Interaction between cationic surfactants and poly(vinyl alcohol)

Abstract

The binding of four cationic surfactants (tetradecylpyridinium chloride and bromide, dodecylpyridinium chloride and dodecylammonium chloride) to poly (vinyl alcohol) (10% acetylated) was measured in aqueous solution by potentiometry using a surfactant-selective electrode and complementarily by equilibrium dialysis. The amount of binding was very small at low equilibruim concentrations ( C f), but increased markedly as the C f approached the critical micelle concentration (c.m.c) of each surfactant. By comparing the effect of cationic head groups, counter-ion, and alkyl chain length at low C f, it was inferred that the alkyl chain plays a minor role, while the polar head groups, especially a monoalkylammonium group, contribute very much to the binding affinity. As for the effect of added electrolyte, it was very little at low C f, but at higher C f binding increased sharply near the c.m.c. The amount of binding was replotted against a reduced equilibrium concentration, C f/c.m.c. and then all the binding isotherms came together on a single isotherm showing that ordinary micellization has an intimate connection with the binding at higher C f.