SURFACE-PROPERTIES, MICELLIZATION, AND PREMICELLAR AGGREGATION OF GEMINI SURFACTANTS WITH RIGID AND FLEXIBLE SPACERS

Micellization and premicellar behavior of the two series of cationic s urfactants, each with two hydrophilic and two hydrophobic groups in th e molecule (''gemini'' surfactants), one series with a rigid, hydropho bic spacer, and second with a flexible, hydrophilic one, have been stu died by use of surface tension measurements. The data show the expecte d regular increase in surface activity with an increase in alkyl chain length for the shorter chain homologs but show increased deviation fr om the regularity with an increase in chain length when the number of carbon atoms in the alkyl chain exceeds a certain number. This deviati on in surface activity appears to be due to the formation of small, no n-surface active aggregates. Equilibrium constants calculated for the aggregation reaction show that the conditions facilitating micelle for mation also favor formation of these premicelles, such as lower temper ature, stronger ionic strength of the solution, and increased alkyl ch ain length. Geminis with a flexible, hydrophilic spacer appear to aggr egate more readily than geminis with a rigid, hydrophobic spacer. Thei r shorter homologs are also more surface active than those having a ri gid, hydrophobic spacer.