Effects of Simple Electrolytes and Surfactants on the Viscosity of Aqueous Poly(methacrylic acid) Solutions

Abstract

The interaction of poly (methacrylic acid) (PMA) with added salts and surfactants were studied by means of viscometry.
The reduced viscosity of aqueous salt solution of PMA, which is a weak polyelectrolyte, increases rapidly in a highly diluted region and this behavior is contrasted to that of ordinary strong polyelectrolytes. This difference is attributed to the fact that the PMA chain expands with dilution due to the increase of the degree of dissociation of carboxylic group. Salt effect on aqueous PMA solutions was interpreted in terms of dissociation equilibrium of carboxylic group.
In the presence of surfactants, the lowering of reduced viscosity was observed regardless of the properties of hydrophilic parts of surfactants in a highly diluted region of PMA solution. Hydrophobic interaction between PMA and surfactants is predominant and overcomes the effect of dissociation, so that the polymer chain does not expand in low concentration range. Especially in the case of anionic surfactant, in spite of electrostatic repulsion it obviously binds onto the PMA chain judging from the viscosity change and a kind of mixed micelle is formed.