Water adsorption on thin film media

Disk drives experience a wide range of temperature and humidity during stor age and operation. Humidity influences media tribology through the effects of adsorbed water on the interaction of Zdol lubricant hydroxyl end groups with the carbon overcoat, We measured the effects of Zdol 4000 thickness an d chemisorption on the water adsorption isotherm and surface energy. The po tential distortion model of Adamson was employed to derive the film thickne ss at saturation from the isotherms and contact angles. The isotherm was su rprisingly independent of the Zdol chemisorption and thickness up to 1.8 mm , because, in this range of Zdol thickness, the adsorbed water resides in p ores which exclude the larger Zdol end groups. The water adsorption isother m provides a sensitive probe of overcoat structure due the ability of water to reach pores in the overcoat which are inaccessible to Zdol, Above a Zdo l thickness of 1.8 nn there is a jump in the water adsorption as additional adsorption takes place on the "free" hydroxyl groups. The mechanism for th e previously observed decrease in Zdol lubricated media durability at low h umidity is derived from the effect of adsorbed water on Zdol surface diffus ion and chemisorption. (C) 2000 Academic Press.