Effect of alkyl chain length on the adsorption and frictional behaviour of 1-alkyl-3-methylimidazolium chloride ionic liquid surfactants on gold surfaces

A study comprising the adsorption and frictional behaviour of 1-alkyl-3-methylimidazolium chloride ionic liquids, [Cnmim][Cl] (with n = 10,12,14), deposited on gold surfaces at a fixed concentration of 0.07 M was carried out using a quartz crystal microbalance (QCM), a nanotribometer and an atomic-force microscope (AFM). The size of the alkyl side-chain of the cation and the corresponding adsorption and frictional results correlate quite well. AFM morphological images support the reasoning put forward for the observed trends. They also suggest that the alkyl chain length of the cation plays an important role in the definition of the structure of the adsorbed aggregates. The ratio between the working concentrations and the critical micelle concentration of the studied ionic liquids is also an important factor.