Binding of dodecyloxyethylpyridinium bromide to polymer: the effect of molecular geometry of surfactant

Dodecyloxyethylpyridinium bromide (C₁₂EPB) has been synthesized and compared with the normal N-alkylpyridinium bromides, C_nPB (n=12, 13, 14) to see how the insertion of an oxyethylene group influences the binding behavior to an oppositely charged linear polymer, sodium poly(2-acrylamide-2-methypropanesulfonate) (PAMPS). The geometry factor of surfactant in micellization and in polymer-surfactant interaction are focused on. The oxyethylene group gives a contribution by −1.3 kT to the free energy of micellization and by −1.4 kT to the free energy of binding. The micelle and the cluster of surfactant on polymer are considered to consist roughly of two regions, an outer region containing the ionic headgroup and the first three or four carbons of alkyl chain, and an interior region containing the remaining portions of hydrocarbon chains. The interpositioning of a linkage segment at -position extends the hydrophobic chain in the inner region and favors the surfactant self-association as well as the binding with the oppositely charged polymer.