Effect of Cationic Surfactants on the Conformational Transition of Poly(methacrylic acid)

Article abstract of DOI:10.1021/ja00280a026

The interaction between poly(methacrylic acid) and alkyltrimethylammonium bromide, C_nTAB, cationic surfactants has been investigated in aqueous solutions of pH 8, by use of the photophysics of pyrene and its derivatives.Photophysical studies of these fluorescent probes, both steady-state and pulsed laser studies, show that a conformational transition of PMA is induced by C_nTAB.The surfactant induces a coiling up of PMA chains at pH 8, which takes place via a cooperative process.This effect takes places when the concentration of C_nTAB is above a critical aggregate concentration, CAC.The CAC is 1 or 2 orders of magnitude less than the cmc of the corresponding micelle.There is a significant effect of surfactant chain length and PMA concentration on the CAC, which provides information on the nature of the CAC and the mechanism of the PMA transition.A model is suggested for the aggregation of PMA-C₁₀TAB based on experimental data.Studies show that the aggregate consists of about 100 C₁₀TAB molecules and 1 coiled polymer chain.