenic; Arsenate; Arsenite; Magnesium; Calcium; Phosphate; Bicarbonate; CD model; MUSIC model
Comparative simulation study of nitrogen and ammonia adsorption on graphitized and nongraphitized carbon blacks
by L.F. Herrera; D.D. Do; G.R. Birkett (pp. 415-422).
Grand canonical Monte Carlo simulation is used to study the adsorption of nitrogen at 77 K and ammonia at 240 K to represent weakly polar and polar molecules, respectively, on infinite and finite graphite surfaces. These graphite surfaces were modeled with different percentages of carbons removed (defects) from the top graphite layer. Increasing the number of defects increases the adsorption and the isosteric heat of nitrogen at low pressure. At moderate pressures the amount adsorbed is less due to the disruption in the packing of the nitrogen in the first layer. In contrast, the adsorption of ammonia at all pressures is reduced as the percentage of defects is increased. This is due to the disruption in ammonia bonding caused by the defects. The condensation-like step change in the ammonia isotherm on the perfect graphite surface is not observed for any of these surfaces with defects even for the case of only 10% defects. At high percentage of defects the adsorption isotherm is close to Henry law behavior for much of the pressure range. The adsorption on finite surfaces shows that the amount adsorbed for both molecules decreases compared with that of the infinite surfaces, resulting from interaction potentials with the surface and other fluid molecules at the edge. The decrease is much greater for the ammonia adsorption because the bonding between ammonia molecules is disrupted, meaning that the adsorption cannot follow the mechanism of condensation seen for the infinite surface.The local density distributions show the disruption to the packing of nitrogen caused by the defective surface, the effect on the ammonia adsorption is to disrupt the two-dimensional bonding and decrease the amount adsorbed.
Keywords: Molecular simulation; Nitrogen; Ammonia; Carbon black
Ammonia, cyclohexane, nitrogen and water adsorption capacities of an activated carbon impregnated with increasing amounts of ZnCl2, and designed to chemisorb gaseous NH3 from an air stream
by H. Fortier; P. Westreich; S. Selig; C. Zelenietz; J.R. Dahn (pp. 423-435).
The adsorption capacity of ZnCl2-impregnated activated carbon (AC) for NH3 is reported in terms of stoichiometric ratio of reaction (NH3 per ZnCl2). This ratio depends on the testing conditions used. Compared to the ratio obtained under dry conditions, the ratio is higher under humid conditions or increased NH3 concentrations. The linear increase of the NH3 capacity with increasing loading of ZnCl2 breaks down at about 3.5 mmol ZnCl2/g AC. This behavior is explained in terms of preferential adsorption of a monolayer of salt followed by aggregation of the impregnant once a monolayer is completed. The effect of increasing the loading of ZnCl2 on the capacity for gases for which the impregnants are not intended, namely cyclohexane, nitrogen, and water vapor, is also discussed. A break in the linear relationship between water capacity and impregnant loading at about 3.5 mmol ZnCl2 seems to correspond to a full monolayer coverage of ZnCl2 on AC. The monolayer of ZnCl2 is shown to reduce the uptake of water into AC, while the ZnCl2 aggregates are shown to be hydrophilic.ZnCl2 impregnated onto activated carbon forms a monolayer on the surface, followed by agglomeration into particles when the monolayer is complete.
Keywords: Impregnant; ZnCl; 2; monolayer; Hydrophilic aggregates; Gaseous adsorption; Chemisorption; Physisorption; Stoichiometric ratio of reaction; BET surface area; Pore size distribution; Adsorption kinetics
Preparation and applications of a variety of fluoroalkyl end-capped oligomer/hydroxyapatite composites
by Hiroki Takashima; Ken-ichi Iwaki; Rika Furukuwa; Katsuhisa Takishita; Hideo Sawada (pp. 436-444).
A variety of fluoroalkyl end-capped oligomers were applied to the preparation of fluorinated oligomer/hydroxyapatite (HAp) composites (particle size: 38–356 nm), which exhibit a good dispersibility in water and traditional organic solvents. These fluoroalkyl end-capped oligomer/HAp composites were easily prepared by the reactions of disodium hydrogen phosphate and calcium chloride in the presence of self-assembled molecular aggregates formed by fluoroalkyl end-capped oligomers in aqueous solutions. In these fluorinated HAp composites thus obtained, fluoroalkyl end-capped acrylic acid oligomers and 2-methacryloyloxyethanesulfonic acid oligomer/HAp nanocomposites afforded transparent colorless solutions toward water; however, fluoroalkyl end-cappedN,N-dimethylacrylamide oligomer and acryloylmorpholine oligomer were found to afford transparent colorless solutions with trace amounts of white-colored HAp precipitants under similar conditions. HAp could be encapsulated more effectively into fluorinated 2-methacryloyloxyethanesulfonic acid oligomeric aggregate cores to afford colloidal stable fluorinated oligomer/HAp composites, compared to that of fluorinated acrylic acid oligomers. These fluorinated oligomer/HAp composites were applied to the surface modification of glass and PVA to exhibit a good oleophobicity imparted by fluorine. HAp formation was newly observed on the modified polyethylene terephthalate film surface treated with fluorinated 2-methacryloyloxyethanesulfonic acid oligomers and acrylic acid oligomer/HAp composites by soaking these films into the simulated body fluid.RF-oligomer/HAp composites were applied to the surface modification of glass and PVA. In addition, HAp formation was observed on the modified polyethylene terephthalate film surface treated with RF-oligomers/HAp composites by soaking these films into the simulated body fluid.
Keywords: Fluorinated oligomer; Hydroxyapatite; Composites; Dispersibility; Surface modification; XRD; TEM; SEM; EDX; Simulated body fluid (SBF)
Self-assembly of polymer and molybdenum oxide into lamellar hybrid materials
by Ke Shao; Shangping Liao; Haimei Luo; Mingliang Wang (pp. 445-451).
We report on self-assembly of polymer and molybdenum oxide chains into a new class of lamellar hybrid materials. Aqueous ammonium molybdate and polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC) were used as the starting materials. Ammonium molybdate was hydrolyzed into layered molybdenum oxide under acidified conditions. The organic polymer chains and the inorganic molybdenum oxide layers self-assemble and pack into new hybrid composites. Scanning electron microscope (SEM) images and polarized microscopy show that these two new materials have typical lamellar structure. Transmission electron microscope (TEM) images show that the layer thickness is about 100 nm. X-ray diffraction (XRD) data confirm the formation of inorganic molybdenum oxide. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) data gave thermal behavior of these composites. The mechanism of this hybrid reaction and the templating function of polymers were discussed in this paper. A special entropy effect was discovered when polymer was used as guest species. This entropy effect makes polymers preferential candidates as guest species rather than small molecules when fabricating organic/inorganic layered hybrid materials. We believe that this opens a new way to create organic/inorganic hybrid superstructures.There exist two different reactions on both sides of these molybdenum oxide layers: packing into thicker molybdenum oxide layers on the one side and formation of hybrid on the other side.
Keywords: Layered material; Organic/inorganic hybrid; Molybdenum oxide
Influence of a hydrophobic diol on the micellar transitions of Pluronic P85 in aqueous solution
by B. Bharatiya; V.K. Aswal; P.A. Hassan; P. Bahadur (pp. 452-459).
Micellization behavior of an amphiphilic ethylene oxide–propylene oxide–ethylene oxide tri-block copolymer Pluronic P85 [(EO)26(PO)39–(EO)26] in aqueous solution and in the presence of a hydrophobic C14diol (also known as Surfynol®104) was examined by physico-chemical methods such as viscometry, cloud point (CP) and scattering techniques viz. dynamic light scattering (DLS) and small angle neutron scattering (SANS). The addition of diol decreases the cloud point and gelation temperature of aqueous Pluronic P85 copolymer solution. DLS and SANS measurements of the polymer in aqueous solution indicated micellar growth and sphere to rod transition in the presence of diol. Surfynol®104 is a sparingly water soluble diol surfactant with a solubility of ∼0.1 wt%. However, up on addition to Pluronic solution, diol gets incorporated in the block copolymer micelles and leads to structural transition of the micelles. An increase in the temperature and the presence of added sodium chloride in the solution further enhances this effect. The addition of hydrophobic C14diol increases the hydrodynamic size and aggregation numbers of the micellar system. The micellar parameters for the copolymer in the presence of C14diol are reported at different temperatures and added sodium chloride concentrations.SANS data for 5% P85 in water and NaCl with diol as additive: (□) 0 M NaCl + 0.0% diol, (●) 1 M NaCl + 0.0% diol, (▴) 1 M NaCl + 0.6% diol and (■) 1 M NaCl + 1% diol.
Keywords: Micellar transition; Aggregation number; Gelation
Polymer-associated liposomes as a novel delivery system for cyclodextrin-bound drugs
by Hyung Jun Lim; Eun Chul Cho; Jongwon Shim; Do-Hoon Kim; Eun Jung An; Junoh Kim (pp. 460-468).
It is known that cyclodextrins (CDs) extract lipid components from bilayer of liposomes. This could undermine the potential benefits of liposomes as drug carriers. In this study, we demonstrated that PC-Chol liposomes with various CDs or rhapontin (Rh)–hydroxypropyl βCD (HP βCD) complexes could be stabilized by association with the amphiphilic polyelectrolyte, poly(methacrylic acid- co-stearyl methacrylate). Based on the results of differential scanning calorimetry, photocorrelation spectroscopy and transmission electron microscopy, the polymer-associated liposomes had the same vesicular form as liposome with clear boundaries and retained structural integrity for at least 1 month. In addition, the polymer-associated structure was unaffected by the type of CD, the composition and concentration of lipid components, and the concentration of the Rh-HP βCD complex. This contrasted with PC-Chol liposomes, whose structure was dependent on these factors. Using structurally different polymer-associated liposomes and PC-Chol liposomes containing the Rh-HP βCD complex, we also showed that the stability of vesicles could influence the skin permeability of CD-drug complexes.Association of amphiphilic polyelectrolytes to liposome helps stabilize the vesicle in the presence of cyclodextrin–drug conjugates.
Keywords: Cyclodextrins; Liposomes; Polymer-associated liposome; Vesicles; Phosphatidylcholine
Modification of membrane heterogeneity by antipsychotic drugs: An X-ray diffraction comparative study
by Cedric Tessier; Philippe Nuss; Galya Staneva; Claude Wolf (pp. 469-475).
Lipid mixtures are used to mimic biological membranes as they allow characterization of lipid lateral domains defined by their specific lipid molecular organization. Therapeutic agents such as antipsychotic drugs (AP) that may interact with lipids arrangement are likely to modify membrane biological properties. The present study describes the effect of 2 typical and 5 atypical antipsychotic drugs on an aqueous co-dispersion of a lipid mixture made of egg phosphatidylcholine (PC)/brain sphingomyelin (SM)/cholesterol (1/1/1 mol/mol/mol). Lamellar liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence was identified in the control and antipsychotic-added mixtures at 37 °C using synchrotron small-angle X-ray scattering methods (XRD). Intensity of the Bragg peaks was used to generate electron density profiles (EDP) allowing bilayer thickness calculation. All antipsychotic except from amisulpride induced a Lo phase bilayer thickness (dpp) decrease. Chlorpromazine, haloperidol, amisulpride and 9-0H-risperidone induced a Lddpp increase while ziprazidone, risperidone and clozapine induced a Lddpp decrease, indicating that antipsychotic atypicality is not associated with a specificdpp modification on our lipid model mixture. Results are discussed in terms of competition of antipsychotic compounds with cholesterol and mode of reorganization of lateral domains. A pharmacological relevance of these changes is also discussed.Phospholipid bilayer arrangement of a mixture made of phosphatidylcholine/sphingomyelin and cholesterol in equimolar proportion. All antipsychotic drugs decreased Lo phase bilayer thickness; their effect on the Ld phase differed depending on the studied compound.
Keywords: X-ray diffraction; SAXS; Electron density profile; Phospholipid bilayers; Sphingomyelin; Phosphatidylcholine; Cholesterol; Antipsychotic; Liquid-ordered phase; Liquid-disordered phase
Rat osseous plate alkaline phosphatase as Langmuir monolayer—An infrared study at the air–water interface
by Luciano Caseli; Douglas C. Masui; Rosa P.M. Furriel; Francisco A. Leone; Maria E.D. Zaniquelli; Jhony Orbulescu; Roger M. Leblanc (pp. 476-482).
A glycosylphosphatidylinositol (GPI)-anchored enzyme (rat osseous plate alkaline phosphatase—OAP) was studied as monolayer (pure and mixed with lipids) at the air–water interface. Surface pressure and surface potential–area isotherms showed that the enzyme forms a stable monolayer and exhibits a liquid-expanded state even at surface pressure as high as 30 mN m−1. Isotherms for mixed dimyristoylphosphatidic acid (DMPA)–OAP monolayer showed the absence of a liquid-expanded/liquid-condensed phase transition as observed for pure DMPA monolayer. In both cases, pure or mixed monolayer, the enzyme preserves its native conformation under compression at the air–water interface as observed from in situ p-polarized light Fourier transform-infrared reflection–absorption spectroscopic (FT-IRRAS) measurements. Changes in orientation and conformation of the enzyme due to the presence or absence of DMPA, as well as due to the surface compression, are discussed.Alkaline phosphatase adsorbed on phospholipid monolayers at the air–water interface: characterization by infrared spectroscopy.
Keywords: Alkaline phosphatase; Langmuir monolayers; Air–water interface; Infrared
Filtration method characterizing the reversibility of colloidal fouling layers at a membrane surface: Analysis through critical flux and osmotic pressure
by Benjamin Espinasse; Patrice Bacchin; Pierre Aimar (pp. 483-490).
A filtration procedure was developed to measure the reversibility of fouling during cross-flow filtration based on the square wave of applied pressure. The principle of this method, the apparatus required, and the associated mathematical relationships are detailed. This method allows for differentiating the reversible accumulation of matter on, and the irreversible fouling of, a membrane surface. Distinguishing these two forms of attachment to a membrane surface provides a means by which the critical flux may be determined. To validate this method, experiments were performed with a latex suspension at different degrees of destabilization (obtained by the addition of salt to the suspension) and at different cross-flow velocities. The dependence of the critical flux on these conditions is discussed and analysed through the osmotic pressure of the colloidal dispersion.
Keywords: Critical flux; Ultrafiltration; Colloids; Membrane; Irreversibility; Fouling; Osmotic pressure
Synthesis and characterization of one-dimensional CdSe by a novel reverse micelle assisted hydrothermal method
by Lifei Xi; Yeng Ming Lam; Yan Ping Xu; Lain-Jong Li (pp. 491-500).
Nanocrystalline cadmium selenide (CdSe) is a low bandgap material (Eg=1.75eV, at room temperature) with potential applications in photoelectronic devices. Its electronic properties are dependent on the dimensions of the crystals. In this study, one-dimensional wurtzite CdSe nanoparticles with a diameter of43±6nm and an aspect ratio of3.7±0.6 were synthesized through a novel reverse micelle assisted hydrothermal method at a relatively low temperature. This method combines the advantages of the hydrothermal method's ability to achieve good crystallinity with the well-controlled growth offered by the reverse micelle method. The morphology of the nanoparticles can be controlled by the amount of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), the amount of hydrazine hydrate and the reaction temperature. It is proposed that AOT controls the length while hydrazine hydrate controls the diameter of the growing nanocrystals. The photoluminescence (PL) of individual nanorods and the longitudinal-optical phonon properties were mapped using confocal microscopy. Raman spectroscopy showed a blue-shift of both the LO and 2LO phonon peaks which may be due to a lattice contraction of the CdSe nanorods. A nucleation and growth mechanism for these nanoparticles is also proposed based on time-dependent studies.UV–vis absorption (a) spectrum, PL spectra of 35 dots (b) and the confocal microscopic image (c) of as-prepared CdSe nanorods.
Keywords: Reverse micelles; Hydrothermal method; Nanoparticles; Surfactants
Preparation and characterization of hydrophobic TiO2 pillared clay: The effect of acid hydrolysis catalyst and doped Pt amount on photocatalytic activity
by Xuejun Ding; Taicheng An; Guiying Li; Shanqing Zhang; Jiaxin Chen; Jianmei Yuan; Huijun Zhao; Hui Chen; Guoying Sheng; Jiamo Fu (pp. 501-507).
Titanium hydrate sols were prepared using different acid hydrolysis catalysts, i.e., acetic acid and hydrochloric acid. The platinum-doped TiO2 sol–gels were also synthesized by adding K2PtCl6 into the titanium hydrate sols. The hydrophobic montmorillonite clay, treated with organic cationic surfactant, i.e., hexadecyltrimethylammonium bromide, was used as a template to prepare TiO2 pillared photocatalyst with the above sols. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX) were employed to characterize the resulting photocatalysts. The adsorption performance and photoactivity of prepared pillared clays were studied by using methyl orange as a model organic pollutant. The preliminary results indicated that the hydrophobic TiO2 pillared clay prepared with acetic acid as the acid hydrolysis catalysts possessed higher photocatalytic activity than that with hydrochloric acid. Due to the excellent sedimentation property of the clay, the resulting pillared photocatalyst is easily recovered and reused in the postrun treatment. Also the doping of platinum into the hydrophobic photocatalyst can increase the photocatalytic activity significantly.The adsorption capacity and photocatalytic activity of pillared MCHA and MCHCL clays are increased significantly, when compared with the original MC clay.
Keywords: Pillared clay; Photocatalyst; Platinum; Preparation; Characterization
Ennoblement of stainless steel in the presence of glucose oxidase: Nature and role of interfacial processes
by J. Landoulsi; M.J. Genet; C. Richard; K. El Kirat; P.G. Rouxhet; S. Pulvin (pp. 508-519).
The ennoblement of the free corrosion potential (Ecorr) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H2O2). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H2O2 medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Feox/Crox and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Feox/Crox ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H2O2, in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H2O2 through the change of surface composition. TheEcorr ennoblement seems to be directly due to the presence of H2O2 and to the electrochemical behavior of H2O2 and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H2O2 through the change of surface composition but to a direct electrochemical effect of H2O2.
Keywords: Biocorrosion; Stainless steel; Passive film; XPS; AFM; Glucose oxidase; H; 2; O; 2; Iron oxides; Organic contamination
Influence of magnesia modification on the properties of copper oxide supported on γ-alumina
by Zhe Wang; Haiqin Wan; Bin Liu; Xi Zhao; Xiaowei Li; Haiyang Zhu; Xuan Xu; Fangying Ji; Keqin Sun; Lin Dong; Yi Chen (pp. 520-526).
XRD, BET, TPR, UV–vis DRS and in situ FT-IR were employed to investigate the dispersion, reduction and CO2-adsorption behaviors of copper oxide supported on magnesia modified γ-Al2O3 (Mg–Al) samples. The results indicate that magnesia could be highly dispersed on the surface of γ-Al2O3 to form a monolayer and the dispersion capacity is about 1.55 mmol/(100 m2 γ-Al2O3). For copper oxide supported on Mg–Al samples, both the dispersion capacity and the reduction temperature of surface CuO decrease with the MgO loading. CO2-adsorption IR results show that the surface strong basic amount for the catalysts increases with the dispersed MgO loading. In addition, the activity of CO oxidation suggests that the main active species in this system should be small CuO cluster and the existence of dispersed MgO enhances the activity of CO oxidation. The catalysts might be applied in pollution control devices for vehicle exhaust, CO gas sensors, catalytic combustion and gas purification of CO2 lasers. All the results have been discussed by the consideration of the variation of γ-Al2O3 surface structure before and after magnesia modification.In current experimental conditions, magnesia might preferentially incorporate into the surface octahedral vacant sites of γ-Al2O3. The properties of the catalysts (CuO/ γ-Al2O3) are closely related to the magnesia loading amount.
Keywords: Copper oxide; Magnesia; Dispersion capacity; “CO + O; 2; ” reaction
Investigation of the properties of organically modified ordered mesoporous silica films
by Sang-Bae Jung; Tae-Jung Ha; Hyung-Ho Park (pp. 527-534).
Organically modified, ordered mesoporous silica films, which can provide hydrophobicity and low polarizability to the framework, were prepared using Brij-76 block copolymer as a template. Due to a fast condensation reaction of the silica precursor, mesostructured silica films were not properly synthesized. To circumvent this problem, a synthesis procedure was modified to provide an enhancement of pore periodicity through the incorporation of methyl ligands on the framework. The micropore volume was reduced, and the pore size was enlarged, as the concentration of the methyl ligands on the framework was increased. A mesophase transition from a two-dimensional hexagonal structure to a body-centered cubic (BCC) structure was observed according to the concentration of incorporated methyl ligands. The mechanical properties of the fabricated films were investigated according to the pore ordering and film density. The mechanical properties of the films with random pore geometry show a positive correlation between film density and elastic modulus. Meanwhile, the mechanical behavior of organically modified mesoporous silica films with periodic pore distribution represents a negative correlation within a certain density range, which is advantageous to the low- k materials. Especially, film with a low micropore volume fraction and BCC pore ordering is more applicable to a low- k material due to low dielectric constant and high mechanical strength.A mesophase transition from a two-dimensional hexagonal structure to a body-centered cubic (BCC) structure according to the concentration of incorporated methyl ligands.
Keywords: Ordered mesoporous silica film; Organic modification; Brij-76; Micropore; Mechanical properties; Low-; k
Removal and regeneration of aqueous divalent cations by boehmite
by Shigeru Sugiyama; Yuki Kanda; Hisaaki Ishizuka; Ken-Ichiro Sotowa (pp. 535-539).
Boehmite (Al(OH)O) was employed for the removal of aqueous Mg2+, Cu2+, Cd2+, Pb2+, and Co2+ at 298 K. Although boehmite was able to remove these divalent cations, the greater removal rate with boehmite of Pb2+ (28.7%) than with Mg2+, Cu2+, Cd2+, and Co2+ (5.6, 25.3, 10.9, and 13.3%, respectively) was observed under acidic conditions. Under stronger alkaline conditions, in which the lead species was completely dissolved, a greater removal rate of Pb2+ (more than 80%) was observed under the corresponding conditions employed for the acidic conditions. The removed lead species could not be dissolved from boehmite in an acidic solution while an evident dissolution of lead species was detected using an aqueous NaOH solution. The results shown in the present study reveal that boehmite can be employed as a reagent for the removal and regeneration of aqueous metal cations.Removal of aqueous divalent cations with boehmite was possible while that of Pb2+ proceeded favorably. Lead removed on boehmite could be regenerated with alkaline treatment.
Keywords: Boehmite; Removal and regeneration; Aqueous divalent cations
Fabrication of CdS films with superhydrophobicity by the microwave assisted chemical bath deposition
by Y. Liu; T. Tan; B. Wang; R. Zhai; X. Song; E. Li; H. Wang; H. Yan (pp. 540-547).
A simple method of microwave assisted chemical bath deposition (MA-CBD) was adopted to fabricate cadmium sulfide (CdS) thin films. The superhydrophobic surface with a water contact angle (CA) of 151° was obtained. Via a scanning electron microscopy (SEM) observation, the film was proved having a porous micro/nano-binary structure which can change the property of the surface and highly enhance the hydrophobicity of the film. A possible mechanism was suggested to describe the growth of the porous structure, in which the microwave heating takes an important role in the formation of two distinct characteristic dimensions of CdS precipitates, the growth of CdS sheets in micro-scale and sphere particles in nano-scale. The superhydrophobic films may provide novel platforms for photovoltaic, sensor, microfluidic and other device applications.
Keywords: PACS; 81.15.-z; 68.08.BcWettability; Cadmium sulfide films; Micro-nano-binary structures; Microwave irradiation; Superhydrophobic
Dicyanopyrazine-linked porphyrin Langmuir–Blodgett films
by Sung Taek Kang; Heejoon Ahn (pp. 548-554).
We investigated the influence of arachidic acid/cadmium dication (AA/Cd2+) as a transfer promoter for the deposition of dicyanopyrazine-linked porphyrin (2-DCPP) Langmuir–Blodgett (LB) films on both hydrophobic and hydrophilic substrates. In the case of LB deposition on a hydrophilic substrate, the presence of AA/Cd2+ does not improve 2-DCPP LB deposition. The poor transfer in the case of the hydrophilic surface is believed to be due to 2-DCPP not wetting the surface during the down-stroke deposition, and this is not improved by the transfer agent. However, on a hydrophobic substrate, deposition of 2-DCPP is significantly improved by the presence of AA/Cd2+. Comparison of the UV–visible spectrum of a 2-DCPP LB film with that of 2-DCCP dissolved in chloroform reveals that the Soret and Q bands for the 2-DCPP LB film are broadened and red-shifted due to aggregation of porphyrin rings in the LB film. UV–visible spectral changes and ellipsometry as a function of the number of deposition layers suggest continuous transfer of 2-DCPP/AA onto the hydrophobic substrate and reproducibility in the deposition process. The Soret and Q bands of the 2-DCPP LB film upon acid vapor exposure have also been investigated, and these measurements may have chemical sensor applications.
Keywords: Acid vapor sensing; Dicyanopyrazine; Langmuir–Blodgett films; Porphyrin
Solid–liquid interfacial energy of neopentylglycol
by Y. Ocak; S. Akbulut; K. Keşlioğlu; N. Maraşlı (pp. 555-562).
The grain boundary groove shapes for equilibrated solid neopentylglycol (2,2-dimethyl-1,3-propanediol) (NPG) with its melt were directly observed by using a horizontal temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient ( Γ), solid–liquid interfacial energy (σSL), and grain boundary energy (σgb) of NPG have been determined to be(7.4±0.7)×10−8Km,(7.9±1.2)×10−3Jm−2, and(15.4±2.5)×10−3Jm−2, respectively. The ratio of thermal conductivity of equilibrated liquid phase to solid phase for the NPG has also been measured to be 1.07 at the melting temperature.The Gibbs–Thomson coefficient, solid–liquid interfacial energy, and grain boundary energy of neopentylglycol were determined. Thermal conductivity ratio of liquid phase to solid phase for neopentylglycol was also measured.
Keywords: Organic materials; Crystal growth; Interfacial energy; Grain boundary energy; Thermal conductivity ratio
Inferring wettability of heterogeneous surfaces by ToF-SIMS
by Craig Priest; Nathanael Stevens; Rossen Sedev; William Skinner; John Ralston (pp. 563-568).
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been examined as a possible predictive tool for surface wettability. Heterogeneous surfaces were prepared with hydrophilic and hydrophobic regions of known surface coverage using self-assembled monolayers. The surface coverage of each component was then correlated with ToF-SIMS fragmentation of the hydrophobic and hydrophilic surface groups and static contact angle measurements. From these measurements, a clear relationship between the surface wettability and relative intensity of characteristic secondary ions was identified. Moreover, our results for planar surfaces can be extrapolated to predict the wettability of particulate samples for which direct contact angle measurements are not straightforward. The ability to infer particle wettability by ToF-SIMS is well suited to mineral characterization and in particular, the prediction of mineral flotation efficiencies.The wettability of chemically heterogeneous particles and plates, such as this incomplete octadecylphosphonic acid monolayer on mica, can be inferred from time-of-flight secondary ion mass spectroscopy.
Keywords: Wetting; ToF-SIMS; Contact angle; Heterogeneity
Droplet structure instability in concentrated emulsions
by Yasushi Saiki; Roger G. Horn; Clive A. Prestidge (pp. 569-574).
Dynamic rheological measurements are reported on concentrated emulsions of monodispersed sodium dodecyl sulfate-stabilized polydimethylsiloxane droplets with different cross-linking levels (i.e., controllable deformability and either viscous or viscoelastic) and over a volume fraction range 0.5 to 0.72. Emulsion structure instability is revealed at a volume fraction of 0.7 and is represented by an anomalously lowG′/G″ crossover stain,γco (G′, elastic modulus;G″, viscous modulus). This phenomenon is independent of the droplet cross-linking level and not observable for hard-sphere silica sols of volume fractions from 0.54 to 0.63. It is suggested that the structural instability arises from deformation-induced formation of “slip planes” between droplet layers specific to the repulsive droplets at the specific volume fraction, which may be dependent on the droplet packing configurations for the given polydispersity of the system. Theγco value may be considered as an in situ index of the structural stability and interdroplet interaction balance in concentrated emulsions.Dynamic rheological studies on concentrated emulsions of monodispersed PDMS droplets have identified specific regions of droplet structural instability.
Keywords: Polydimethylsiloxane; Emulsions; Dynamic rheology; Droplet deformability; Packing configuration
Rheological behavior of thermoreversible κ-carrageenan/nanosilica gels
by A.L. Daniel-da-Silva; F. Pinto; J.A. Lopes-da-Silva; T. Trindade; B.J. Goodfellow; A.M. Gil (pp. 575-581).
The rheological behavior of silica/ κ-carrageenan nanocomposites has been investigated as a function of silica particle size and load. The addition of silica nanoparticles was observed to invariably impair the gelation process, as viewed by the reduction of gel strength and decrease of gelation and melting temperatures. This weakening effect is seen, for the lowest particle size, to become slightly more marked as silica concentration (or load) is increased and at the lowest load as particle size is increased. These results suggest that, under these conditions, the particles act as physical barriers to polysaccharide chain aggregation and, hence, gelation. However, for larger particle sizes and higher loads, gel strength does not weaken with size or concentration but, rather, becomes relatively stronger for intermediate particles sizes, or remains unchanged for the largest particles, as a function of load. This indicates that larger particles in higher number do not seem to increasingly disrupt the gel, as expected, but rather promote the formation of stable gel network of intermediate strength. The possibility of this being caused by the larger negative surface charge found for the larger particles is discussed. This may impede further approximation of neighboring particles thus leaving enough inter-particle space for gel formation, taking advantage of a high local polysaccharide concentration due to the higher total space occupied by large particles at higher loads.The addition of silica nanoparticles impairs the gelation process, as viewed by the reduction of gel strength and decrease of gelation and melting temperatures.
Keywords: Carrageenan; Silica; Rheology thermoreversible gel; Gel transition; Nanocomposite
Electrokinetic flow of non-Newtonian fluids in microchannels
by Claudio L.A. Berli; María L. Olivares (pp. 582-589).
A theoretical description of the electrokinetic flow of non-Newtonian fluids through slit and cylindrical microchannels is presented. Calculations are based on constitutive models of the fluid viscosity, and take into account wall depletion effects of colloids and polymer solutions. The resulting equations allow one to predict the flow rate and electric current as functions of the simultaneously applied electric potential and pressure gradients. It is found that (i) nonlinear effects induced by the shear-dependent viscosity are limited to the pressure-driven component of the flow, and (ii) the reciprocity between electroosmosis and streaming current is complied. Thus a generalized form of the force–flux relations is proposed, which is of interest in microfluidic applications.Electroosmotically induced flow of a complex fluid (gray, power law; white, Newtonian) in a slit microchannel, for different values of a simultaneously applied counterpressure.
Keywords: Electrokinetic flow; Non-Newtonian fluids; Nonlinear Onsager relations; Microfluidics
Molecular-scale model for the mass density of electrolyte solutions bound by clay surfaces: Application to bentonites
by J. Gonçalvès; P. Rousseau-Gueutin (pp. 590-598).
A model to simulate the density of solutions adsorbed onto clay mineral surfaces is proposed. In this model, the alteration of the ionic distribution caused by the electric field associated with the surface charge of clay platelets is accounted for using an electrical triple-layer model with an overlapping diffuse layer. The combined effects of ion hydration and the electric field on the structure of water are introduced through their influence on the partial molar volume of water. This model, applied to Na-montmorillonite, simulates the distribution of the interplatelet solution density as a function of the distance to the mineral surface. High densities in the direct vicinity of the surface and slightly lower density (a few percent) than the normal density in the diffuse layer are obtained. These results show good consistency with the available data on bentonite and with the densities that can be inferred from molecular dynamics simulations. This model shows that the interplatelet distance plays an important role in the distribution of the mass density of the solution in the pore space of clay rocks.Calculated density for a Na-montmorillonite with an equilibrium solution concentrationCf=10−3molL−1 and an interplatelet half-distance r of 7 nm. MD stands for molecular dynamics simulation and data* for reconstructed profile using the data of Fig. 1 (see text).
Keywords: Electrical model; Ions hydration; Electrostriction; Mass density
Electric double layer and electrostatic interaction of hydrophobic particles
by N. Mishchuk (pp. 599-607).
An hypothesis regarding the impact of water density near hydrophobic surfaces on the electrostatic component of their interaction was offered. A theoretical model of the electric double layer and the interparticle interaction under conditions of the variable density and, consequently, variable dielectric permittivity of water has been developed. It was shown that reduction of the dielectric permittivity near interfaces determined by their hydrophobicity resulted in compression of double electrical layers and weakening of their overlapping. This, in its turn, results in reduction of the electrostatic repulsion of hydrophobic disperse particles as compared with nonhydrophobic ones.Developed theoretical model of interparticle interaction shows strong dependence of the electrostatic repulsion energyU/U0 on the change of dielectric permittivity at the thin layer of water near a hydrophobic surfaceε1/ε.
Keywords: Dielectric permittivity; Density of water; Hydrophobicity; Electric double layer; Repulsion
Spontaneous vesicles of sodium dihexadecylphosphate in HEPES buffer
by Eloi Feitosa (pp. 608-610).
The formation of spontaneous vesicles of dihexadecylphosphate (DHP) in a HEPES buffered solution at pH 7.4, the size, morphology and melting temperature, obtained by cryogenic transmission electron microscopy (cryo-TEM) and differential scanning calorimetry (DSC), are reported. The vesicles were formed by simply mixing a 5.0 mM lipid–solvent mixture at a temperature (75 °C) safely above the higher melting temperatureTm=70.4 °C of DHP. The vesicle diameter ranges from 100 to 332 nm and their geometry is spherical, faceted or oblong.Tm increases from 66.8 to 70.4 as DHP concentration is raised from 0.6 to 5.0 mM.Cryo-TEM image of the spontaneous DHP vesicles in HEPES buffer (bar = 100 nm).
Keywords: DHP vesicle; Spontaneous vesicle; Differential scanning calorimetry; Cryo-TEM
Dynamic interaction between oppositely charged vesicles: Aggregation, lipid mixing, and disaggregation
by Daisuke Saeki; Shinji Sugiura; Teruhiko Baba; Toshiyuki Kanamori; Seigo Sato; Sukekuni Mukataka; Sosaku Ichikawa (pp. 611-614).
We investigated dynamic interactions between oppositely charged small unilamellar vesicles using positively charged vesicles containing 1,2-dioleoyl-3-trimethylammonium-propane or 3 β-[ N-(N′,N′-dimethylaminoethane)-carbamoyl] cholesterol and negatively charged vesicles containing L- α-phosphatidyl-DL-glycerol. Aggregation, lipid bilayer mixing, contents mixing and contents leakage were systematically examined using optical density measurements, fluorescence resonance energy transfer assays, fluorescence quenching assays, light-scattering analyses, and freeze-fracture transmission electron microscopy. The oppositely charged vesicles aggregated immediately. Lipid mixing was observed, but there was no mixing of the contents. The vesicle aggregates disaggregated spontaneously after several minutes. The surface potential of the disaggregated vesicles was neutralized. From these results, we infer that the lipids in the external monolayers were exchanged between the oppositely charged vesicles while the internal monolayers remained intact. The two types of cationic lipids used exhibited different speeds of disaggregation.Mixing positively charged PC/DOTAP (70/30 molar ratio) vesicles with negatively charged PC/PG (70/30) vesicles induced rapid aggregation followed by spontaneous disaggregation after several minutes.
Keywords: Vesicle; Charged lipid; Aggregation; Lipid mixing; Lipid exchange; Disaggregation; Fusion