Journal of Colloid And Interface Science (v.320, #1)
Quantitative determination of α-tocopherol distribution in a tributyrin/Brij 30/water model food emulsion
by Verónica Sánchez-Paz; Maria José Pastoriza-Gallego; Sonia Losada-Barreiro; Carlos Bravo-Díaz; K. Gunaseelan; Laurence S. Romsted (pp. 1-8).
Until recently, determining the distribution of antioxidants, AOs, between the oil, interfacial and aqueous regions of opaque emulsions has not worked well because the concentrations of AOs in interfacial regions cannot be determined separately from their concentrations in the oil and water phases. However, our novel kinetic method based on the reaction between an arenediazonium ion and vitamin E, or α-tocopherol, provides the first good estimates for the two partition constants that describe α-tocopherol distribution between the oil/interfacial and water/interfacial regions of tributyrin/Brij 30/water emulsions without physical isolation of any phase. The reaction is monitored by a new derivatization method based on trapping unreacted arenediazonium ion as an azo dye and confirmed by linear sweep voltammetry, LSV. The results by both derivatization and LSV methods are in good agreement and show that α-tocopherol distributes strongly in favor of the interfacial region when the oil is tributyrin, e.g., ca. 90% when the surfactant volume fraction isΦI=0.01. The second-order rate constant for reaction in the interfacial region is also obtained from the results. Our kinetic method provides a robust approach for determining antioxidant distributions in emulsions and should help develop a quantitative interpretation of antioxidant efficiency in emulsions.We have employed a kinetic method to determine the partition constants that describe α-tocopherol distribution between the oil/interfacial and water/interfacial regions of an emulsion without physical isolation of any phase.
Keywords: Arenediazonium ions; Vitamin E; Pseudophase model; Emulsions; Partition constants; Antioxidants
Application of anionic micelle for dramatic enhancement in the quenching-based metal ion fluorosensing
by Paramita Das; Arabinda Mallick; Deboleena Sarkar; Nitin Chattopadhyay (pp. 9-14).
We introduce a simple and efficient strategy to enhance the efficiency of a quenching-based fluorosensor for metal ions by several orders of magnitude by using commercially available anionic surfactants varying hydrophobic chain length. Anionic surfactants with a proper choice of hydrophobic chain length at their optimum concentrations are efficient to boost up the efficiency of copper ion sensor dramatically. This simple and convenient strategy is, in general, applicable to quenching-based fluorosensors, new or established, in aqueous solution. It is powerful enough to transform a virtually non-sensor fluorophore to a sensor with a commendable efficiency with the help of proper surfactant. Thus, in this communication, light has been thrown on the application of surfactants toward increasing fluorosensing efficiency of a quenching based sensor.Sensing efficiency of quenching-based fluorosensors has been enhanced dramatically by using anionic micelles. The simple strategy is powerful enough to enable a cationic fluorophore to an efficient sensor for cations.
Keywords: Surfactant; Anionic micelle; Quenching-based fluorosensor; Sodium alkyl sulfate; Fluorescence quenching
Adsorption, desorption, and conformational changes of lysozyme from thermosensitive nanomagnetic particles
by N. Shamim; H. Liang; K. Hidajat; M.S. Uddin (pp. 15-21).
Adsorption of globular protein, lysozyme, on thermosensitive poly( N-isopropylacrylamide) coated nanomagnetic particles was studied at different temperatures and pHs. It was observed that a maximum amount of lysozyme was adsorbed at a temperature above the lower critical solution temperature (LCST) (32 °C ) of the polymer and at the isoelectric point (pI=11) of lysozyme. Desorption was carried out using either NaH2PO4 (pH 4) or NaSCN (pH 6) as the desorbing agents. Conformational changes in lysozyme on desorption from nanomagnetic particles was studied by circular dichroism and intrinsic fluorescence spectroscopy. Lysozyme desorbed by NaH2PO4 showed very little conformational changes while lysozyme desorbed by NaSCN showed significant conformational changes, and 87% enzymatic activity was retained in the desorbed enzyme for desorption by NaH2PO4.Schematic diagram of adsorption desorption of target molecule on thermosensitive nanomagnetic particles.
Keywords: N-; isopropylacrylamide; Lower critical solution temperature (LCST); Isoelectric point; Lysozyme; Conformational changes
Porogen effect on characteristics of banana pith carbon and the sorption of dichlorophenols
by M. Sathishkumar; K. Vijayaraghavan; A.R. Binupriya; A.M. Stephan; J.G. Choi; S.E. Yun (pp. 22-29).
Banana pith was used as precursor material to prepare carbon with and without porogens. Characterization of the carbons showed higher BET surface area (1285 m2/g) for ZnCl2-treated carbon, comparatively. Adsorption experiments were conducted to study the removal of 2,4-dichlorophenol (DCP) from aqueous solutions using the carbons under varying experimental conditions. Decrease in pH increased the percentage removal. All the carbons studied showed greater percentage of DCP removal with decrease in the initial concentration of DCP. Kinetic studies showed that the adsorption of DCP on the carbons was a rapid process. Nonlinear forms of pseudo-first-order and pseudo-second-order models were used to fit the experimental data. Among these the pseudo-first-order model described the data with high correlation coefficients and low percentage error values. Four nonlinear isotherm models including the Langmuir, Freundlich, Toth, and Sips were used to analyze the experimental DCP isotherms under different pH (2–4) conditions. Adsorption capacities (Qmax) from the Langmuir model were found to be 129.4, 67.7, and 49.9 mg/g for ZnCl2-treated, KOH-treated, and porogen-free carbon, respectively, at pH 2. From desorption studies it seemed that chemisorption played a major role in the adsorption process. The results indicated that ZnCl2-treated carbon could effectively remove phenols from wastewater.Increasing the porosity of the carbon increases the total surface area of carbon facilitating higher adsorption of the adsorbates.
Keywords: Banana pith; Carbon; Porogen; Surface area; DCP; Adsorption; pH; Isotherms; Kinetics; Desorption
Trimesic acid coated alumina: An efficient multi-cyclic adsorbent for toxic Cu(II)
by Bedabrata Saha; Saswati Chakraborty; Gopal Das (pp. 30-39).
Biodegradable and eco-friendly organic acid, benzene-1,3,5-tri-carboxylic acid (trimesic acid), coated on commercial basic alumina, was used as adsorbent to remove toxic Cu(II) ion from aqueous solution. Adsorbent preparation was optimized and was characterized by SEM, EDX, FT-IR, and powder XRD pattern. Effect of various regulating parameters like reaction pH, adsorbent dose and initial Cu(II) concentration was studied in detail. Adsorption isotherms followed the Langmuir isotherm model and adsorption was thermodynamically favourable. Maximum adsorption capacity (Qm) for Cu(II) ion has been achieved as 10.80 mg/g. Detail kinetic study revealed that it followed second-order rate. Desorption of Cu(II) ion and re-usability of the adsorbent was also studied.Trimesic acid coated alumina is an efficient, multi-cyclic adsorbent for toxic metal. It follows Langmuir adsorption pattern of second-order kinetic rate.
Keywords: Trimesic acid; Basic alumina; Adsorption isotherm; Adsorption kinetics; Desorption; Cu(II) removal
Carbon surface chemical composition in para-nitrophenol adsorption determined under real oxic and anoxic conditions
by Artur P. Terzyk; Marek Wiśniewski; Piotr A. Gauden; Gerhard Rychlicki; Sylwester Furmaniak (pp. 40-51).
A series of commercial unmodified and modified activated carbons was studied. The surface chemical composition was characterized using X-ray photoelectron spectroscopy and Boehm titration methods. Data on p-nitrophenol (pnp) adsorption isotherms determined under real oxic and anoxic conditions (at 310 K) are presented and described using bimodal Langmuir and lattice density functional theory models. The applicability of the pnp molecule for determination of surface area using adsorption from solution data is discussed. It is shown that under anoxic conditions adsorption and relative enthalpy of this process depend on the value of BET apparent surface area and DA micropore volumes. The differences between adsorption levels under both conditions increase with rise in solute equilibrium concentration. Moreover, the average difference between adsorption values under both conditions increases and next decreases with rise in the concentration of surface acidic groups. Applying quantum chemical calculations, we show that under anoxic conditions the influence of surface oxygen groups on pnp adsorption is small, whereas under oxic conditions the reverse situation is observed. Obtained theoretical results show very good correspondence to the experimental data and the origin of the relationships observed experimentally is explained and discussed.Schematic representation of carbon model applied under anoxic and oxic conditions, together with experimental pnp isotherms (center).
Keywords: Adsorption from solution; p; -Nitrophenol adsorption; Activated carbon; Oxidative coupling
High-impact polystyrene/polyaniline membranes for acid solution treatment by electrodialysis: Preparation, evaluation, and chemical calculation
by F.D.R. Amado; M.A.S. Rodrigues; F.D.P. Morisso; A.M. Bernardes; J.Z. Ferreira; C.A. Ferreira (pp. 52-61).
In this study different membranes were produced, aiming to evaluate their use in electrodialysis. These membranes were produced using conventional polymer (high-impact polystyrene) and polyaniline. The membrane characterization was done by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetry (TGA). The studies of the zinc and proton extraction ionic transport through the membranes were evaluated using a three-compartment cell. The results obtained using the produced membranes were compared to the results obtained with the commercial membrane Nafion 450. It was found that a synthesized membrane can be used to recover zinc in acid media. In addition, a preliminary computational essay about the structures of PAni and CSA is presented.The performance of HIPS/PAni-CSA and Nafion commercial membrane was compared, when used treatment of zinc solutions. Complementary, we have performed structure calculations to study experimental phenomena involved during ionic transport.
Keywords: HIPS; Membrane; Electrodialysis; Polyaniline; Chemical calculation
Linear poly(ethylenimine)- graft-poly(ethylene glycol) copolymers: Their micellization and secondary assembly
by Huanbing Wang; Xuesi Chen; Caiyuan Pan (pp. 62-69).
Linear poly(ethylenimine)- graft-poly(ethylene glycol)s (LPEI- g-PEG) with various degrees of grafting and molecular weights were synthesized by Michael addition reaction of LPEI with methoxy poly(ethylene glycol) acrylate. The graft copolymers display pH-sensitive behaviors, and pH variation of the copolymer solution induced the aggregation of graft copolymers, forming the micelles with different sizes. The dynamic light scattering method was used to study the effects of ionic strength, chain composition and pH on hydrodynamic radius. With solvent evaporation of the micelles solution, various morphologies were formed.The graft copolymers LPEI- g-PEG have been synthesized by a combination of ring- opening and Michael addition polymerizations. They display pH-sensitive behavior, and aggregation of graft copolymers yielded micelles with different sizes. The ionic strength, pH, and chain compositions affect the hydrodynamic radius. Evaporation of polymeric solution yielded various morphologies.
Keywords: Self-assembly; Secondary assembly; pH-sensitive; Poly(ethylenimine)
Micellar and surface properties of a poly(methyl methacrylate)–block–poly( N-isopropylacrylamide) copolymer in aqueous solution
by Antonios Kelarakis; Tian Tang; Vasiliki Havredaki; Kyriakos Viras; Ian W. Hamley (pp. 70-73).
Critical micelle concentrations (cmc) of aqueous solutions of poly(methyl methacrylate)–block–poly( N-isopropylacrylamide) were determined at several temperatures by surface tensiometry. Below the lower critical solution temperature (LCST), the lowΔmicH0 determined can be assigned to the PMMA block being tightly coiled in the dispersed molecular state, so that the unfavorable interactions of hydrophobic entities with water are minimized. Above the LCST the cmc value was found to increase; an anomalous behavior that can be directly related to the micelle–globule transition of the hydrophilic block. Interestingly, above the LCST the surface tension of relatively concentrated solutions was found to depend weakly on temperature not following the usual strong decrease with temperature expected for aqueous solutions.At low temperatures, surface tensiometry in aqueous solutions of PMAA– b–PNIPAm copolymer reveals a case of almost athermal micellization.
Keywords: Critical micelle concentration; Surface properties; Thermoresponsive aggregation
Polymer–surfactant interactions: Binding mechanism of sodium dodecyl sulfate to poly(diallyldimethylammonium chloride)
by Gilat Nizri; Serge Lagerge; Alexander Kamyshny; Dan T. Major; Shlomo Magdassi (pp. 74-81).
The binding mechanism of poly(diallyldimethylammonium chloride), PDAC, and sodium dodecyl sulfate, SDS, has been comprehensively studied by combining binding isotherms data with microcalorimetry, zeta potential, and conductivity measurements, as well as ab initio quantum mechanical calculations. The obtained results demonstrate that surfactant–polymer interaction is governed by both electrostatic and hydrophobic interactions, and is cooperative in the presence of salt. This binding results in the formation of nanoparticles, which are positively or negatively charged depending on the molar ratio of surfactant to PDAC monomeric units. From microcalorimetry data it was concluded that the exothermic character of the interaction diminishes with the increase in the surfactant/polymer ratio as well as with an increase in electrolyte concentration.Left: zeta potential of SDS-PDAC complex as a function of r (the charge molar ratio between the SDS and PDAC), and right: the complex formation stages.
Keywords: Polyelectrolyte–surfactant interaction; Microcalorimetry; Binding isotherms; Cooperative binding; Molar conductivity
Entrapment of functionalized silica microspheres with photo-initiated acrylate-based polymers
by Graham T.T. Gibson; Terry B. Koerner; Ruixi Xie; Kalpa Shah; Nevin de Korompay; Richard D. Oleschuk (pp. 82-90).
The entrapment of silica-based microspheres, commonly used as stationary phases in chromatography, with an organic porous polymer based on poly(butyl acrylate- co-1,3-butanediol diacrylate) was explored. The spheres were immobilized by photopolymerization leading to entrapped beds within 75 μm i.d. fused silica capillaries, and were mechanically stable, resisting pressure drops of over 5600 psi (38.6 MPa) for only 1 cm of material. The morphology of the polymer formation around the spheres was investigated by SEM and corroborated with back pressure measurements, which indicated that the spheres were held together by encapsulating polymer. The entrapped material was extruded from the capillary in some cases to facilitate imaging. The entrapment conditions were explored, varying the polarity of the sphere surface, the solvent, and the monomers, revealing that polymer formation is based on partitioning of the monomers between the surface and solvent. The resulting polymer morphology is discussed with respect to the effects of confinement, supported by experiments with varying microsphere diameters. The columns described here have favourable properties for use in capillary chromatography and supported catalysis among other applications, and is suitable for lab-on-a-chip devices.Functionalized silica microspheres are entrapped such that polymer forms only on the surface of the spheres, where the resulting material is robust enough to be extruded from a capillary.
Keywords: Entrapped microspheres; Core–shell composite; Surface–solvent interface; Polymer thin film; Confinement; Column
Superhydrophobicity of PHBV fibrous surface with bead-on-string structure
by Young Il Yoon; Hyun Sik Moon; Won Seok Lyoo; Taek Seung Lee; Won Ho Park (pp. 91-95).
A poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) fibrous surface with various bead-on-string structures was fabricated by electrospinning. PHBV was electrospun at various concentrations and then CF4 plasma treatment was employed to further improve the hydrophobicity of the PHBV fiber surfaces. The surface morphology of the electrospun PHBV mats was observed by scanning electron microscopy (SEM). The surface properties were characterized by water contact angle (WCA) measurements and X-ray photoelectron spectroscopy (XPS). The surface morphology of the electrospun PHBV fibrous mats with the bead-son-string structure varied with the solution concentration. The WCA of all of the electrospun PHBV mats was higher than that of the PHBV film. In particular, a very rough fiber surface including porous beads was observed when PHBV was electrospun from the solution with a concentration of 26 wt%. Also, its WCA further increased from 141° to 158° after CF4 plasma treatment for 150 s. PHBV can be rendered superhydrophobic by controlling the surface morphology and surface energy, which can be achieved by adjusting the electrospinning and plasma treatment conditions.The water contact angles of all of the electrospun PHBV mats were much higher than that of the PHBV film.
Keywords: Superhydrophobicity; Poly(3-hydroxybutyrate-; co; -3-hydroxyvalerate) (PHBV); Beaded fibers; Electrospinning; Plasma treatment
Influence of crystallite microstrain on surface complexes governing the metastable equilibrium solubility behavior of carbonated apatites
by Kongnara Papangkorn; Guang Yan; Dustin D. Heslop; Kunikazu Moribe; Arif A. Baig; Makoto Otsuka; William I. Higuchi (pp. 96-109).
This study was on the influence of the mineral phase crystallite microstrain (CM) on the nature of the surface complex (SC) governing the metastable equilibrium solubility (MES) behavior of carbonated apatites (CAPs) in aqueous acidic media (0.10 M acetate buffers, with and without fluoride, 0.50 M ionic strength maintained with NaCl). The MES behavior of a set of four CAPs (synthesized at 85 °C by a precipitation method) of increasing CM and therefore of increasing MES (CAP4 > CAP3 > CAP2 > CAP1) was quantified. The following were the findings. For CAP1 and CAP2, the SCs deduced were Ca10(PO4)6(OH)2 and Ca10(PO4)6F2 for the nonfluoride and the fluoride cases, respectively. For CAP3 and CAP4, the SCs deduced were Ca9.5(PO4)6OH or Ca9.5(HPO4)(PO4)5(OH)2 and NaCa9.5(PO4)6F2 for the nonfluoride and the fluoride cases, respectively. These results together with that from an earlier limited study show that the Ca/P ratio of the SC decreases from 1.67 to 1.58 to 1.50 with increasing CM of the CAPs; this relationship inversely correlates with the chemistry of maturation of aqueously precipitated defective apatites. Also the SCs do not appear to exist as a continuous series and only a few SCs may account for the MES behavior over a wide range of CAP preparations.Surface complexes governing carbonated apatite solubility behavior: with increasing crystallite microstrain, solubility increases and the surface complex formula changes from that of stoichiometric hydroxyapatite to those with decreasing Ca/P ratios.*For comparison purposes, the CAP solubilities are at 50% dissolved and pH 5.7, and are expressed by the ion activityproduct=(aCa)10(aPO4)6(aOH)2.**This formula is indistinguishable from Ca9.5(HPO4)(PO4)5(OH)2.
Keywords: Carbonated apatite; Solubility; Metastable equilibrium solubility; Surface complex; Crystallite microstrain; Hydroxyapatite; Fluorapatite
Fibronectin adsorption on gold, Ti-, and Ta-oxide investigated by QCM-D and RSA modelling
by Anne Gry Hemmersam; Kristian Rechendorff; Morten Foss; Duncan S. Sutherland; Flemming Besenbacher (pp. 110-116).
The adsorption of fibronectin on gold, Ti-, and Ta-oxide surfaces is investigated by means of the quartz crystal microbalance with dissipation (QCM-D) technique. The surface chemistry (gold, Ti-, and Ta-oxide) is found to influence the frequency shift observed during adsorption of the fibronectin layer with the magnitude beingΔfAu>ΔfTi-oxide∼ΔfTa-oxide. Corresponding variations in the dissipation change normalised to frequency change (ΔD/Δf) for the layer are observed. The QCM-D data are further analyzed by the random sequential adsorption (RSA) model, and adsorption rate parameterka and footprint (a) determined, which supported the trend seen in the Δ f andΔD/Δf values. The value ofka found by the RSA modelling of the QCM-D resonance frequency data is found to match the ratio between the mass measured by QCM-D and the mass reported by optical techniques in literature. We conclude that comparison of the adsorption rate parameter (ka) obtained by RSA modelling of the QCM-D data withka values obtained from RSA modelling of data obtained using optical techniques can be a route to determine the degree of hydration of the adsorbed protein layer.Adsorption rate vs the surface mass density for fibronectin adsorption on gold. Quartz crystal microbalance with dissipation data and random sequential adsorption (RSA) fitting to the data are shown.
Keywords: Fibronectin; Random sequential adsorption (RSA); Quartz crystal microbalance (QCM-D); Gold; Titanium-oxide; Tantalum-oxide surfaces
Effect of UV irradiation on the surface Gibbs energy of Ti6Al4V and thermally oxidized Ti6Al4V
by M.A. Pacha-Olivenza; A.M. Gallardo-Moreno; A. Méndez-Vilas; J.M. Bruque; J.L. González-Carrasco; M.L. González-Martín (pp. 117-124).
Thermal oxidation of Ti6Al4V increases the thickness, modifies the structure, and changes the amount of alloying elements of the surface titanium dioxide layer with respect to the spontaneous passive layer of Ti6Al4V. The effects on the surface properties of Ti6Al4V and thermally oxidized Ti6Al4V after different periods of UV irradiation have been studied by measurement of water, formamide, and diiodomethane contact angles. The rate of modification of the water contact angle with the irradiation time is dependent on the surface treatment, but the water adhesion work, after an initial energetic step, follows a similar trend for both. Application of the Young equation together with the van Oss approach allowed evaluation of the surface Gibbs energy of the alloys. Similar to the water adhesion work, the surface Gibbs energy dependence on the irradiation time follows a similar trend for both samples and it is due to the change of the electron-donor parameter of the acid–base component. Also, a linear relationship common for both samples has been obtained between the cosines of the water contact angle and the formamide or diiodomethane contact angle. These facts indicate that the surface modification continuously produced by the UV irradiation is similar all along the process and similar for both samples after an energetic threshold for the thermally oxidized sample. It has been also tested that the hydrophilic–hydrophobic conversion is reversible for Ti6Al4V and Ti6Al4V thermally treated.Different intervals of UV irradiation on Ti6Al4V samples modify the cosine of formamide and diiodomethane linearly with the cosine of water contact angle.
Keywords: Surface Gibbs energy; Contact angle; Ti6Al4V; Biomaterials; UV radiation; Hydrophobicity
Fabrication, characterization, and application of potentiometric immunosensor based on biocompatible and controllable three-dimensional porous chitosan membranes
by Ruping Liang; Hongzhen Peng; Jianding Qiu (pp. 125-131).
A novel three-dimensional porous chitosan membrane material was prepared as a matrix to encapsulate hepatitis B surface antibody (HBsAb) for fabrication of immunosensors. The porous chitosan matrix was prepared by electrodepositing a designer nanocomposite solution of chitosan-encapsulated silica nanoparticle hybrid film on an ITO electrode, and then removing the silica nanoparticles with HF solution. Using HBsAb as a model, the potentiometric immunosensor was constructed by linking HBsAb molecules to the three-dimensional porous chitosan film using glutaraldehyde as a cross-linker. Scanning electron microscopy was used to investigate the surface morphology of the three-dimensional porous chitosan films. Cyclic voltammograms and electrochemical impedance spectroscopy were used to probe the interfacial properties of the immunosensor. Results showed that the fabricated immunosensor with three-dimensional porous structure possessed high surface area, good mechanical stability, and good hydrophilicity, which provided a biocompatible microenvironment for maintaining the bioactivity of the immobilized protein and increased the protein loading. Therefore, the present immunosensor exhibits a wide linear range from 6.85 to 708 ng mL−1 with a low detection limit of 3.89 ng mL−1 for the detection of hepatitis B surface antigen (HBsAg). This work implied that the biocompatible and controllable three-dimensional porous chitosan membrane possessed potential applications for biosensing.Three-dimensional porous chitosan membranes were fabricated by using an electrochemical deposition technique. The robust porous structure possessed high surface area, good mechanical stability, and good biocompatibility.
Keywords: Chitosan; Porous; Nanoparticle; HBsAg; Immunosensor
Silica nanoparticles encapsulating near-infrared emissive cyanine dyes
by Joseph F. Bringley; Thomas L. Penner; Ruizheng Wang; John F. Harder; William J. Harrison; Laura Buonemani (pp. 132-139).
We show that efficient near-infrared (NIR) cyanine fluorophores (1 and2) can be encapsulated into silica nanoparticles providing a highly versatile and unique platform for in vivo diagnostics. Utilizing this platform, multiple fluorophores can be loaded within a single particle allowing the light absorption and emission properties of the nanoparticle to be controlled independent of particle size. Furthermore, such dyed nanoparticles may have extinction coefficients as high as about100×106 Lmol−1cm−1 in the NIR (on a per mole of particles basis), with quantum yields from about 8–10%. A simple synthetic method for varying particle size and dye-loading level is presented, and a modified Stober synthesis reduces deleterious exposure of the dye to the highly alkaline conditions used. The cyanine dyes are encapsulated in silica in a non-aggregated state and the fluorescence brightness is largely maintained to nominal dye concentrations approaching 50 μM. The ability to control light absorption and emission properties independent of particle size, and convenient access to particle sizes in the range of 20–100 nm (a size regime difficult to access with other nanoparticle approaches such as quantum dots), are important features for anatomical targeting in in vivo diagnostics and targeted therapeutic applications.
Keywords: Near-infrared dyes; Nanoparticles; Fluorescent particles; Silica
Fluorescence resonance energy transfer between two cationic laser dyes in presence of the series of reduced-charge montmorillonites: Effect of the layer charge
by A. Czímerová; N. Iyi; J. Bujdák (pp. 140-151).
Series of montmorillonites with systematically reduced layer charges represent a suitable model for studying various properties and interactions of layered inorganic compounds. The reduced-charge montmorillonites (RCMs) used in this study were prepared by a standard method of Li+-fixation in Nanocor montmorillonite at 100–300 °C. The layer charge gradually decreased with increasing temperature of RCM preparation. Li+-fixation led in some cases to the loss of expandability due to the formation of mixed swelling/nonswelling and homogeneous nonswelling phases. The interaction of two cationic dyes—rhodamine 3B (R3B) and oxazine 4 (Ox4)—with reduced-charge montmorillonites in dispersions was studied by means of UV/vis absorption and fluorescence spectroscopy. Montmorillonite with the highest charge density induced the formation of H-aggregates of the dye cations characterized by a sandwich-type structure. As the layer charge decreased, the amount of the H-aggregates was reduced in favor of H-dimers and monomers. RCMs with low charge density suppressed dye cation aggregation and mainly monomeric forms were detected. The process of energy transfer from R3B to Ox4 was detected as decreasing the emission from the energy donor and increasing the emission from the energy acceptor. The energy transfer was clearly influenced by the properties of RCM templates. The dye cations adsorbed at the surface of the highest-charge specimen formed H-aggregates, which were efficient luminescence quenchers. Fluorescence resonance energy transfer (FRET) gradually increased with the charge reduction to be optimal at the templates with medium layer charge. Substantial decrease of the layer charge and reduction of clay mineral swelling led to the decrease of both the luminescence and the efficiency of FRET. The relations of energy transfer processes to the layer charges and swelling properties of montmorillonite are analyzed in detail.
Keywords: Fluorescence resonance energy transfer; Laser dyes; Layer charge; Reduced charge montmorillonites; Swelling
Synthesis of PVAc/SiO2 latices stabilized by silica nanoparticles
by Nangeng Wen; Qinqiong Tang; Min Chen; Limin Wu (pp. 152-158).
This paper presents a method for the preparation of raspberry-like organic–inorganic composite spheres with poly(vinyl acetate) (PVAc) as core and nanosilica particles as shell. A small amount of anionic reactive surfactant, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt (HAPS), was used as co-stabilizer and nanosilica particles were adsorbed onto the growing latex core in aqueous medium via the formation of hydrogen bonds between nanosilica particles and PVAc particles. TEM indicated that the hydrogen bonds between nanosilica particles and PVAc were strong enough for the formation of long-stable composite spheres with raspberry-like morphology. Influences of some synthetic parameters, for instance, type of silica sol, initial silica amount, and different kinds of low-molecular-weight surfactant, on the morphology of the composite spheres and properties of the latex films were studied in detail. A possible formation mechanism of the composite spheres was also proposed.PVAc/SiO2 organic–inorganic composite spheres were prepared via the formation of hydrogen bonds between silica nanoparticles and PVAc particles.
Keywords: Organic–inorganic composites; Silica nanoparticles; PVAc; Hydrogen bonds
Imaging c-PAM-induced flocculation of paper fibers
by William H. Hartley; Sujit Banerjee (pp. 159-162).
The flocculation of paper fibers by cationic polyacrylamides (c-PAM) was studied by imaging the fibers that remain free during flocculation. Studies with fibers of different lengths showed that the degree of flocculation increases with fiber length, with the best flocs being formed with mixtures of short and long fibers. Short fibers did not flocculate by themselves but were captured by flocs formed with longer fibers. The short fibers strengthen the floc and give it shear resistance. Shear had the expected effect of promoting flocculation at low Reynolds number but disrupting it at higher values. For a given polymer the maximum floc size for a mixture of fibers is dictated by the length distribution of the fibers. The polymer dose governs the rate of flocculation. The technique is especially useful in following the tail end of the flocculation process. At this stage a floc is almost fully grown and a small increase in its size would be very difficult to measure by conventional techniques. In contrast, the number of free fibers measured by single fiber imaging decreases rapidly at this point.
Keywords: c-PAM; Fiber; Floc; Polymer; Image
Metal nanoparticle formation in oil media using di(2-ethylhexyl) phosphoric acid (HDEHP)
by S. Bucak; A. Pugh-Jones; C. Lewis; D.C. Steytler (pp. 163-167).
The metal ion extractant (HDEHP) that is commonly employed in liquid membrane extraction has been shown to stabilise Ag and Cu nanoparticles in oil media of size 5 and 10 nm, respectively. The particle are formed by reduction of the metal salts of HDEHP that are oil soluble and shown by SANS to form small reversed micelles of radius ∼1 nm. The extractant is also effective at stabilising particles of similar size in an oil phase when the metal ion (e.g., AgNO3) is reduced in a coexisting aqueous phase.Hydrazine reduction of metal salts of the extractant di(2-ethylhexyl) phosphate in oil results in stable metal nanoparticles of significantly smaller size than obtained previously using this ligand.
Keywords: Nanoparticles; Copper; Silver; HDEHP
Chemical modification of zinc hydroxide nitrate and Zn–Al-layered double hydroxide with dicarboxylic acids
by Gregorio Guadalupe Carbajal Arizaga; Antonio Salvio Mangrich; José Eduardo Ferreira da Costa Gardolinski; Fernando Wypych (pp. 168-176).
A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2⋅2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate (−OOC(CH2)4COO−), azelate (−OOC(CH2)7COO−), and benzoate (C6H5COO−) ions through ion exchange reactions. Solid state13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratiog‖/A‖=170cm and, after intercalation of adipate, the change was not significant:g‖/A‖=174cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio tog‖/A‖=194cm, similar to the spectra of ZHN modified with adipate,g‖/A‖=199cm, and azelate,g‖/A‖=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.Possible arrangements of (a) adipate and (b) azelate ions between the layers of layered double hydroxides and (c) adipate, (d) azelate, and (e) benzoate ions in zinc hydroxide nitrate.
Keywords: Layered double hydroxide; Zinc hydroxide nitrate; Intercalation; Grafting; Surface chemical modification
An ATR-FTIR spectroscopic approach for measuring rapid kinetics at the mineral/water interface
by S.J. Parikh; B.J. Lafferty; D.L. Sparks (pp. 177-185).
This study presents a methodology for studying rapid kinetic reactions for IR active compounds. In soils, sediments, and groundwater systems a rapid initial chemical reaction can comprise a substantial portion of the total reaction process at the mineral/water interface. Rapid-scan attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy is presented here as a new method for collecting rapid in situ kinetic data. As an example of its application, the initial oxidation of arsenite (AsIII) via Mn-oxides is examined. Using a rapid-scan technique, IR spectra were collected with a time resolution of up to 2.55 s (24 scans, 8 cm−1 resolution). Through observation and analysis of IR bands corresponding to arsenate (AsV), rapid chemically-controlled AsIII oxidation is observed (initial pH 6–9) with 50% of the reaction occurring within the first one min. The oxidation of AsIII is followed by rapid binding of AsV to HMO, at least in part, through surface bound MnII. The experimental data indicate that rapid-scan FTIR is an effective technique for acquisition of kinetic data, providing molecular scale information for rapid reactions at the solid/liquid interface.Rapid-scan ATR-FTIR spectroscopy is presented to collect rapid kinetic data at the molecular scale.
Keywords: ATR-FTIR; Rapid kinetics; Mn-oxide; Arsenic
Novel application of depleted fullerene soot (DFS) as support of catalysts for low-temperature reduction of NO with CO
by I. Spassova; M. Khristova; R. Nickolov; D. Mehandjiev (pp. 186-193).
Depleted fullerene soot (DFS) with fullerene residue content of about 2.2–3.2% are investigated in order to elucidate the possibility for their use as support of catalysts in low-temperature reduction of NO with CO. Bimetalic copper–cobalt and copper–manganese oxides supported on DFS are prepared. All samples are characterized by chemical analysis, XRD, SEM, IR spectroscopy, XPS, nitrogen adsorption measurements. The two DFS supported bimetallic catalysts manifest a high activity towards the reduction of NO with CO at temperatures below 150 °C, the CuCo/DFS being the more active one. The peculiarity of the support DFS predetermines the porous texture of the catalysts. The occurrence of a specific metal–support interaction favors the formation of the mixed oxide spinels CuCo2O4 and Cu1.5Mn1.5O4 that are responsible for the enhanced activity.
Keywords: Depleted fullerene soot (DFS); Catalyst; Copper–cobalt oxide; Copper–manganese oxide; NO reduction; Porous texture
Cerium dioxide/polyaniline core–shell nanocomposites
by Feng-Yi Chuang; Sze-Ming Yang (pp. 194-201).
The preparation of CeO2/polyaniline (CeO2/PANI) core–shell nanocomposites via chemical oxidation of aniline using CeO2 as an oxidant is reported. TEM, TGA, FT-IR, XPS, and conductivity measurement are used to characterize the resulting composites. TEM measurements reveal that the shape of PANI/CeO2 nanocomposites is different from CeO2 nanoparticles and fibular PANI oxidized with soluble oxidant. Electron diffraction (ED) patterns of CeO2/PANI nanocomposites reveal single crystal of CeO2. FT-IR spectra confirmed the formation of PANI; the amount of PANI in the nanocomposites is estimated by TGA results. The conductivities increase with the increasing ratio of PANI/CeO2. XPS results reveal that in the nanocomposites Ce4+ of CeO2 is reduced to Ce3+. In addition, the degree of protonation of polyaniline obtained from N1s XPS results in cerium dioxide/polyaniline composites is about 48.52%.Sample preparation of CeO2/polyaniline core–shell nanocomposites.
Keywords: Cerium dioxide; Polyaniline; Core–shell nanocomposites
Preparation of Fe-doped mixed crystal TiO2 catalyst and investigation of its sonocatalytic activity during degradation of azo fuchsine under ultrasonic irradiation
by Jun Wang; Wei Sun; Zhaohong Zhang; Zhe Jiang; Xiaofang Wang; Rui Xu; Ronghe Li; Xiangdong Zhang (pp. 202-209).
In this work, Fe-doped mixed crystal TiO2 powder as sonocatalyst was prepared by the sol–gel method and heat treatment, and a novel method combined with ultrasonic irradiation was propounded to degrade the organic polluted water. First, the Fe-doped mixed crystal TiO2 powder was characterized by TG–DTA, XRD, and TEM techniques. Ultrasound was used as the irradiation source and the azo fuchsine was chose as the model compound. Then a series of degradation experiments was carried out in the presence of Fe-doped mixed crystal TiO2 powder. Also, the degradation process and some influencing factors, such as irradiation time, doping Fe3+ ion content, added amount of catalyst, and initial concentration of azo fuchsine solution, on the degradation were investigated by UV–vis spectra, ion chromatography, and HPLC. Through the degradation of azo fuchsine, it was found that the combination of ultrasonic irradiation and Fe-doped mixed crystal TiO2 powder can completely degrade the azo fuchsine in aqueous solution. Because of the good degradation efficiency, this method may be an advisable choice for the treatments of non- or low-transparent wastewaters in the future.
Keywords: Fe-doped mixed crystal TiO; 2; Sol–gel method; Heat treatment; Sonocatalytic degradation; Azo fuchsine
Surface characterisation of chemically reduced electrolytic manganese dioxide
by Aaron P. Malloy; Scott W. Donne (pp. 210-218).
In this work a titration technique has been used to characterize the amphoteric surface properties of a series of chemically reduced electrolytic manganese dioxide (EMD) samples (MnO1.97 to MnO1.50). The surface of the EMD was found to consist of independent acidic and basic hydroxyl groups, which were able to be characterised by their respective equilibrium constants and site concentrations. For this chemically reduced seriesKb varied from(1.81–8.43)×10−10 as reduction proceeded, with the corresponding basic site concentration varying from(0.20–2.50)×10−4 mol/m2 over the pH range considered.Ka was ranged from(1.23–9.23)×10−6 over the reduction range considered. The increase inKb suggested a weakening of the MnO bond via the introduction of the larger Mn3+ ions which will increase the length of this bond. Weakening the MnO bond results in a corresponding strengthening of the OH bond giving the surface hydroxyl group a basic nature which is supported by the increasing basic site concentration. For the samples with an x in MnO x value above 1.71 the total number of acidic sites decreased which supports the increase in the concentration of basic sites; however, below 1.71, the surface concentration of acidic sites increases slightly, which can be rationalised by the fact that the pyrolusite domains within the EMD (with relatively stronger MnO bonds) are accessible at this stage of the reduction. The number of surface oxide sites (Ns) and surface hydroxyl sites ( Ns(OH)) were calculated crystallographically, and from the sum of the acid and basic hydroxyl groups determined by titration. Both methods produced data with the same order of magnitude, as well as indicated the expected increase in the number of surface hydroxyl groups with increasing degree of reduction. Electrochemical analysis of the samples in 9 M KOH showed the expected decrease in capacity with an increase in the degree of reduction. It also showed a decrease in the amount of charge contributed to the overall homogeneous reduction by Mn4+ ions in surface defects and within the ramsdellite domains over the entire x in MnO x range. However, the amount of charge contributed from the pyrolusite domains remained unchanged until after a x in MnO x value of 1.71.A titration technique has been used to characterize the amphoteric behaviour of a range of chemically reduced electrolytic manganese dioxide samples.
Keywords: Manganese dioxide; Surface titrations; Surface hydroxyl groups; Battery materials
Colloid aspects of chemical–mechanical planarization
by E. Matijević; S.V. Babu (pp. 219-237).
The essential parts of interconnects for silicon based logic and memory devices consist of metal wiring (e.g. copper), a barrier metal (Ta, TaN), and of insulation (SiO2, low- k polymer). The deposition of the conducting metal cannot be confined to trenches, resulting in additional coverage of Cu and Ta/TaN on the surface of the dielectrics, yielding an electrically conducting continuous but an uneven surface. The surplus metal must be removed until a perfectly flat surface consisting of electrically isolated metal lines is achieved with no imperfections. This task is accomplished by the chemical–mechanical planarization (CMP) process, in which the wafer is polished with a slurry containing abrasives of finely dispersed particles in submicrometer to nanometer size. The slurries also contain dissolved chemicals to modify the surfaces to be planarized. Eventually the final product must be cleared of any adhered particles and debris left after polishing is completed. Obviously the entire process deals with materials and interactions which are the focal subjects of colloid and surface science, such as the natures of abrasive particles and their stability in the slurry, the properties of various surfaces and their modifications, adhesion and detachment of the particles and different methods for the characterization of constituents, as well as elucidation of the relevant interfacial phenomena. This review endeavors to describe the colloid approach to optimize the materials and processes in order to achieve desirable polish rates and final surfaces with no imperfections. Specifically, the effects of the composition, size, shape, and charge of abrasive particles on the polish process and the quality of planarized wafers is described in detail. Furthermore, the interactions of metal surfaces with oxidizing, chelating, and other species which affect the dissolution and surface modification of metal (copper) surfaces are illustrated and related to the planarization process. Finally, using the packed column technique the adhesion phenomena of abrasives on metals and oxides is evaluated on suitable model systems, that contain the same additives in the slurries as in the actual planarization process. A close correlation is established in all cases between the attachment and detachment results with experimentally determined polish rates.This review describes the uses of uniform particles (abrasives) and colloid chemical methods to develop a better understanding of the chemical–mechanical planarization (CMP) process.
Keywords: Abrasive; Adhesion of particle slurries; Copper dissolution; Planarization; Polishing wafers
Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions
by Gregorio Guadalupe Carbajal Arizaga; Antonio Salvio Mangrich; Fernando Wypych (pp. 238-244).
A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2⋅2H2O) and a layered double hydroxide (Zn/Al–NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (withD3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show theC2v symmetry for the nitrate ion, whereas theg∥/A∥ value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.
Keywords: Layered double hydroxide; Layered hydroxide salt; Intercalation; Electron paramagnetic resonance; Surface chemical modification
SEM analysis and gas permeability test to characterize polysulfone membrane prepared with polyethylene glycol as additive
by B. Chakrabarty; A.K. Ghoshal; M.K. Purkait (pp. 245-253).
Phase inversion method is applied to prepare flat sheet asymmetric polymeric membranes from homogeneous solution of 12 wt% polysulfone (PSf) with two different solvents— N-methyl-2-pyrrolidone (NMP) and dimethyl acetamide (DMAc). 5.0 wt% polyethylene glycol (PEG) of three different molecular weight (400, 6000, and 20,000 Da) is used as the polymeric additives in the casting solution. Membranes are characterized by two different techniques viz. scanning electron microscopy (SEM) and gas permeation tests. Finally, the results of both the techniques are compared with those calculated from pure water permeation tests using Hagen–Poiseuille equation. It is found that though the values obtained from all the techniques vary from each other, their trend with increase in molecular weight of PEG seems to be the same. It is seen that when molecular weight of PEG increases from 400 to 20,000 Da, the mean pore size of the prepared membranes decreases, while the porosity and pore density show an increasing trend; the pressure normalized gas flux rises significantly and the thickness of the top layer of the prepared membrane sheet increases.Flat sheet polysulfone membranes are prepared using NMP as solvent and PEG as additives. Results show that mean pore size of the membranes decreases with the increase in molecular weight of PEG.
Keywords: Polysulfone membrane; Polyethylene glycol; Gas permeability; Pore size distribution; Effective porosity; BSA
Preparation and characterization of nanostructured Ni(OH)2 and NiO thin films by a simple solution growth process
by Q.Y. Li; R.N. Wang; Z.R. Nie; Z.H. Wang; Q. Wei (pp. 254-258).
Nanostructured Ni(OH)2 thin films were prepared by a simple solution growth process with F− and NH3 used as Ni2+ coordination agents, and ammonia hydroxide solution used as OH− supplier to accelerate the hydrolyzation of nickel complex species. The results showed Ni(OH)2 thin films were constructed mainly with hexagonalβ-Ni(OH)2 nanorods; the F− and NH3 in reactive solutions played important roles in the film growth process; and solution pH had great influence on the morphologies of thin films, which was explained by the competition of Ni(OH)2 nucleation and growth in solutions. NiO crystallinity thin films were obtained by annealing Ni(OH)2 thin films at 400 °C for 2 h and the morphologies of the Ni(OH)2 thin films were sustained well during the annealed process.It was unique that Ni(OH)2 films were constructed with Ni(OH)2 nanorods and there were a lot of open pores resulted from the interconnection of the Ni(OH)2 nanorods in the thin films. The film from the SEM cross-sectional view, the thickness of the films synthesized with pH 8.0 was about 550 nm.
Keywords: Ni(OH); 2; NiO; Nanostructure; Thin films
An analytic solution of capillary rise restrained by gravity
by N. Fries; M. Dreyer (pp. 259-263).
We derive an analytic solution for the capillary rise of liquids in a cylindrical tube or a porous medium in terms of height h as a function of time t. The implicitt(h) solution by Washburn is the basis for these calculations and the Lambert W function is used for its mathematical rearrangement. The original equation is derived out of the 1D momentum conservation equation and features viscous and gravity terms. Thus ourh(t) solution, as it includes the gravity term (hydrostatic pressure), enables the calculation of the liquid rise behavior for longer times than the classical Lucas–Washburn equation. Based on the new equation several parameters like the steady state time and the validity of the Lucas–Washburn equation are examined. The results are also discussed in dimensionless form.An extension to the Lucas–Washburn equation validity for longer times is derived.
Keywords: Capillary rise; Capillary tube; Analytic solution; Liquid penetration; Porous medium; Imbibition; Lucas–Washburn equation; Washburn equation; Lambert; W; function
Effective van der Waals surface energy of self-assembled monolayer films having systematically varying degrees of molecular fluorination
by Mitsuru Takenaga; Sadaharu Jo; Michael Graupe; T. Randall Lee (pp. 264-267).
The systematic variation of the van der Waals surface energy with fluorination for a series of self-assembled monolayers (SAMs) generated by the adsorption of partially fluorinated alkanethiols onto the surface of gold is examined experimentally and theoretically. The surface energy is elucidated on the basis of an effective Hamaker constant, which is obtained as a combination of the respective Hamaker constants of fluorocarbons and hydrocarbons; the fraction depends on the degree of fluorination. The good agreement between experiment and theory is discussed. In addition, the Hamaker constants of various liquids contacted on the well-defined hydrophobic surfaces are interpreted using modified Lifshitz theory.
Keywords: Self-assembled monolayer; SAM; Hydrocarbon; Fluorocarbon; Partially fluorinated; Surface energy; Hamaker constant; Lifshitz theory
Interfacial tension of solid materials against dense carbon dioxide
by Y. Sutjiadi-Sia; P. Jaeger; R. Eggers (pp. 268-274).
In the Young equation, only two of the four unknowns are measurable. They are the liquid interfacial tensionσlv and the contact angle θ. To solve this equation, another correlation is required. In solving this equation, a better understanding of the magnitude of the solid interfacial tensionσsv and the solid–liquid interfacial tensionσsl is expected. The possibility of a theoretical estimation of the contact angle θ is sought as an alternative to the experimental method. In this paper, an attempt to calculate the solid interfacial tensionσsv is reported. It is based on the intermolecular interaction which is mathematically described in the parameterΦsl according to Good. The calculatedσsv values for PTFE, steel, and glass surrounded by dense carbon dioxide are verified by comparing those values obtained from aqueous and ethanolic systems. Furthermore, the solid interfacial tensionσsv is also used to forecast the water drop contact angle θ. The calculated values are compared with the experimental measured ones.In this paper, an attempt to solve the Young equation by means of the intermolecular interaction parameterΦsl according to Good and co-workers is presented.
Keywords: Solid interfacial tension; Contact angle; Liquid interfacial tension; Wetting; Molecular interaction parameter; Wettability
Effect of phenol on the aggregation characteristics of an ethylene oxide–propylene oxide triblock copolymer P65 in aqueous solution
by J.P. Mata; P.R. Majhi; O. Kubota; A. Khanal; K. Nakashima; P. Bahadur (pp. 275-282).
The effects of phenol on the micellization, micellar growth, and phase separation of a poly(ethylene oxide)- block-poly(propylene oxide)- block-poly(ethylene oxide) (PEO–PPO–PEO) amphiphilic copolymer (Pluronic P65: EO19PO30EO19) in aqueous solution have been studied by cloud point, viscosity, dynamic light scattering (DLS), differential scanning calorimetry (DSC), fluorescence spectroscopy, and small-angle neutron scattering (SANS). Various concentrations of P65 have been chosen to estimate the effect of phenol on different concentration regions of P65. Phenol interacts quite differently at low concentrations (0–2%) than at high concentrations (2–10%) of P65, as per the observation that phenol is more predominant at smaller concentrations of P65. A marked decrease in the cloud points of the P65 solutions is observed in presence of phenol. The critical micelle temperature (CMT) of P65 shows a synergistic effect of phenol on P65 aggregates. Micellar transitions, phase separation, and aggregation behaviours like micellization and micellar growth in the presence of phenol have been observed by combining viscometry, DLS, DSC, and CP. DLS shows that the effect of phenol is predominant at high temperatures. SANS shows a high increase in axial ratio and aggregation numbers in the presence of phenol at fixed concentrations of P65. Fluorescence data illustrate that addition of phenol makes micelles polar but at the same time its favours aggregation. Water-soluble phenol (present in low concentrations) forms aggregates with P65, which can be separated by cloud point extraction, making this study interesting for separation of phenol from the phenol–water system.Cloud points of P65 block copolymer as a function of added phenol concentration: (●) 0.00%, (□) 0.30%, (▴) 0.50%, (◊) 0.80%, and (■) 1.00%.
Keywords: Pluronics; Phenol; Micellar aggregates; Cloud point extraction; DSC; Fluorescence spectroscopy
Phase behavior studies of quaternary systems containing N-lauroyl- N-methylglucamide/alcohol/alkane/water
by Xiaodeng Yang; Hongliang Li; Jinling Chai; Yanhong Gao; Jingfei Chen; Anjing Lou (pp. 283-289).
The three-phase behavior of quaternary systems comprising N-lauroyl- N-methylglucamide (MEGA-12)/alcohol/alkane/water has been studied usingε–β fishlike phase diagrams. From theε–β fishlike phase diagrams a series of phase inversions Winsor I (2) → III (3) → II (2¯) were observed, and the hydrophilic–lipophilic balanced (HLB) plane equation for the quaternary system was deduced. Some physicochemical parameters, such as the mass fraction of alcohol in the HLB interfacial layer,AS, the coordinates of the start (βB,εB) and end points (βE,εE) of the middle-phase microemulsion, the mass fractions of MEGA-12 and alcohol in the total system (CS andCA), and the solubilities of MEGA-12 and alcohol in oil phase (SO andAO), were calculated. The effects of different alcohols, alkanes, and NaCl concentrations in the aqueous phase on the phase behavior and solubilization capacity were investigated, which indicates that alcohol with longer and alkane with shorter hydrocarbon chains have a larger solubilization capacity. NaCl concentration has little influence on the phase behavior.Phase behavior of quaternary systems formed from N-lauroyl- N-methylglucamide (MEGA-12)/alcohol/alkane/water was studied in terms of fishlike phase diagrams.
Keywords: Microemulsion; Phase behavior; Solubilization capacity; N; -lauroyl-; N; -methylglucamide
Rheological behavior of surfactant-based precursors of silica mesoporous materials
by L.D. Mendoza; M. Rabelero; J.I. Escalante; E.R. Macías; A. González-Álvarez; F. Bautista; J.F.A. Soltero; J.E. Puig (pp. 290-297).
The linear and non-linear viscoelastic behaviors of polymer-like micellar solutions of cetyltrimethylammonium tosilate (CTAT) with added NaOH and tetraethyl orthosilicate (TEOS) to produce precursors of mesoporous materials are studied. The effect of TEOS/CTAT (T/C) ratio at fixed CTAT concentration, CTAT concentration at fixed T/C and aging time are reported. The systems show increasingly larger deviations from near-Maxwell behavior upon increasing T/C ratio, CTAT concentration and aging. Moreover, in steady and unsteady shear-flow, shear banding develops between two critical shear rates, which tend to fade as the T/C ratio and aging increase. The Granek–Cates model is employed to analyze linear viscoelastic behavior. The Bautista–Manero–Puig (BMP) model is used here to reproduce the steady and transient nonlinear rheology of these systems. We explain these results in terms of the changes in inter-macromolecular interactions that arise out of the presence of colloidal additives in the viscoelastic gel. The ordered mesoporous materials were identified by X-ray diffractometry (XRD) and high-resolution transmission electron microscopy.Micellar solutions to produce precursors of mesoporous materials are studied as function of TEOS/CTAT ratio, [CTAT] and aging time. Increasing the study parameters result into fading out of shear banding flow.
Keywords: Polymer-like micelles; Colloidal additives; Inter-macromolecular interactions; Viscoelastic behavior
Solubilization kinetics for polycyclic aromatic hydrocarbons transferring from a non-aqueous phase liquid to non-ionic surfactant solutions
by Letícia A. Bernardez; Subhasis Ghoshal (pp. 298-306).
A modified rotating disk apparatus was used to investigate the mass transfer of two polycyclic aromatic hydrocarbon (PAH) compounds, naphthalene and phenanthrene from a synthesized non-aqueous phase liquid (NAPL) comprised of hexadecane and the 2 PAHs into different non-ionic surfactant solutions. Major factors influencing the rate of solubilization of PAHs from a NAPL in micelles of different non-ionic surfactants were determined. As the surfactant concentration increased, the mass transfer coefficients for both PAHs from the NAPL decreased. The maximum rates of solubilization of the PAHs however increase with surfactant dose. The rate of solubilization was found to be limited by rates of desorption of mixed micelles from the NAPL and their rate of diffusion into the bulk solution phase. The influence of the surfactant molecular structure on the kinetics of the solubilization process was investigated. The results suggested that the length of the alkyl portion of the non-ionic surfactant and the micelle volume influenced the solubilization kinetics. The results of the investigation improve our ability to provide a rational basis for selecting the optimum surfactant and dose to enhance the solubilization of PAHs from NAPLs.Major factors influencing the rate of solubilization of PAHs from NAPL in micelles of non-ionic surfactants were determined using a modified rotating disk apparatus.
Keywords: Kinetics; Solubilization; PAHs; Surfactants; Rotating disk
Effect of addition of dendritic C60 amphiphiles on the structure of cationic surfactant solutions
by Hongguang Li; Changcheng Liu; Jingcheng Hao; Andreas Hirsch (pp. 307-314).
The aggregation behavior of two water-soluble carboxylic C60 derivatives, dendritic methano fullerene octadeca acid (1) and ennea acid (2), in aqueous solutions was investigated. Both1 and2 were highly soluble in pure water and buffer solutions with pH ⩾7.0. Their spectral properties, especially those in the visible region, were found to be influenced greatly by solution parameters and additives. In pure water, dynamic laser light scattering (DLS) measurements revealed that both1 and2 could form aggregates. When1 or2 was added to micelle solution of a cationic surfactant, tetradecyltrimethylammonium hydroxide (TTAOH), unilamellar vesicles with diameters of several hundreds of nanometers were detected by freeze–fracture transmission electron microscope and DLS both below and above the critical micellar concentration of TTAOH. Vesicle formation was greatly suppressed when1 or2 was added to tetradecyltrimethylammonium bromide micelle solution and no vesicles were detected for1 or2 mixed with the aqueous solutions of tetrabutylammonium hydroxide or tetramethylammonium hydroxide, indicating that counterions and the hydrophobic chain length of the cationic surfactants played important roles in vesicle formation. At the same time, for mixtures of1 and2 with anionic surfactant sodium dodecyl sulfate, no vesicles were detected. In highly concentrated NaCl solutions, it was found that1 and2 could also form vesicles, which could be due to the shielding of the electrostatic interactions among hydrophilic parts of1 and2.Added dendritic C60-amphiphiles convert aqueous cationic surfactant micelles into vesicles.
Keywords: Water-soluble carboxylic C; 60; derivatives; Vesicles; Laser light scattering; Freeze–fracture transmission electron microscope
Aqueous behaviour of cationic surfactants containing a cleavable group
by Austin Samakande; Radhouane Chaghi; Gaelle Derrien; Clarence Charnay; Patrice C. Hartmann (pp. 315-320).
The aggregation behaviour of two novel cationic RAFT agents (transfer surfactants);N,N-dimethyl- N-(4-(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium bromide (PCDBAB) and N-(4-((((dodecylthio)-carbonothioyl)thio)methyl)benzyl)-N,N-dimethylethanammonium bromide (DCTBAB) in diluted solutions have been investigated by surface tension, conductimetry and microcalorimetry measurements. The thermodynamic parameters i.e. the critical micelle concentration (cmc), the degree of micelle ionization ( α), the head group surface area (a0),ΔHmic,ΔGmic andTΔSmic are reported at 303 K. The thermodynamic parameters have been compared to those of the conventional surfactant cetyltrimethylammonium bromide (CTAB) in order to specify structural relationships. The obtained results have been discussed considering the hydrophobic behaviour of the SCS linkage and the specific interactions that arise from the introduction of the benzene ring into the hydrophobic part.Two cationic RAFT agents (transfer surfactants) have been synthesized and their aggregation behaviour has been investigated in diluted solutions by surface tension, conductimetry and microcalorimetry measurements.
Keywords: Cleavable cationic surfactant; RAFT agent; Transurf surfactant; Dithio-group-containing surfactant; Micellisation properties; Thermodynamic of micellization process; Free radical polymerization
Parametrical studies of electroosmotic transport characteristics in submicrometer channels
by T. Postler; Z. Slouka; M. Svoboda; M. Přibyl; D. Šnita (pp. 321-332).
Spatially two-dimensional nonequilibrium mathematical model describing electroosmotic flow through a submicrometer channel with an electric charge fixed on the channel walls is presented. This system is governed by the hydrodynamic, electrostatic, and mass transport phenomena. The model is based on the coupled mass balances, Poisson, Navier–Stokes, and Nernst–Planck equations. Nonslip boundary conditions are employed. The effect of an imposed electric field on the system behavior is studied by means of a numerical analysis of the model equations. We have obtained the following findings. If the channel width is comparable to the thickness of the electric double layer, the system behaves as an ion-exchange membrane and the dependence of the electric current passing through the channel on the applied voltage is strongly nonlinear. In the case of negatively (positively) charged walls, a narrow region of very low conductivity (so-called ionic gate) is formed in the free electrolyte near the channel entry facing the anode (cathode) side. For a wide channel, the electric current is proportional to the applied voltage and the velocity of electrokinetic flow is linearly proportional to the electric field strength. Complex hydrodynamics (eddy formation and existence of ionic gates) is the most interesting characteristics of the studied system. Hence, current–voltage and velocity–voltage curves and the corresponding spatial distributions of the model variables at selected points are studied and described in detail.Spatially 2D mathematical model describing the electroosmotic flow through a charged submicron channel is presented. The nonslip boundary conditions are employed. Complex hydrodynamics (eddies formation and existence of ionic gates) is the most interesting characteristics of the studied system. The current–voltage and velocity–voltage curves, and corresponding spatial distributions of model variables are described in detail.
Keywords: DC electroosmosis; Submicrometer channel; Mathematical modeling; Nonequilibrium model; Complex hydrodynamics
Pd–Pt and Fe–Ni nanoparticles formed by covalent molecular assembly in supercritical carbon dioxide
by Sreenivasa Reddy Puniredd; Seah Weiyi; M.P. Srinivasan (pp. 333-340).
We report the formation of Pd–Pt nanoparticles within a dendrimer-laden ultrathin film matrix immobilized on a solid support and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide (SCCO2) as the processing medium. Particle size distribution and composition were controlled by precursor composition. The precursor compositions are optimized for Pd–Pt nanoparticles and later extended to the formation of Fe–Ni nanoparticles. As an example of the application of nanoparticles in tribology, Fe–Ni nanoparticle-laden films were observed to exhibit better tribological properties than those containing the monometallic species, thereby suggesting that combination of nanoparticles can be used to derive greater benefits.HRTEM image for the Pd–Pt nanoparticles that are immobilized within the dendrimer layers using supercritical carbon dioxide as the processing medium.
Keywords: Pd–Pt and Fe–Ni nanoparticles; Supercritical carbon dioxide; Dendrimer; Covalent molecular assembly; Tribology
Micelle-assisted synthesis of polyaniline/magnetite nanorods by in situ self-assembly process
by Xuefeng Ding; Dongxue Han; Zhijuan Wang; Xiaoyu Xu; Li Niu; Qiang Zhang (pp. 341-345).
Polyaniline/magnetite nanocomposites consisting of polyaniline (PANI) nanorods surrounded by magnetite nanoparticles were prepared via an in situ self-assembly process in the presence of PANI nanorods. The synthesis is based on the well-known chemical oxidative polymerization of aniline in an acidic environment, with ammonium persulfate (APS) as the oxidant. An organic acid (dodecylbenzenesulfonic acid, DBSA) was used to replace the conventional strong acidic (1 M HCl) environment. Here, dodecylbenzenesulfonic acid is used not only as dopant, but also as surfactant in our reaction system. So, DBSA can excellently control the morphology and size of PANI nanorods and magnetite particles. Magnetite particles were formed simultaneously during sedimentation, and the formed nanorods were also decorated by the particles. The resulting PANI/magnetite composites were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). It is found that PANI/magnetite nanorod composites have uniform size, superparamagnetism and a small mass fraction of magnetite, thermal stabilization even at a higher temperature.Polyaniline/magnetite nanorod composites consisting of polyaniline (PANI) nanorods surrounded by magnetite (Fe3O4) nanoparticles were prepared via an in situ self-assembly process in the presence of PANI nanorods.
Keywords: Magnetic properties; Micelles; Nanorods; Polymerization; Self-assembly
Kinetics of 1,3-dipolar cycloaddition on the surfaces of Au nanoparticles
by Christopher Jay Thode; Mary Elizabeth Williams (pp. 346-352).
Triazole formation via 1,3-dipolar cycloaddition, or “ click” chemistry, is a powerful synthetic method for incorporating chemical functionality onto the surfaces of Au nanoparticles. To investigate the factors that govern azide/alkyne reactivity at particle surfaces, we measured the general kinetic trends for the uncatalyzed reaction using FTIR spectroscopy. This study examines the roles of ligand length, electronic substitution of the alkyne species, and solvent on the reaction under pseudo-first-order conditions. The conversion of azide to triazole is found to depend more strongly on the relative surface coverage of azide terminated alkanethiol than on the ligand length and solvent.The general kinetic trends for the uncatalyzed triazole formation on Au nanoparticle surfaces were measured using FTIR spectroscopy. This study examines the roles of ligand length, electronic substitution of the alkyne species, and solvent on the reaction under pseudo-first-order conditions. The conversion of azide to triazole is found to depend more strongly on the relative surface coverage of azide terminated alkanethiol than on the ligand length and solvent.
Keywords: Nanoparticle; Click chemistry; Rate; FTIR; Azide; Alkyne
Electrical double-layer interaction between oppositely charged dissimilar oxide surfaces with charge regulation and Stern–Grahame layers
by S. Usui (pp. 353-359).
The force of double-layer interaction between dissimilar flat oxide surfaces charged oppositely at infinite separation and with Stern–Grahame layers was calculated as a function of the surface separation under the conditions of charge regulation. The interaction force showed a monotonic attraction with respect to the surface separation, lying between constant surface potential and constant surface charge conditions. The variations of surface potentials and surface charge densities of respective double layers were also presented as functions of the surface separation. When the negative diffuse-layer potential at infinite separation changed its sign to positive as a result of specific adsorption of cations on the negatively changed surface, the double-layer interaction force showed a repulsive force barrier followed by an attraction at some particular separation.Oppositely charged dissimilar double-layer interaction force is always attractive (Fig. 1(1), Fig. 2(1)). When−ψd2 becomes positive due to specific adsorption of cations (Fig. 1(2)) the force shows a repulsive force barrier (Fig. 2(2)).
Keywords: Double-layer interaction; Dissimilar double layer; Oppositely charged; Charge regulation; Oxides; Surface force; Stern–Grahame layer
Blastulae aggregates: New intermediate structures in the micelle-to-vesicle transition of catanionic systems
by N. Vlachy; A. Renoncourt; M. Drechsler; J.-M. Verbavatz; D. Touraud; W. Kunz (pp. 360-363).
A new type of intermediate structure was found in the salt-induced micelle-to-vesicle transition in a catanionic system composed of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in aqueous solution with an excess of anionic surfactant. The appearance of symmetrically shaped hollow structures, which we named blastulae vesicles, is presented.The formation of symmetrically shaped intermediate structures, i.e. blastulae vesicles, in non-equimolar catanionic systems.
Keywords: Blastulae; Catanionics; Vesicles; Salt effects