Counterion specificity as the determinant of surfactant aggregation

Abstract

Aggregation numbers and critical micelle concentrations are reported for dodecyltrimethylammonium salts with hydroxide and a range of carboxylates as counterion, with and without added salt. The micelles are unusual in that cmcs are higher and the aggregation numbers and ion binding parameters much lower than those for the corresponding bromides. Aggregation numbers change slowly (29 to 49) with added salt up to 1 M. The micellar properties parallel those of corresponding double-chained dimethylammonium salts which exhibit normal behavior (insoluble, lamellar phase) for bromides and anomalous behavior (highly soluble, spontaneous vesicles) for carboxylates and hydroxide. With increasing surf..