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The course of dispersion polymerization of aniline using ammonium peroxodisulfate (APS) as initiator oxidant and poly(vinyl alcohol) as stabilizer in different media, viz., water (1 M HCl), water (pH ) 2.41, [aniline] ≡ [HCl]), and aqueous ethanol (1 M HCl), was followed spectrophotometrically. It was found that the absorption peak positions for the pernigraniline salt change markedly with change in acidity and [APS]/[aniline] ratio. The spectral shape also changes greatly when water is replaced by aqueous ethanol. The evolution of the spectra with time was used to generate rate curves which reveal the autocatalytic nature of the reaction. The activation energies of the reaction in the various media were evaluated for both the induction period and the polymerization period using the inverse of the times of these periods as representing average rates for the periods, respectively. The activation energies increase with decrease in medium polarity and/or acidity. These variations have been discussed.

Thermoresponsive gold nanoparticles (GNPs) have been prepared by the borohydride reduction of gold salt in the presence of water-soluble polymer, poly(vinyl methyl ether) (PVME). The PVME-coated GNPs (PVME-GNPs) have been assembled into large aggregates in the presence of polyelectrolytes, viz., poly(sodium-4 styrene sulfonate) and sodium salt of carboxymethylcellulose at low pH by raising the solution temperature from 20 to 40 degrees C. Increase of temperature triggers the interparticle association due to hydrophobic interaction of pendent methyl group of the surface adsorbed PVME. This assembly process is reversible with respect to temperature and pH of the medium and was studied by monitoring the change in surface plasmon resonance band of PVME-GNPs. Three-dimensional assemblies of various architectures, depending on the concentration of polyelectrolytes, were observed through transmission electron microscopy. A mechanistic model has been suggested for the reversible assembly formation that suits well with the experimental observations. The changes in optical properties of the PVME-GNPs due to their aggregation/disaggregation enabled us to use it as an effective tool to monitor the change in lower critical solution temperature (LCST) of PVME in the presence of polyelectrolytes due to interpolymer complexation at low pH. This result agrees well with the variation of LCST of pure aqueous PVME solution in the presence of polyelectrolytes measured by conventional turbidimetric technique.

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