No abstract

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.

The ionic liquid (IL) having a short perfluorether group and a hydroxy group was synthesized newly. The monolayer thickness of the IL and Z-Tetraol (Molecular Weight: approximately 2300) was 1.2 nm and 1.8 nm respectively which is measured by their spreading profiles experimentally. The adhesion and friction force of the lubricant thin film were measured by pin-on-disk microtribotester. While the adhesion force of Z-Tetraol increase with decreasing film thickness, the IL exhibits very small adhesion forces despite high polar energy measured by the contact angle. These adhesion measurement results implied that the interaction between pin and the IL lubricated disk is determined by considering the balance of Van der Walls attraction and electrostatic repulsion.

In order to attain high recording density in a hard disk drive, reduction of the head-media spacing (HMS) is crucial. The contribution of lubricant thickness to the HMS is a significant factor in performance. Because the lubricant thickness is on the order of angstroms, molecules of long-chain lubricants, such as perfluoroether, must lay parallel to the magnetic disk surface to reduce lubricant thickness. In this study, new lubricants were designed using ionic liquids (ILs). The ILs had smaller molecular weight than that of current perfluoropolyether (PFPE) lubricants but with lower evaporation loss. The molecular conformation of the ILs was controlled by two hydroxyl groups, which were placed in a cation moiety at both terminal ends (IL-1) or placed on one side of the cation (IL-2). The monolayer thickness of IL-1 and IL-2 was seen to be 0.6 nm and 1.2 nm, respectively. The adhesion force at a lubricant thickness of 1.0 nm decreased in the order: PFPE (Z-Dol 2000) > IL-2 > IL-1. The small adhesion force, which is one of the essential parameters for low flight of a magnetic head, was achieved by changing the molecular conformation of the IL.