Comparison of aggregation behaviors between ionic liquid-type imidazolium gemini surfactant [C12-4-C12im]Br2 and its monomer [C12mim]Br on silicon wafer.

The aggregation of ionic liquid-type imidazolium gemini surfactant [C12-4-C12im]Br2 on silicon wafer, which is compared with its monomer [C12mim]Br, have been studied. AFM morphology images and contact angle measurements suggest that the aggregations of [C12-4-C12im]Br2 and [C12mim]Br on silicon wafer follow different mechanisms. Below the critical surface aggregation concentrations (CSAC), both surfactant molecules are adsorbed with their hydrophobic tails facing the air. But above the CSAC, [C12-4-C12im]Br2 molecules finally form a bilayer structure with hydrophilic head groups facing the air, whereas [C12mim]Br molecules form a multilayer structure, and with increasing its concentration, the layer numbers increase with the hydrophobic chains and hydrophilic head groups facing the air by turns. Besides, the watery wettability of [C12-4-C12im]Br2-treated silica surface is lower than that of [C12mim]Br at the concentration of 5.0 cmc, and the infrared spectroscopy suggests that the poorer watery wettabili...