Polyelectrolyte chromotropes in metachromacy

Abstract

The chromotropic character of polyacrylic acid and its sodium salt, vinyl acetatemaleic acid copolymer and its sodium salt and the sodium salt of sulphonated polyvinyl alcohol in inducing metachromatic colour change in methylene blue, toluidine blue and crystal violet, has been analysed over a wide range of polymer concentration. The chromotropic behaviour has been associated with the polyelectrolyte character of the molecules. The viscosity measurements of dye-polymer systems have shown that the dye molecules are associated with the polymer chain, which coils up due to partial neutralisation of the charge density on the chain. This brings the adsorbed dye molecules close together to undergo optical superposition, a situation that exists in the polymeric dyes and hence the metachromatic colour change.