Pressure-area isotherms for double-chain amphiphiles bearing two hydroxyl groups derived from diepoxides

The pressure-area (pi-A) isotherms for a series of double-chain amphiphiles bearing two hydroxyl groups were measured by the conventional film-balance technique. These double-chain compounds were prepared by reaction of epichlorohydrin with various dihydroxy compounds which become the connecting moiety, followed by reaction of the resultant diepoxides with fatty alcohols. They are synthetic precursors of double-chain surfactants bearing two anionic head groups which have been developed as high-performance ''gemini surfactants'' by the authors' group. The effect of the following factors. on the pi-A isotherms for these compounds was examined: the length of the saturated hydrophobic alkyl chains, the difference between saturated and unsaturated aliphatic chains, temperature, the structure of the connecting group between the two hydrophobic chains, and the difference in configuration of the chiral molecules. Some relationships between the structures of these double-chain amphiphiles and their adsorptive behavior at the air-water interface were clarified: (1) A more tightly packed monolayer was formed as the length of hydrophobic alkyl chain increased and as the length of the alkylene chain of the connecting part was shortened, (2) an unsaturated bond in the middle of the hydrophobic chain contributed to loose packing of the monolayer, (3) the profile of the pi-A isotherms varied with temperature, and (4) no influence of chirality in the molecule on the adsorptive behavior was observed.