ALKANEDIYL-ALPHA,OMEGA-BIS(DIMETHYLALKYLAMMONIUM BROMIDE) SURFACTANTS .3. BEHAVIOR AT THE AIR-WATER-INTERFACE

The surface tension of the title compounds, the surfactants CsH2s-alpha,omega-bis(C12H25N+(CH3)2Br-), referred to as 12-s-12,2Br-, has been measured as a function of the surfactant concentration for the homologues with s = 3, 4, 6, 8, 10, 12, 14, and 16. The surface area per surfactant, a, has been obtained by applying Gibbs law to the data in the range from (0.1-0.2)cmc to the cmc. The plot of a va s, spacer carbon number, goes through a maximum for s = 10-12. This behavior is interpreted as reflecting a change of location of the spacer from the interface, in contact with water, to the air side of the interface, at s greater-than-or-equal-to 10 when the spacer becomes sufficiently hydrophobic.