Journal of Colloid And Interface Science (v.306, #1)
Editorial Board (CO1).
Comments on “A new mechanistic parachor model to predict dynamic interfacial tension and miscibility in multicomponent hydrocarbon systems” by S. Ayirala and D. Rao [J. Colloid Interface Sci. 299 (2006) 321–331] by F.M. Orr; K. Jessen (1-2).
This comment points out an error of interpretation of experimental results reported in [J. Colloid Interface Sci. 299 (2006) 321–331].
Keywords: Minimum miscibility pressure;
Adsorption of phthalic acid and salicylic acid and their effect on exchangeable Al capacity of variable-charge soils by Jiuyu Li; Renkou Xu (3-10).
Low-molecular-weight (LMW) organic acids may be adsorbed by soils and the adsorption could affect their biodegradation and efficiency in many soil processes. In the present study, the adsorption of phthalic acid and salicylic acid and their effect on the exchangeable Al capacity of variable-charge soils were investigated. The results indicated that phthalic acid and salicylic acid were adsorbed by four variable-charge soils to some extent, oxisols showed a greater adsorption capacity for organic acids than ultisols, and the ability of the four variable-charge soils to adsorb the organic acids at different pH generally followed the order Kunming oxisol > Xuwen oxisol > Jinxian ultisol > Lechang ultisol, which was closely related to their content of free iron oxides and amorphous iron and aluminum oxides. The adsorption of organic acids induced a decrease in the zeta potentials of soils and oxides. Goethite has greater adsorption capacity for organic acid than Xuwen oxisol and the adsorption of organic acids resulted in a bigger decrease in the zeta potential of goethite suspensions. After free iron oxides were removed, less organic acid was adsorbed by Xuwen oxisol and no change was observed in zeta potential for the soil suspension after organic acid was added. The presence of phthalic acid increased the capacity of exchangeable Al and the increment in the four variable-charge soils also followed the order Kunming oxisol > Xuwen oxisol > Lechang ultisol and Jinxian ultisol. The presence of salicylic acid increased the capacity of exchangeable Al in Kunming oxisol, Xuwen oxisol, and Jinxian ultisol, but decreased it in Lechang ultisol due to less adsorption of the acid and formation of soluble Al–salicylate complexes in solution. After free iron oxides were removed, less effect of organic acid on exchangeable Al was observed for Xuwen oxisol, which further confirmed that the iron oxides played a significant role in organic acid adsorption and had a consequent effect on the capacity of exchangeable Al in variable-charge soils. Therefore, the higher the content of iron oxides, the greater the adsorption of organic acids by soils and the greater the increase in soil exchangeable Al induced by the organic acids.
Keywords: Adsorption; Organic acids; Zeta potential; Exchangeable Al; Variable-charge soil;
Sodium, ammonium, calcium, and magnesium forms of zeolite Y for the adsorption of glucose and fructose from aqueous solutions by Misket Heper; Lemi Türker; N. Suzan Kincal (11-15).
The kinetics of adsorption by sodium, ammonium, calcium and magnesium forms of zeolite Y from aqueous solutions containing 25% w/v of either one or an equimolar mixture of glucose (G) and fructose (F) have been studied batch-wise at 50 °C. The adsorption of aqueous pure G was fast, while that of aqueous pure F depended on the cationic form, approaching that of G on the Mg-Y, and slowing down in the sequence of Mg 2 + > NH 4 + > Ca 2 + > Na + of the cations. The adsorption behavior from solutions containing both G and F indicated significant hindering effects of F on G on Na-Y. Na-Y and Mg-Y did not exhibit rate-based selectivity, while Ca-Y an NH4-Y adsorbed G faster than F. Addition of CaCl2 to the mixture of Ca-Y and aqueous solution of G and F improved the separation, by hindering the adsorption of F. Addition of NH4Cl to the mixture of the sugar solution and NH4-Y, on the other hand, had a negative effect on the separation. NH4-Y was found to be desorbing about 30% of the adsorbed sugars and this value was found to be around 50% for Ca-Y. Re-adsorption experiments resulted in similar or somewhat higher percentages of amounts adsorbed compared to adsorption on fresh samples. Both NH4-Y and Ca-Y were found to be re-adsorbing around 50% of the sugars they adsorbed on fresh samples.Batch-wise adsorption studies at 50 °C showed Ca-Y to be the most selective among the cationic forms and selectivity improved further by the addition of Ca2+ ions to the solution.
Keywords: Zeolite Y; Adsorption; Glucose; Fructose; Glucose–fructose separation;
Effect of replacing a hydroxyl group with a methyl group on arsenic (V) species adsorption on goethite (α-FeOOH) by J.S. Zhang; R.S. Stanforth; S.O. Pehkonen (16-21).
Arsenate and methylated arsenicals, such as dimethylarsinate (DMA) and monomethylarsonate (MMA), are being found with increasing frequency in natural water systems. The mobility and bioavailability of these arsenic species in the environment are strongly influenced by their interactions with mineral surface, especially iron and aluminum oxides. Goethite (α-FeOOH), one of the most abundant ferric (hydr)oxides in natural systems, has a high retention capacity for arsenic species. Unfortunately, the sorption mechanism for the species is not completely understood, which limits our ability to model their behavior in natural systems. The purpose of this study is to investigate the effect of replacing a hydroxyl group with a methyl group on the adsorption behaviors of arsenic (V) species using adsorption edges, the influence of the background electrolyte on arsenic adsorption, and their effect on the zeta potential of goethite. The affinity of the three species to the goethite surface decreases in the order of AsO4 = MMA > DMA. The uptake of DMA and MMA is independent of the concentration of background electrolyte, indicating that both species form inner-sphere complexes on the goethite surface and the most charge of adsorbed DMA and MMA locates at the surface plane. Arsenate uptake increases with increasing concentrations of background electrolyte at pH above 4, possibly due to that the charge of adsorbed arsenate is distributed between the surface plane and another electrostatic plane. DMA and lower concentrations of MMA have small effect on the zeta potential, whereas the zeta potential of goethite decreases in the presence of arsenate. The small effect on zeta potential of DMA or MMA adsorption suggests that the sorption sites for the anions is not important in controlling the surface charge. This observation is inconsistent with most adsorption models that postulate a singly coordinated hydroxyls contributing to both the adsorption and the surface charge, but supports the thesis that the charge on the goethite surface comes primarily from protonation of the triply bound oxygen atoms on the surface.The adsorption of various arsenic species is a strong function of the structure of the surface complex as can be seen from the above four examples for the case of AsO4 onto the goethite surface. Therefore, detailed competitive adsorption experiments as well as experiments probing the effect of pH and ionic strength must be conducted. Proposed AsO4 surface complexes on the goethite surface.
Keywords: Arsenic (V); Adsorption; Goethite; Zeta potential; MMA;
Mechanistic examination of pre-exfoliating confinement of surface-active polystyrene nanobeads within pristine clay by Svetlana Khvan; Junkyung Kim; Sang-Soo Lee (22-27).
Hydrophobic polymer (PS) nanoparticles preformed through an emulsifier-free emulsion polymerization method were successfully incorporated into a gallery of pristine sodium montmorillonite via interfacial cation exchange. The polymer beads confined between clay nanosheets were capable of (1) preventing the silicate layers from restacking and (2) maintaining the exfoliated state of clay. The increase in the abundance of surface groups promoted adsorption of the nanobeads onto the silicate surface and eventually led to the establishment of strong polymer–clay interactions. These findings suggest that, on the basis of the obtained pre-exfoliated clay masterbatch, the presence of strong polymer–clay interactions could improve the mechanical performance of nanocomposites.Pre-exfoliating confinement of the positively charged polystyrene nanobeads in between individual sheets of pristine sodium montmorillonite clay via interfacial cationic exchange.
Keywords: Surface charge; Polystyrene nanobeads; Cationic exchange; Polymer–clay interactions;
Functionalization of single-walled carbon nanotube by the covalent modification with polymer chains by Hiromi Kitano; Kazutaka Tachimoto; Yasutaka Anraku (28-33).
A single-walled carbon nanotube (SWNT), which had been oxidized by incubation with a mixture of nitric acid and sulfuric acid to afford carboxyl groups at its ends, was incubated with an azo-type radical initiator carrying poly(2-methacryloyloxyethyl d-glucopyranoside) blocks at both ends (PMEGlc-initiator). Due to its high radical trapping activity, the SWNT could be coated with glycopolymers corresponding to the cloven macro-initiator (PMEGlc-SWNT). The PMEGlc-SWNT indicated a lectin (concanavalin A, Con A)-induced aggregation, and a buckey sheet composed of PMEGlc-SWNT could be used for the recovery of Con A from its aqueous solution. Furthermore, the carboxylated SWNT was also incubated with a terminal-aminated poly(N-isopropyl acrylamide) (PIPA) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide HCl salt (PIPA-SWNT). The PIPA-SWNT indicated a definite temperature-responsiveness in the turbidity of its dispersion. These methods would be promising to modify SWNT with various functional polymers.Glycopolymer radicals corresponding to the cloven macro-initiator were covalently fixed to the single-walled carbon nanotubes (SWNTs). The thermo-responsive polymers were also fixed to the SWNT by the condensation reaction.
Keywords: Covalent modification; Glycopolymer; Poly(N-isopropyl acrylamide); Single-walled carbon nanotube;
Wetting and electrical properties of the human hair surface: Delipidation observed at the nanoscale by Vincent Dupres; Dominique Langevin; Patrick Guenoun; Antonio Checco; Gustavo Luengo; Frédéric Leroy (34-40).
The electrostatic properties and the wetting behaviour of the human hair surface at the nanometric scale have been investigated by using atomic force microscopy (AFM). Surface potential imaging was used to determine the electrostatic properties while non-contact mode AFM was used to investigate the wetting properties of a test liquid, squalane. We have studied natural hair and hair in which different covalently (18-methyleicosanoic acid) and non-covalently bound fatty acids present at the cuticle surface were selectively extracted. This study shows how the removal of these acids causes various profound changes in hair wettability at the cuticle scale.
Keywords: Atomic force microscopy; Wetting; Surface tension; Hair surface; Surface potential;
Inorganic metallodielectric materials fabricated using two single-step methods based on the Tollen's process by Molly S.M. Peterson; Jason Bouwman; Aiqing Chen; Miriam Deutsch (41-49).
Two methods for preparing polycrystalline silver shells on colloidal silica spheres are reported. These do not include the use of organic ligands or metal seeding steps and are based on the Tollen's process for silvering glass. Reaction parameters such as temperature and reactant concentrations are adjusted to slow the reaction kinetics, which we find leads to preferential silver growth on the spheres. The resulting shells are polycrystalline and granular, showing highly uniform sphere coverage. Surface morphologies range from sparsely interconnected grains for shells ∼20 nm thick, to complete (yet porous) shells of interconnected silver clusters which are up to ∼140 nm in thickness. The extinction spectra of the core–shell materials are markedly different from those of smooth continuous shells, showing clear evidence that the granular shell geometry influences the plasmon resonance of the composite system. Spheres coated with shells 20–40 nm thick are also suitable for colloidal crystallization. Monolayers of self-assembled spheres with long-range ordering are demonstrated.Silver coated silica spheres are produced using a modified Tollen's process, without utilizing nanoparticle seeding or chemical functionalization. These spheres exhibit geometrically tunable extinction spectra despite the highly granular shell morphologies.
Keywords: Silver; Nanoshell; Plasmon; Fractal; Colloidal crystal;
Stabilization of hydroxyl-group-terminated SERS-marker molecules on μAg particles by silanization by Lixin Xia; Nam Hoon Kim; Kwan Kim (50-55).
Micrometer-sized Ag (μAg) powders are very efficient substrates for both the infrared and Raman spectroscopic characterization of molecular adsorbates assembled on silver. In particular, the Raman spectrum of organic monolayers on μAg powders is a surface-enhanced Raman scattering (SERS) spectrum. To use μAg powders as a core material for constructing molecular sensing/recognition units operating via SERS, it is first necessary to stabilize the SERS-marker molecules that are directly in contact with the μAg powders. One promising strategy is the fabrication of silica shells onto SERS-marker molecules, and herein we demonstrate its feasibility by choosing 4-mercaptophenol (4-MPH) as a model SERS-marker molecule. Due to the presence of the hydroxyl group of 4-MPH, silica was readily deposited onto μAg particles by the base-catalyzed hydrolysis of tetraethyl orthosilicate, and its subsequent condensation, to form a cagelike structure. The formation of silica shells was confirmed with infrared, Raman, and X-ray photoelectron spectroscopy, coupled with field emission scanning electron microscopy. We were able to tune the thickness of silica shells simply by varying the silanization reaction time.μAg powders covered with 4-mercaptophenol as SERS-marker molecules are readily coated with silica shells so that the powders can be used as a core material of molecular sensing/recognition units operating via SERS after target molecules are attached onto the silica layer.
Keywords: Silver; μ-Powder; Silica; Core–shell; SERS; Surface-enhanced Raman scattering;
Electrochemical formation of crooked gold nanorods and gold networked structures by the additive organic solvent by Chien-Jung Huang; Pin-Hsiang Chiu; Yeong-Her Wang; Cheng-Fu Yang; Shih-Wei Feng (56-65).
Crooked gold nanorods (CGNRs) and gold network structures are fabricated using a simple electrochemical approach. The growth solution is prepared by surfactant solution as micelle templates with isopropanol (IPA) solvent. The shape of crooked nanorods and networks structure depend on the amount of added IPA solvent. To investigate the influence of isopropanol solvent on the CGNRs, the amount of IPA was varied in the range from 0.05 to 0.2 mL. It was found that the aspect ratios (γ) of CGNRs were in the range from 1.06 to 1.46, and the UV–vis absorption measurement revealed a pronounced red-shift of the surface plasmon resonance (SPR) band from 532 to 560 nm. High-resolution transmission electron microscopy (HRTEM) showed that the formation of crooked nanorod structure was induced by aggregation of many small gold nuclei between the several large gold nanoparticles during growth, causing the small gold nuclei to link the gold nanoparticles. The CGNRs have a polycrystalline structure via the analysis from selected-area electron diffraction (SAED).
Keywords: Gold; Nanoparticles; Nanorods; Surfactant; Micelle; Electrochemical;
Light scattering study on the size and structure of calcium phosphate/hydroxyapatite flocs formed in sugar solutions by Judy Greenwood; Tom Rainey; William O.S. Doherty (66-71).
The formation, flocculation and sedimentation of calcium phosphate particles are among the main physico-chemical reactions that occur during the clarification of cane sugar juice. The mechanisms through which processes occur in juice clarification are still poorly understood. This study (being part of a comprehensive investigation to unravel these mechanisms) reports on the size and structure of calcium phosphate particles and aggregates in water and sugar solutions at 20 °C using the small angle laser light scattering technique. The average size of the primary calcium phosphate particles was in the range 10.4 ± 1.1 μm to 17.5 ± 1.2 μm and the scattering exponents, which describe the structure of the calcium phosphate flocs, varied from 1.97 to 2.76. The flocs formed without flocculant are more compact in water than those formed in sugar solution. The compactness of the flocs was also affected by pH of the solution. This effect has been explained by considering the electrical double layer phenomenon.Calcium phosphate flocs formed in sucrose solution in the presence of a co-polymer of acrylamide and acrylic acid.
Keywords: Fractal dimension; Flocs; Calcium phosphate; Flocculation;
Extended cell average technique for the solution of coagulation equation by Margaritis Kostoglou (72-81).
Sectional (zero order) methods constitute a very important class of methods for the solution of the population balance equation offering distinct advantages compared to their competitors, namely, higher order and moment methods. For the last ten years a particular sectional method, the so-called fixed pivot technique has been the most extensively used in the scientific community for the solution of the coagulation equation because it offers arbitrary grid choice and conservation of two moments of the particle size distribution. Very recently, a new method (called cell average technique) has been developed which gives more accurate results than the fixed point technique. In the present work, the extension of this new method in order to conserve three moments is attempted. A stable algorithm for the solution of the coagulation equation is developed. Although the new method allows improved computation of moments of practical interest, this is not always the case with respect to complete particle size distribution.A novel sectional method for the solution of the coagulation population balance equation is developed based on the recent cell average technique with the added new feature of conservation of three moments of the particle size distribution.
Keywords: Coagulation equation; Population balance; Sectional methods; Numerical solution;
Characterization limits of a polymer adsorbed under a monolayer by GIXD measurements by Fabrice Goubard; Odile Fichet; Dominique Teyssié; Philippe Fontaine; Michel Goldmann (82-88).
The study of interactions between a polyelectrolyte (sodium polystyrene sulfonate, PSSt) or its water-soluble monomer (SSt) at different concentrations and a monolayer of dioctadecyldimethylammonium bromide (DODA) has been investigated. The monolayer phase behavior and structure at the air–water interface were studied by surface pressure–area isotherms and grazing incidence X-ray diffraction measurements. DODA molecules organize following a rectangular unit cell in all three subphases (pure water, water containing SSt or PSSt). The presence of polyelectrolytes in the subphase decreases, on one hand, the tilt angle and the mean area per molecule in the condensed phase, revealing a higher 2D density in this state, and, on the other hand, the amount of organized matter.Do GIXD measurements allow the determination of the structure of a polymer adsorbed under a Langmuir monolayer? Information can indirectly be obtained indirectly from the combination of measurements carried out on monolayers stabilized on various subphases.
Keywords: Dioctadecyldimethylammonium bromide; Langmuir monolayer; Grazing incidence X-ray diffraction measurements; Styrene sulfonate; Polymerization;
One-step incorporation of Pd–Zn catalytic sites into organized mesoporous alumina for use in the oxidative steam reforming of methanol by E. Moretti; M. Lenarda; L. Storaro; R. Frattini; P. Patrono; F. Pinzari (89-95).
In this paper we report the preparation of an organized mesoporous Pd–Zn/alumina system, by a new surfactant-assisted single-step sol–gel synthesis, performed in alcohol, using stearic acid as a chemical template, aluminum sec-butoxide as Al source and metal stearates both as Pd–Zn sources and as structural directing agents. The prepared materials have been characterized using a variety of techniques such as thermogravimetric analysis, atomic absorption spectroscopy, X-ray powder diffraction and N2 adsorption–desorption, and preliminarily tested in the oxidative steam reforming of methanol (OSRM) in the temperature range 100–400 °C.A organized mesoporous Pd–Zn/Al2O3 system is prepared by a single-step sol–gel synthesis using stearic acid as template and metal stearates as Pd–Zn sources and structural directing agents.
Keywords: One-step synthesis; Organized mesoporous oxides; Mesoporous alumina; Pd/Zn alloy; H2 production; Oxidative steam reforming of methanol; PEM fuel cells;
Corrosion of copper in aerated acidic pickling solutions and its inhibition by 3-amino-1,2,4-triazole-5-thiol by El-Sayed M. Sherif; R.M. Erasmus; J.D. Comins (96-104).
Corrosion of copper in aerated acidic chloride pickling (0.5 M HCl) solutions and its inhibition by 3-amino-1,2,4-triazole-5-thiol (ATT) have been investigated using electrochemical techniques and weight-loss measurements, along with Raman spectroscopy. Electrochemical measurements for copper after varied immersion periods of 0, 24, and 48 h showed that the presence of ATT and the increase of its concentration significantly decrease cathodic, anodic, corrosion ( j Corr ) currents and corrosion rates ( K Corr ), as well as the dissolution currents at 300 mV vs Ag/AgCl, while increasing polarization resistance ( R p ), degree of surface coverage (θ) and inhibition efficiency (IE%) to a great extent. Weight-loss measurements after different immersion periods of 6 to 48 h revealed that the dissolution of copper decreased to a minimum and the corresponding IE% increased with increasing ATT concentration. The detection of ATT molecules on the copper surface by Raman spectroscopy indicated that inhibition of copper corrosion is achieved by strong adsorption of ATT molecules onto the copper surface.Potentiodynamic polarization curves for copper in aerated 0.5 M HCl after 0 (a), 24 (b), and 48 h (c) of electrode immersion without (1) and with 0.5 (2), 1.0 (3), and 5.0 mM 3-amino-1,2,4-triazole-5-thiol (ATT) (4) present.
Keywords: Aerated acidic pickling solutions; 3-Amino-1,2,4-triazole-5-thiol; Copper corrosion; Corrosion inhibition; Raman spectroscopy;
Co-current and counter-current imbibition in independent tubes of non-axisymmetric geometry by E. Unsal; G. Mason; N.R. Morrow; D.W. Ruth (105-117).
Experiments that illustrate and quantify the basics of co- and counter-current spontaneous imbibition have been conducted in a series of simple model pore systems. The fundamental pore geometry is a rod in an angled round-bottomed slot with the rod touching a capping glass plate. The capillaries thus formed by the surfaces of the slot, rod and plate do not have circular cross-sections but more complicated geometric structures with angular corners. The tubes formed at each side of the rod connect at both ends. A viscous, refined oil was applied from one end. For co-current experiments, the opposite end was left open to the atmosphere and oil imbibed into both tubes. For counter-current experiments the opposite end was sealed and connected to a sensitive pressure transducer. Oil imbibed into the smaller capillary and expelled air as a series of bubbles from the end of the larger capillary. Bubble snap-off was observed to be rate-dependent and occurred at a lower curvature than that of the cylindrical meniscus that just fits inside the tube. Only the corners of the larger capillary filled with oil during counter-current imbibition. Meniscus curvatures were calculated using the Mayer and Stowe–Princen method and were compared with actual values by measuring the capillary rise in the tubes; agreement was close. A simple model for co-current and counter-current imbibition has also been developed and the predictions compared with the experimental results. The model results were in agreement with the experiments. The experiments demonstrate that the capillary back pressure generated by the interfaces and bubbles in counter-current imbibition can slow the process significantly.A numerical model for co- and counter-current imbibition has been developed. Experiments were also carried on some simple precise model systems and the results were compared with the theoretical predictions.
Keywords: Imbibition; Co-current; Counter-current; Shape factor; Hydraulic radius; Mayer and Stowe–Princen theory;
Covalent molecular assembly of multilayer dendrimer ultrathin films in supercritical medium by Sreenivasa Reddy Puniredd; M.P. Srinivasan (118-127).
Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.Schematic of layer-by-layer molecular assembly of poly(amido amine) dendrimer on an anhydride-derivatized silicon substrate with interlayer covalent bonds, formed using supercritical carbon dioxide as the processing medium.
Keywords: Supercritical carbon dioxide; Dendrimer; Covalent molecular assembly; Ultrathin films;
Droplet behavior on flat and textured surfaces: Co-occurrence of Deegan outward flow with Marangoni solute instability by Edward Bormashenko; Yelena Bormashenko; Roman Pogreb; Oleg Stanevsky; Gene Whyman (128-132).
It is demonstrated experimentally that the solution droplet behavior is governed by the co-occurrence of outward hydrodynamic and surface tension (solute Marangoni) induced flows. Potassium ferrocyanide allows the effective visualization of the processes taking place in the droplet. Wetting properties of the substrate govern the shape evolution of the evaporated droplet. Quantitative estimation of the wetting properties of textured polymer surface is presented.Crown-like potassium ferrocyanide deposit formed on the polymer honeycomb relief (optical microscopy image).
Keywords: Droplet; Textured surface; Potassium ferrocyanide; Deposit; Surface tension induced flow; Outward flow;
Synthesis and photonic band calculations of NCP face-centered cubic photonic crystals of TiO2 hollow spheres by Yong-zheng Zhu; Yan-ling Cao; Zhi-hui Li; Juan Ding; Jun-song Liu; Yuan-bin Chi (133-136).
With the help of self-assembly, thermal sintering, selective etching techniques and sol–gel process, the non-close packed (ncp) face-centered cubic (fcc) photonic crystals of titanium dioxide (TiO2) hollow spheres connected by TiO2 cylindrical tubes have been fabricated using silica template. The photonic bandgap calculations indicate that the ncp structure of TiO2 hollow spheres was easier to open the pseudogaps than close packed system at the lowest energy.Diagram showing the steps of fabrication the photonic crystals of TiO2 hollow spheres connected by cylindrical tubes. (a) SiO2 opal, (b) sintered (1010 °C), (c) after etching by HF acid solution, (d) coated with titania, (e) photonic crystals of TiO2 hollow spheres connected by cylindrical tubes.
Keywords: Hollow spheres; Non-close pack; Photonic crystal; Photonic bandgap;
Effect of organized assemblies by Sagarika Panigrahi; Moumita Chakravorty; Pramila K. Misra (137-142).
The dissociation constants (pK's) of aldimines, (o/p) hydroxybenzylidene-(4/6)-nitro-2-aminobenzothiazoles, have been determined spectrophotometrically in the absence and presence of ionic and nonionic surfactant assemblies at 27 °C. Substantial shifts in the pK's of the aldimines has been observed in the presence of the organized assemblies compared to water. The results have been attributed to the surface charge of the micelle, the effective hydrophobicity of the surfactants, and field and resonance effects due to NO2 group substitution. Surfactant assemblies are found to have randomly arranged hydrophobic chains leading to exposure of some of the hydrocarbon chain segments to bulk water. The results also support the presence of intramolecular H-bonding in the o-hydroxybenzylidene-(4/6)-nitro-2-aminobenzothiazoles.The pK's of a few aldimines, (o/p) hydroxybenzylidene-(4/6)-NO2–2-aminobenzothiazoles, have been studied spectrophotometrically. The pK's are found to be affected by both substitution in the aldimines and their environments. The data also support the Menger model of micelles.
Keywords: Aldimines; Dissociation constant; pK shift in organized assemblies; Menger micelle; Intramolecular H-bonding;
Unusually large acrylamide induced effect on the droplet size in AOT/Brij30 water-in-oil microemulsions by Allan K. Poulsen; Lise Arleth; Kristoffer Almdal; Anne Marie Scharff-Poulsen (143-153).
Droplet microemulsions are widely used as templates for controlled synthesis of nanometer sized polymer gel beads for use as, e.g., nanobiosensors. Here we examine water-in-oil microemulsions typically used for preparation of sensors. The cores of the microemulsion droplets are constituted by an aqueous component consisting of water, reagent monomer mixture, buffer salts, and the relevant dyes and/or enzymes. The cores are encapsulated by a mixture of the surfactants Brij30 and AOT and the resulting microemulsion droplets are suspended in a continuous hexane phase. The size of the final polymer particles may be of great importance for the applications of the sensors. Our initial working hypothesis was that the size of the droplet cores and therefore the size of the synthesized polymer gel beads could be controlled by the surfactant-to-water ratio of the template microemulsion. In the present work we have tested this hypothesis and investigated how the monomers and the ratio between the two surfactants affect the size of the microemulsion droplets and the microemulsion domain. We find that the monomers in water have a profound effect on the microemulsion domain as well as on the size of the microemulsion droplets. The relation between microemulsion composition and droplet size is in this case more complicated than assumed in standard descriptions of microemulsions [R. Strey, Colloid Polym. Sci. 272 (1994) 1005–1019; I. Danielsson, B. Lindman, Colloids Surf. 3 (1981) 391–392; Y. Chevalier, T. Zemb, Rep. Progr. Phys. 53 (1990) 279–371].
Keywords: Microemulsion; Acrylamide; Nanobiosensors; AOT; Brij30; Polymer particles; Nanoparticles; Modulation of micelle size;
Multi-phase equilibrium microemulsions and synthesis of hierarchically structured calcium carbonate through microemulsion-based routes by Liping Liu; Dawei Fan; Hongzhi Mao; Xi Fang; Jingcheng Hao (154-160).
Middle-phase microemulsions (MPMs) in two systems of a cationic surfactant, tetradecyltrimethylammonium bromide (TTABr)/n-butanol/iso-octane/Na2CO3 or CaCl2 and an anionic surfactant, sodium dodecyl sulfate (SDS)/n-butanol/iso-octane/Na2CO3 or CaCl2, were used to synthesize nanostructured calcium carbonates. MPMs provide a simple and versatile reaction media, i.e., upper-phase W/O, BC, and O/W structured equilibrium microemulsions to be used for synthesizing hierarchically structured CaCO3 at the nanometer scale. On the basis of the investigations on the phase behavior of the MPMs, hierarchically structured calcium carbonates with dendrites, ellipsoids, square-schistose cubes, and spheres were synthesized through the MPM-based routes.Middle-phase microemulsions provide a simple and versatile reaction media, i.e., upper-phase W/O, BC, and O/W structured equilibrium microemulsions to be used for synthesizing hierarchically structured CaCO3 at the nanometer scale, which should open alternative pathways to synthesize complex superstructures of inorganic materials, and construct the correlation between the morphologies of CaCO3 and the structures of microreactor media.
Keywords: Calcium carbonate; Microemulsions; Surfactants; Scanning electron microscope;
Influence of electrolytes/non-electrolytes on the cloud point phenomenon of the aqueous promethazine hydrochloride drug solution by Md. Sayem Alam; Andleeb Z. Naqvi; Kabir-ud-Din (161-165).
We have studied the clouding phenomena in promethazine hydrochloride (PMT) aqueous solutions in presence of electrolytes and non-electrolytes. PMT, a tranquillizer, shows phase separation. The cloud point (CP) decreases with increase in pH due to deprotonation of drug molecules. At constant pH, increasing salt addition causes an increase in CP, which is explained on the basis of their position in Hofmeister series and their hydrated radii. With quaternary salts CP increases due to adsorption/mixed micelle formation. Ureas decrease the CP and the behavior is explained on the basis of removal of water from the headgroup region.Effect of pH on the CP of 50 mM PMT solution, prepared in 10 mM sodium phosphate buffer, containing no or a fixed salt concentration (50 mM).
Keywords: Phenothiazine drug; Promethazine hydrochloride; Cloud point; Hofmeister series; Mixed micelles;
Effect of terbium(III) chloride on the micellization properties of sodium decyl- and dodecyl-sulfate solutions by A.C.S. Neves; A.J.M. Valente; H.D. Burrows; A.C.F. Ribeiro; V.M.M. Lobo (166-174).
The effect of TbCl3 on the aggregation processes of the anionic surfactants sodium decyl sulfate (SDeS) and sodium dodecyl sulfate (SDS) has been investigated. Electrical conductivity data, combined with Tb(III) luminescence measurements suggest that the formation of micelles involving TbCl3 and SDS occurs at concentrations below the critical micelle concentration (cmc) of the pure surfactants; the formation of these mixed aggregates was also monitored by light scattering, which indicates that the addition of TbCl3 to surfactant concentration at values below the pure surfactant cmc results in a much greater light scattering than that found with pure sodium alkylsulfate surfactant micelles. This phenomenon is dependent upon the alkyl chain length of the surfactant. With Tb(III)/DS−, complexes are formed with a cation/anion binding ratio varying from 3 to 6, which depends upon the initial concentration of Tb(III). This suggests that the majority of the cation hydration water molecules can be exchanged by the anionic surfactant. When the carbon chain length decreases, interactions between surfactant and Tb(III) also decrease, alterations in conductivity and fluorescence data are not so significant and, consequently, no binding ratio can be detected even if existing. The surfactant micellization is dependent on the presence of electrolyte in solution with apparent cmc being lower than the corresponding cmc value of pure SDS.
Keywords: Terbium(III); Sodium dodecyl sulfate; Sodium decyl sulfate; Micellization parameters; Aggregation;
Study of the surface energy of montmorillonite using PACHA formalism by J.M. Douillard; F. Salles; S. Devautour-Vinot; A. Manteghetti; M. Henry (175-182).
The surface energy of exchanged forms of montmorillonite has been computed using a partial charge model introduced in the calculation of the lattice energy. The results are in correct agreement with data on heats of adsorption. However, the difference between theoretical and experimental data increases from light cations to heavy cations associated with the clay network. This indicates that the heat of adsorption depends highly on the step hydration of the cations. This type of behavior was expected and thus the quantification seems realistic.In this paper, we focus on montmorillonite substituted with first column cations in our studies of the surface energy of clays. Heats of immersion and calculations of solid surface energy are linked in view of comparison of results. Data and calculations follow the expected trends and allow the prediction of hydration heats of the various cations.
Keywords: Solid surface energy; Montmorillonite; Electronegativity; Lattice energy;
Bromide and iodide removal from waters under dynamic conditions by Ag-doped aerogels by M. Sánchez-Polo; J. Rivera-Utrilla; U. von Gunten (183-186).
The objective of this study was to analyze the efficiency of Ag-doped aerogels in the removal of bromide and iodide from water. To test the applicability of these aerogels in water treatment, adsorption of bromide and iodide was studied under dynamic conditions using waters from Lake Zurich and a mineral water. The results obtained by using these waters showed a high breakthrough volume ( V 0.02 = 0.4 L ) of the columns, while the height of the mass transfer zone ( H MTZ = 6.8 cm ) was low, regardless of the anion under study. Bromide- and iodide-saturated columns were regenerated with NH4OH. No change in the column characteristics was observed after two regeneration treatments, regardless of the type of water considered.The results obtained after the aerogel regeneration process indicate its high efficiency, with a recovery of about 100% of the adsorptive capacity of the aerogel.
Keywords: Ag-doped aerogel; Halides; Adsorption; Dynamic conditions;
Sessile droplet de-pinning: New life for gravimetric data by Kwaichow B. Chan; Scott M. Pierce (187-191).
Using three different types of surfaces as exemplars, we report a gravimetric method as a viable tool for studying the de-pinning process. Namely, the de-pin time, τ d (the time required for a horizontal sessile droplet to de-pin at the triple phase line on a given substrate), is estimated without using a time consuming and expensive video imaging system. This is made possible by deciphering the non-linear portion of mass vs time data of an evaporating sessile droplet. Typical gravimetric glass-substrate evaporative mass loss vs time data has two regimes: a long, linear regime followed by a short, non-linear regime. Traditionally, researchers extract only the evaporation rate of a droplet from the linear regime but discard (by truncating the data) or ignore (thus deriving no information from) the non-linear regime. The origin of the linear to non-linear transition, found almost universally in gravimetric data, persists unremarked upon. By constructing three very different types of surfaces and comparing gravimetric data with video imaging data taken simultaneously, we report the transition is correlated to the onset of the de-pinning event in each case. This realization enables us to measure the de-pin time, τ d , with gravimetric data only; i.e., without the video system, gathering more information from gravimetric data than previously considered. The method has application in estimating the de-pin time of a droplet deposited on a substrate that yields poor top-view contrast for videography, such as a water droplets on silicon wafers or glass substrates. Finally, gravimetric data is more accurate for evaporation modeling when substrate/droplet interaction areas are not circular.By plotting mass-loss due to evaporation and area exposed to a substrate against time, we discover the beginning of the sessile droplet de-pinning event corresponds to the time at which the evaporative mass-loss curve deviates from linear. We use this to predict de-pinning events using only an analytical balance and a microprocessor.
Keywords: Sessile droplet evaporation; Contact angle; De-pinning; Gravimetric analysis;
Corrigendum to “Study of the surface character as responsible for controlling interfacial forces at membrane–feed interface” [J. Colloid Interface Sci. 303 (2006) 388–403] by A. Gugliuzza; R. Fabiano; M.G. Garavaglia; A. Spisso; E. Drioli (192-193).