Rongshi Cheng

The wall effect on viscosity measurement of dilute aqueous solutions of polyethylene glycol and polyvinyl alcohol using a paraffin-coated capillary viscometer

Abstract The relative viscosities of aqueous solutions of a polyethylene glycol sample and a polyvinyl alcohol sample were measured in a viscometer, the capillary wall surface of which was coated with paraffin. The results were compared with the data obtained from the original non-coated viscometer. Slippage occurs in the former case due to the hydrophobic nature of paraffin, while in the latter case, conventional viscous flow operates since both the solvent water and solution either wet and/or are adsorbed on to the glass capillary surface of the viscometer. The experimental data were analyzed with the aid of the recently proposed theory of the effect of solute adsorption on relative viscosity measurements. The formula, accounting for the effect of solute adsorption of polymer solutions down to the extremely dilute concentration region, are also applicable to non-wetting polymer solutions in which solute adsorption is eliminated. The results obtained were compared and analyzed using the idea of extrapolation length of slip flow proposed by de Gennes PG. CR Acad Sci Paris 1979;288B:219. The extrapolation length could be evaluated unambiguously from the relative or reduced viscosity data for polymer solutions down to the extremely dilute concentration region.

Glass transition temperature of polystyrene microparticles

Abstract Polystyrene (PS) microparticles were prepared by freeze-drying a very dilute cyclohexane solution and by spraying a dilute benzene solution into methanol. D.s.c. studies showed that the microparticles have a transition at a temperature lower than the Tg of bulk PS. This low temperature transition was regarded as the glass transition of the PS microparticles, and it was suggested that the decrease in Tg of the particles was due to their high surface area to volume ratio.

Air-oxidation of gold metal in polybenzimidazole solution

Gold(0) has been found to dissolve in polybenzimidazole solution under extremely mild conditions resulting in a polymeric ‘gel’ with gold(I) and gold(III) cations acting as chain bridging sites.