Bending of the Flexible Spacer Chain of Gemini Surfactant Induced by Hydrophobic Interaction

In order to understand the special role of the flexible alkylene spacer of gemini surfactant in the self-assembly, three gemini surfactants, alkylene-α,ω-bis(didodecylmethylammonium bromide) that is designated as 2C₁₂-s-2C₁₂· 2Br (s=3, 6, 8), were synthesized. When the spread films of 2C₁₂-s-2C₁₂·2Br on the surface of water were constructed, they form the dense layer of the alkyl tails owing to four dodecyl chains per molecule. This induced the bending of the spacer chain toward the air-side at the s smaller than that of C₁₂-s-C₁₂·2Br adsorbed on the air/water interface owing to the enhanced hydrophobic interaction between the alkyl tails and the spacer chain, where C₁₂-s-C₁₂·2Br has only two alkyl tails per molecule. Conclusively, the enhanced hydrophobic interaction between the alkyl tails and the spacer chain can effectively induce the bending of the latter toward the air-side.