Properties of Dilute Aqueous Solutions of Double-Chain Surfactants, Alkyldodecyldimethylammonium Bromides with a Change in the Length of the Alkyl Chains

A series of cationic surfactants, dialkyldimethylammonium bromides with dodecyl as the primary alkyl chain and with methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl as the second alkyl chain, as well as those with symmetric alkyl chains, dioctyl, didecyl and didodecyl ones, were synthesized, and their properties were investigated through measurements of the conductivity and air-liquid surface tension for their aqueous solutions to determine their critical micelle concentrations (cmc) and surface adsorption parameters in the formulation according to a two-dimensional lattice model in the form of the Frumkin equation. The change in cmc revealed that the free energy to transfer from water to the micelle per methylene unit is significantly small for asymmetric double-chain surfactants with a shorter second alkyl chain, and it approaches as elongating the second alkyl to those for the single-chain and symmetric double-chain surfactants. The free energy to transfer to an airsolution interface decreased approximately linearly with the total length of the hydrocarbon chains for all of the species examined. The lattice area for a symmetric double-chain surfactant molecule decreased with the length of its hydrocarbons. In a series of asymmetric ones, it showed a maximum for that with hexyl in its second alkyl.