Thin Film Properties of Ammonium Sulfonate Ionic Liquids Having a Long Alkyl Chain

New well-lubricated ILs including ammonium sulfonate having a long alkyl chain have been developed. The materials based on ammonium sulfonate have a higher ΔpKa between the Brønsted acid and the Brønsted base of the salts and do not decompose even at 300 °C, making them more thermally stable than the perfluoropolyether (PFPE). Therefore, octadecyl ammonium sulfonates have a lower frictional coefficient on the carbon overcoat film even after heat treatment at high temperatures. The ILs are adsorbed on the media surface with high orientation. The alkyl chains of the C16 and C18 sulfonates in the bulk have a trans conformation, nevertheless, the films have a gauche conformation. A sufficient length of the hydrocarbon chain leads to both macro and micro-friction reductions. Dimethyl ammonium sulfonate has sufficient solubility in fluorinated solvent, which may make commercial applications possible.