EFFECT OF EO CHAIN-LENGTH OF DODECANOL ETHOXYLATES (C(12)E(N)) ON THECOMPLEXATION OF C(12)E(N) SDS MIXED MICELLES WITH AN OPPOSITELY CHARGED POLYELECTROLYTE/

Turbidimetry, dynamic light scattering, and capillary electrophoresis were used to study the complexation of polydiallyldimethylammonium chl oride (PDADMAC) with mixed micelles of sodium dodecyl sulfate (SDS) an d dodecanol ethoxylates (C(12)E(n)). The effect of EO chain length and its distribution was examined using various combinations of C(12)E(n) (n = 4, 6, 8, 12). The results show that the onset of the complexatio n of PDADMAC with the mixed micelles is affected by the EO chain lengt h of C(12)E(n): the mole fraction (Y) of SDS in the mixed micelle requ ired to form the complex (Y-c) increases with n. The effect of EO chai n length on the onset of bulk phase separation shows the same trend. A lthough Y-c varies with n, the electrophoretic mobility of mixed micel les with composition corresponding to Y-c is independent of n. We prop ose that the effect of EO chain length has two aspects: (1) an increas e in the average distance between bound polycation segments and the SD S sulfate groups, and (2) an increase in the distance between SDS head groups, which causes a decrease in the surface charge density (sigma) of the micelle. Therefore, the electrical potential at the mean locus of bound polymer segments, psi(0), decreases with increasing n; in or der for complexation to occur, this effect must be compensated for by a larger value of Y. Broader distributions of EO chain length lead to an increase in the range of Y over which the soluble complex is stable . We suggest that polycations initially bind to micelles which are ric h in shorter EO chains and thus have higher ''surface'' potential, psi (0). However, additional SDS may go preferentially into micelles rich in longer chains with lower psi(0). This delays the formation of micel les which have sufficiently large psi(0) to cause phase separation. (C ) 1996 Academic Press, Inc.