COMPLEX-FORMATION BETWEEN POLYELECTROLYTE AND OPPOSITELY CHARGED MIXED MICELLES - SOLUBLE COMPLEXES VS COACERVATION

The system comprised of poly(dimethyldiallylammonium chloride) (PDMDAA C) and oppositely charged mixed micelles of triton X-100 (TX100) and s odium dodecylsulfate (SDS) displays several states, including coacerva te and various soluble complexes. The phase boundary for the equilibri um between soluble complexes and coacervate (''associative phase separ ation'' according to Piculell and Lindman) for 0.4 M NaCl and Y = [SDS ]/([SDS] + [TX100]) = 0.3 was constructed. Coacervation takes place wh en the total concentration of surfactants and PDMDAAC is very low and the weight ratio of PDMDAAC to TX100-SDS, W, is close to 0.09, a stoic hiometry which corresponds to a 1:1 charge ratio of PDMDAAC to TX100-S DS. The phase separation region region is over 2 orders of magnitude s maller than that of most polyelectrolyte/ oppositely charged surfactan t systems (without nonionic surfactant). In the soluble complex region , dilution with 0.4 M NaCl is seen to disaggregate multipolymer comple xes into intrapolymer complexes, but the electrophoretic mobility of t he complexes remains unchanged. The electrophoretic mobility of comple xes changes from negative to positive with increasing W and approaches zero at incipient coacervation. In the soluble complex region, an inc rease in W leads to an increase in the concentration of intrapolymer c omplexes, followed by formation of interpolymer complexes and coacerva tion. Further increase in W redissolves the coacervate. The formation of soluble complexes over a wide range of conditions supports the theo retical models of complex coacervation by Veis and by Tainaka. However , the interpolymer complex formation that is observed in this system i s not considered in either theory.