Syed Qutubuddin

Polymer-clay nanocomposites: exfoliation of organophilic montmorillonite nanolayers in polystyrene

Abstract A polymerizable cationic surfactant, vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for functionalization of montmorillonite (MMT) and preparation of exfoliated polystyrene–clay nanocomposites. Organophilic MMT was prepared by cationic exchange between inorganic ions of MMT and ammonium cations of VDAC in an aqueous medium. Dispersions of intercalated clay (VDAC–MMT) in styrene monomer formed gels. Shear thinning behavior of the gels was observed via rheological measurements. Polystyrene–clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed organophilic MMT. Exfoliation of MMT in polystyrene matrix was achieved as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exfoliated nanocomposites have higher dynamic modulus and higher decomposition temperature than pure polystyrene.

Synthesis of polystyrene-clay nanocomposites

A reactive cationic surfactant vinylbenzyldimethyldodecylammonium chloride (VDAC) was synthesized for intercalation of montmorillonite (MMT), a smectic type of clay. Organophilic MMT was prepared by ion exchange between Na+ ions in the clay and VDAC cations in aqueous medium. VDAC-intercalated MMT particles were easily dispersed and swollen in styrene monomer. Polystyrene–clay nanocomposites were prepared by free radical polymerization of styrene containing dispersed clay. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that exfoliation of MMT was achieved. Polystyrene–clay nanocomposites have higher dynamic modulus than pure polystyrene (PS).

Electrochemically synthesized polypyrrole films: effects of polymerization potential and electrolyte type

Polypyrrole films containing either the perchlorate or p-toluenesulfonate ion were prepared from an aqueous solution by applying an anodic potential in the range 0.6–2.0 V (relative to a saturated calomel electrode). The effects of applied potential on electropolymerization, morphology, chemical structure, electrochemical properties and tensile modulus have been investigated. The chronoamperometric response of pyrrole electropolymerization depends on the applied potential and not on the counterion. The electrochemical properties and structure of polypyrrole depend on the polymerization potential as well as the counterion. An empirical expression relating peak current to the scan rate and charge passed during polymerization is proposed. This relationship provides some insight into the nature of the polypyrrole switching reaction. For polypyrrole containing perchlorate, the concentration of dicationic species or dipolarons decreases as the polymerization potential increases from 0.6 to 1.0 V. The large concentration of dicationic species in polypyrrole prepared at 0.6 and 0.75 V is responsible for the second reduction peak observed in the cyclic voltammograms.

Poly(vinyl alcohol) hydrogels: 2. Effects of processing parameters on structure and properties

Abstract Poly(vinyl alcohol) (PVA) hydrogels were prepared by quenching solutions containing PVA polymer in pure water or an aqueous solution of dimethylsulfoxide (DMSO). Remarkably different PVA hydrogels were obtained by varying processing parameters, i.e. DMSO concentration, initial PVA concentration and quench temperature. The bulk structure of PVA hydrogels was investigated by scanning electron microscopy of samples prepared by freeze-etching. Physical and mechanical properties of the hydrogels were evaluated to determine the effects of the processing parameters. The experiments were planned according to the Box-Behnken design for surface response. PVA hydrogels prepared at low quench temperature using high DMSO and PVA concentrations exhibit low water content and significantly improved hardness, tensile strength, elongation and tear resistance strength. The best mechanical properties are obtained at the maximum DMSO concentration investigated, 75 wt%. The optical transparency of PVA hydrogels is optimized for samples prepared using 75 wt% DMSO solution containing 8 to 9 wt% PVA at a quench temperature between −20 and −35°C. An increase in DMSO and/or PVA concentrations leads to a more homogeneous and denser hydrogel structure with significantly lower equilibrium swelling. The presence of DMSO-water complexes in the medium alters the gelation mechanism and causes differences in hydrogel structure and properties.

Electrochemical investigation of microemulsions

Abstract Two electrochemical techniques, cyclic voltammetry and rotating disk voltammetry, were successfully applied to characterize oil-in-water microemulsions. Diffusion coefficients of microemulsion droplets were determined using ferrocene as the hydrophobic electroactive probe. Microemulsions containing n-octane as the oil, cetyltrimethylammonium bromide as the surfactant, n-butanol as the cosurfactant, and NaBr as the electrolyte were investigated. The diffusion coefficients are compared with values obtained from quasielastic light scattering measurements. The differences observed between electrochemical and light scattering measurements are due to the different modes of diffusion probed by these techniques. The electrochemical techniques yield values of the self-diffusion coefficients, whereas light scattering techniques yield mutual-diffusion coefficients. The diffusion coefficients are strongly affected by interactions between the microemulsion droplets. Compared to light scattering, the electrochemical approach provides a faster and less expensive tool for characterizing microemulsions. Electrochemical techniques do not require any prior information of physical properties except viscosity, and are also applicable to opaque systems.

Synthesis of titania-coated silica nanoparticles using a nonionic water-in-oil microemulsion

Abstract Titania-coated silica nanoparticles were prepared by controlled hydrolysis of tetraethoxysilane (TEOS) and titanium n-butoxide (TBOT) in Triton X-45/cyclohexane H2O reverse (water-in-oil) microemulsions. The pH of the microemulsion plays a key role in the coating of titania (TiO2) on silica (SiO2) nanoparticles. TiO2 loading up to 10 wt.% on SiO2 nanoparticles was detected by SEM-EDS. Quasielastic light scattering and transmission electron microscopy were used to characterize the size and morphology of synthesized nanoparticles.

Influence of electrolyte and polymer loadings on mechanical properties of clay aerogels.

The effects of electrolyte and polymer loadings on formation, density, and mechanical properties of clay aerogels have been investigated. Coherent aerogels were formed at all tested concentrations except at a combination of low electrolyte (<0.04 M) and polymer (<1% w/v) concentrations because of partial clay flocculation. The compressive modulus and yield strength of the aerogels containing poly(vinyl alcohol) are sensitive to electrolyte loading at low polymer concentration but are otherwise insensitive. Mechanical properties show power law dependence on aerogel density, which depends mainly on polymer loading. The power law exponent for the compressive modulus is 3.74 when the relative density is used in the model and 5.7 when the measured bulk density is used instead. These high exponent values are attributed to the layered microstructure of these aerogels.

Biobased Chitosan/Polybenzoxazine Cross-Linked Films: Preparation in Aqueous Media and Synergistic Improvements in Thermal and Mechanical Properties

A novel class of polymer blends has been prepared from main-chain-type benzoxazine polymer (MCBP) and chitosan (CTS), a modified biomacromolecule. A water-soluble, main-chain-type benzoxazine polymer, MCBP(BA-tepa), was synthesized from the reaction of bisphenol A (BA), tetraethylenepentamine (TEPA) and formalin. The structure of the MCBP(BA-tepa) was confirmed by proton nuclear magnetic resonance spectroscopy ((1)H NMR) and Fourier transform infrared spectroscopy (FT-IR). The polymer blends were prepared by mixing MCBP(BA-tepa) and CTS in aqueous acetic acid solution (1%). The CTS/MCBP(BA-tepa) films are cross-linked by thermal treatment via the ring-opening polymerization of benzoxazine structures in the main chain to produce an AB-cross-linked network. Differential scanning calorimetry (DSC) and FT-IR were used to study the effects of CTS on the polymerization behavior of benzoxazine. Hydrogen bonding between polybenzoxazine and CTS structures was also observed. The mechanical and thermal properties of cross-linked CTS/MCBP(BA-tepa) films were evaluated, and the results showed unusual levels of synergism. In particular, the tensile strength and thermal stability were significantly enhanced in a nonlinear fashion.

Synthesis of titania-coated silica nanoparticles using ono-ionic water-in-oil

Abstract Titania (TiO 2 ) nanocoating on silica (SiO 2 ) particles was obtained by controlled hydrolysis of titanium alkoxide precursors. Monodisperse spherical silica particles prepared by Stober method were used as the support. Isolated silica particles with uniform titania nanocoating were obtained by reacting appropriate alkoxide and water at ambient temperature. The thickness and uniformity of TiO 2 coating were controlled by adjusting the concentrations of reactants and the amount of added SiO 2 . The samples were characterized using electron microscopy and electrophoresis. The surface coverage was estimated using isoelectric point (IEP) data.

Controlled Release in Transdermal Pressure Sensitive Adhesives using Organosilicate Nanocomposites

Polydimethyl siloxane (PDMS) based pressure sensitive adhesives (PSA) incorporating organo-clays at different loadings were fabricated via solution casting. Partially exfoliated nanocomposites were obtained for the hydroxyl terminated PDMS in ethyl acetate solvent as determined by X-ray diffraction and atomic force microscopy. Drug release studies showed that the initial burst release was substantially reduced and the drug release could be controlled by the addition of organo-clay. Shear strength and shear adhesion failure temperature (SAFT) measurements indicated substantial improvement in adhesive properties of the PSA nanocomposite adhesives. Shear strength showed more than 200% improvement at the lower clay loadings and the SAFT increased by about 21% due to the reinforcement provided by the nano-dispersed clay platelets. It was found that by optimizing the level of the organosilicate additive to the polymer matrix, superior control over drug release kinetics and simultaneous improvements in adhesive properties could be attained for a transdermal PSA formulation.