Aggregation numbers of hydrophobic microdomains formed from poly(dimethyldiallylammonium-co-methyl-n-dodecyldiallylammonium) salts in aqueous solutions

This paper provides a comparison of the solution properties in water of surfactants and polysoaps of closely related chemical structures. The main emphasis is placed on mean aggregation numbers (N) and how these values are affected by the nature of the counterions. The techniques used were steady-state fluorescence quenching and NMR spectroscopy. The aromatic counterions benzoate (Ben) and salicylate (Sal) bind very efficiently to micelles formed from methyl-n-dodecyldiallylammonium (MDDA) salts. H-1 NMR spectroscopic data show that these counterions are incorporated into the palisade layer, which most likely accounts for the observed efficiency of binding, Mean aggregation numbers of MDDA micelles with chloride, bromide, and benzoate counterions were determined using steady-state fluorescence quenching, It was found that N decreases in the order MDDAB approximate to MDDABen > MDDAC. The results for these micelles are of immediate relevance for understanding counterion effects on the formation of microdomains in aqueous solutions of the structurally related poly(dimethyldiallylammonium-co-methyl-n-dodecyldiallylammonium) salts, Copol C1-12 90/10 X(X = chloride, bromide, and benzoate). The ratio n/m indicates the relative amount of dimethyldiallylammonium monomer incorporated in the polymer relative to the methyl-n-dodecyldiallylammonium monomer, N values were measured for the microdomains formed from these polysoaps in aqueous solutions, Again, N decreases in the order Copol C1-12 90/10 Ben greater than or equal to Br > Cl. Thus, evidence is provided that headgroup repulsion is a main factor which opposes growth of the microdomains. Addition of salt to Copol microdomains did not significantly influence the size of the domains, Interestingly, the mean aggregation number of Copol C1-12 n/m Cl microdomains did not change with an increasing number of n-dodecyl chains per polymer molecule when n/m > 98/2. (C) 1996 Academic Press, Inc.