Structure of polymer-surfactant complexes by static light scattering

Light-scattering studies of the structure of macromolecular complexes forme d between poly(ethylene oxide) [PEO] and a cationic surfactant, hexadecyltr imethylammonium chloride [HTAC], in aqueous solution, are reported. Analysi s of the angle dependence of the scattered intensity indicates that binding of HTAC micelles is accompanied by an increase in radius of gyration (R-g) , up to the maximum binding point. From measurements of the molecular weigh t of the PEO-HTAC complex, accounting fur preferential binding of surfactan t, we deduce that, at the maximum binding condition, 0.12 mol of HTAC is bo und per mol of EO. In addition, evaluation of the PEO molecular weight, usi ng equilibrium dialysis, indicates approximately 2.0 +/-0.3 PEO chains are incorporated in the complex. Beyond maximum binding, electrostatic screenin g induces the PEO chain to contract, evidenced by a reduction in R-g. Measu rements of R-g at the maximum binding point for three different PEO molecul ar weights indicate that the relative chain expansion is comparable, R-g,R- complex/R-g,R-PEO similar to 1.9 The results provide insight into earlier o bservations of a viscosity maximum, when titrating dilute solutions of PEO with HTAC.