Evolution in the Supramolecular Complexes between Poly(phenylene ethynylene)-Based Polyelectrolytes and Octadecyltrimethylammonium Bromide as Revealed by Fluorescence Correlation Spectroscopy

Abstract

Poly(phenyleneethynylene)-based conjugated polyelectrolytes (PPE-SO(3)(-)) are a class of polyions with rigid backbones. This work uses fluorescence correlation spectroscopy to study how the diffusion of complexes, formed between a PPE-SO(3)(-) polyelectrolyte and octadecyltrimethylammonium bromide (OTAB) surfactant molecules, changes with OTAB concentration below its critical micelle concentration. The dependence of the hydrodynamic radius of the complexes on the OTAB concentration has three regimes. In the low concentration regime ( C(OTAB)/ C(monomer) < 6), the complex has a size comparable to that of the polymer in deionized water. In the intermediate concentration regime (6 < C(OTAB)/ C(monomer) < 400), the complexes have the largest size and substantial heterogeneity. In the high concentration regime (400 < C(OTAB)/ C(monomer) < 1800), the complexes have a size that is about three times larger than that in the low concentration regime. These results elucidate features of the self-assembly of a polyelectrolyte and an ionic surfactant and show that the C(OTAB)/ C(monomer) concentration ratio controls the composition of polyelectrolyte/surfactant complexes.