Hydrogen bonding in lubricants for hard disk drives

Abstract

Hydrogen bonding interaction within a small ensemble of water molecules, that within a group of water molecules and endgroups of Z-dol and Z-tetraol, and the effect of electrolyte ionic pair such as LiCl upon these interactions were examined by the molecular dynamics method based on the potential given by a semi-empirical SCF quantum mechanics. It was revealed that the strength of the hydrogen bond increased rapidly as the size of droplet increased, relating to the population density of hydroxyl units, and that such interaction was amplified significantly by the presence of electrolyte ionic pair. An extraordinary interaction was thus predicted between Z-tetraol and aqueous solution of alkali halide. An experimental study thence conducted revealed that Z-tetraol and aqueous NaCl solution (2 M) formed an extremely stable water-in-oil type emulsion. The emulsion consists of spheroids of several nanometers across wherein several thousands of water molecules are encased by several tens of Z-tetraol endgroups. The interfacial layer of each spheroid is formed and stabilized by the hydrogen bonding interaction between the hydroxyl units of the tetraol-ends and water molecules enhanced by the electrolyte ionic pairs. When disks coated with Z-tetraol were tested for flyability at high humidity, the head-disk interaction detected acoustically increased with time. Spontaneous formation of globules resulting from interaction of tetraol end-groups and water molecules assisted by ubiquitously present alkali halide contaminant would account for the observed increase of the head-disk interaction. Possible structures of perfluoropolyether lubricants ideal for magnetic disk application are discussed.

Effects of environmental temperature and humidity on thermal flying height adjustment

“…In our opinion, both cases may be correct to a certain extent, depending on the assumptions made in the study. We believe that the complexity of air-bearing systems will cause both cases to happen in reality, that is, as some water molecules interact with the disk and slider surfaces by hydrogen bonding to form a strongly absorbed water film as reported by many researchers Zhao et al 1999;Shukla et al 2002;Kasai and Raman 2006), the others will coalesce to form water droplets because the mean free path of water vapour at standard atmospheric temperature and pressure is estimated to be approximately 50 nm (Kohonen et al 1999;Kaviany 2002), which is comparable to the headdisk spacing. If we define a as the ratio of absorbed water vapour to the condensed one, we can combine Eq.…”

Influence of Microalgal Bio-Oil on the Lubrication Properties of Engine Oil

“…The main reason for this was that, compared with the hydrocarbon chains of traditional lubricating oil such as CD SAE 15W-40, the various polar groups of the bio-oils can form stronger secondary bonds including hydrogen bonds on the friction surfaces [22], which play an important boundary lubrication protection role.…”

Tribological behavior of DLC films in space and automotive oil under boundary lubrication

“…The hydrogen bonding is a weak interaction and it is constantly disrupted by the ambient thermal energy (Kasai, and Raman , 2006). It is well known that there are many polar functional groups on the DLC surface (Yanagisawa, 1994;2001).…”