Fluoroether bonding to carbon overcoats

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Abstract
A set of small fluorocarbon ethers ( CF 3 CF 2 OCF 2 CF 3 , CF 3 OCF 2 OCF 3 , and – CF 2 OCF 2 OCF 2 –) and their hydrocarbon analogs have been used in a model study of the bonding of fluoroether lubricants to the amorphous-carbon (a -CH) overcoats used to protect the surfaces of magnetic storage media. These small ethers allow measurement of desorption kinetics and allow study of the heats of adsorption, a property that cannot be measured directly using the perfluoropolyalkylether lubricants themselves. The a- CH films used in this investigation were provided by three commercial manufacturers of magnetic storage disks. In all cases, the heat of adsorption of the hydrocarbon ether was greater than that of the corresponding fluorocarbon ether, suggesting that the ethers are bonded to the films through donation of the electron pairs on the oxygen atom. The a- CH films are heterogeneous, exposing a variety of adsorption sites at which the ethers bond with a range of interaction strengths. The hydrogen content of the a- CH films was varied by heating, which induced dehydrogenation at temperatures in excess of 500 K. Most interestingly, systematic dehydrogenation of the films results in an increase in the heats of adsorption of all ethers. We propose a model in which the electropositive nature of the hydrogen in the a- CH films weakens the extent of electron donation from the ether lone pairs and, hence, weakens the bonding of the ethers to the a- CH films. The implication of this model is that it should be possible to control the interaction of lubricants with a- C films by varying the types and concentrations of heteroatoms in the films.