Murthy Tata

Fluorescence quenching of CdS nanocrystallites in AOT water-in-oil microemulsions

Abstract The luminescence of CdS nanoparticles suspended in “dry” AOT reversed micelles is quite intense but is quenched by water and even more effectively by thiol-containing compounds. Stern-Volmer plots provide information about the quenching efficiencies of various compounds. Of particular interest is 4-hydroxythiophenol which interacts strongly with the surfactant headgroups and thereby partitions to the nanoparticle surface. The quenching efficiency of 4-hydroxythiophenol is more than an order of magnitude greater than that of thiophenol. At the very low concentrations of 4-hydroxythiophenol required to bring about quenching, a remarkable recovery of fluorescence is observed upon continued irradiation. The fluorescence recovery is attributed to photochemical oxidation which consumes the hydroxythiophenol presumably giving a disulfide product.

A spontaneous phase transition from reverse micelles to organogels due to surfactant interactions with specific benzenediols

Abstract Hydrogen-bonding interactions between suitable phenols and the head group of the twin-tailed anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT), form the basis for a novel class of organogels. The gels are novel in that very small quantities of these low molecular weight solutes are sufficient to cause gelation. Previous work has shown that the gel-forming propensity of the phenol is determined by its acid strength and also the substitution pattern on the aromatic ring. Evidence suggests that the underlying molecular architecture of these gels consists of strands of stacked and motionally restricted phenol molecules. The surfactant appears to be linked through hydrogen bonding to the external surface of the stack and its motion is relatively unrestricted. Here, we report the finding that the gels also form with select benzenediols (resorcinol derivatives). Interestingly, these gels are much stronger than some of the strongest gels made with phenols under similar conditions. A combination of NMR and FTIR spectroscopic evidence suggests that these gels derive their strength from binding with both carbonyl groups of the surfactant, whereas in the gels made with phenols, only one carbonyl group is bound. The stacked phenol microstructure of the organogels proposed previously seems to be generally valid for the case of gels formed with the benzenediols. The additional possibility of bridging the adjacent phenol molecules in the stack by the adsorbed surfactant allows for a “scaffolding” around the aromatic stack.

Enzymatic polymerizations using surfactant microstructures and the preparation of polymer-ferrite composites

Horseradish peroxidase has been used as a biocatalyst to synthesize a polymeric material from alkyl-substituted phenols. The synthesis is carried out in a surfactant-based microemulsion environment, with the monomer partitioned at the oil/water interface. The spherical nature of the microemulsion nanodroplets may be acting as a template for the polymer synthesis. The resultant polymer particles are spherical and typically in the submicron size range. The characteristics of the morphology development are described. The templating effect of the surfactant environment becomes more evident when the polymer particles are fully dissolved in a suitable solvent and refolded in the presence of surfactant. Interestingly, submicron-sized spherical particles are obtained only in the presence of surfactant, and particles of arbitrary morphology are seen in the absence of surfactant. Aspects of morphology development leading to the preparation of polymeriron oxide composites are described.

Modifications of CdS nanoparticle characteristics through synthesis in reversed micelles and exposure to enhanced gas pressures and reduced temperatures

Abstract CdS nanoparticles are synthesized in reversed micelles which are then subjected to enhanced pressures of a light hydrocarbon gas. At lower temperatures, clathrate hydrates form, reducing the micellar water content. The particles remain in solution until a critical phase transition pressure. The removal of water leads to an enhancement in particle stability and a resistance to photocorrosion. It is thus possible to prepare CdS particles of various band gap energies and to stabilize these particles subsequently, through a process of water removal and micelle size reduction.

Enzyme-Catalyzed Polymerization in Microstructured Fluid Media: The Synthesis and Characterization of Novel Biomolecular Materials

Phenol-formaldehyde based polymers have widespread use in coatings and adhesive technologiesl. They are used in laminates, wood composites, insulating materials, flame retardants, etc. However, due to the toxicity of formaldehyde, it has become necessary to produce similar polymers that do not involve formaldehyde as an intermediate. The enzymatic synthesis of phenolic polymers is one possible route to such polymers. The feasibility of such synthesis was first demonstrated by Dordick and coworkers2, and later by Akkara and coworkers3 who showed that high molecular weight polymers could be synthesized enzymatically in an organic solvent system containing an 85/15 v/v dioxane/water mixture.