Interactions between carboxymethyl cellulose and cationic surfactants 1. Phase equilibria and surface tensions

The surface tensions and phase equilibria of carboxymethyl cellulose (CMC)/surfactant/water systems were investigated as a function of the charge density of the polymer, the chain length of the surfactants and the ionic strength. No interactions were observed between CMC and non-ionic surfactants. In systems of CMC and cationic surfactants (tetraalkylammonium bromides) critical association concentrations are observed at concentrations well below the critical micelle concentrations of the surfactants. Associative phase separation occurs in extremely dilute systems when the charge ratio between the surfactants and the polymers is close to zero. The separated phase is a viscous gel phase containing 40-60% of water. The properties of the systems can be qualitatively understood assuming that (a) the driving force for association of the surfactants with the polysaccharide chains increases as the hydrophobic chain length of the surfactant or the charge density of the polyelectrolyte increases, and (b) there is an associative interaction between the surfactant aggregates and the polysaccharide which decreases with increasing ionic strength.