ReaxFF Reactive Molecular Dynamics Simulations of Mechano-Chemical Decomposition of Perfluoropolyether Lubricants in Heat-Assisted Magnetic Recording

XY Chen and K Kawai and HD Zhang and K Fukuzawa and N Koga and S Itoh and N Azuma, JOURNAL OF PHYSICAL CHEMISTRY C, 124, 22496-22505 (2020).

DOI: 10.1021/acs.jpcc.0c06486

A thorough understanding of the decomposition of perfluoropolyether (PFPE) lubricants is crucial to achieve heat-assisted magnetic recording (HAMR). In contrast to previous studies, which focused on thermal and catalytic decompositions, we gain insights into the mechanochemical decomposition of PFPE films confined between the head and disk by performing reactive molecular dynamics simulations with our new ReaxFF force field. By quantifying the decomposition time constants under the operation conditions of HAMR, we infer that, within a heating time of similar to 1 ns, pure thermal decomposition hardly occurs, whereas mechano-chemical decomposition is highly likely to occur. The decomposition rate constant of the PFPE films subjected to confined shear increases with normal pressure. The increase is well-fitted by a linear stress-activated Arrhenius curve at high normal pressures, whereas this is not the case at low normal pressures. We caution against extrapolating the linear stress-activated Arrhenius curve, which could cause significant overestimation of decomposition rate constants at low normal pressures. We find that the mechano-chemical decomposition of PFPEs is mainly attributed to the dissociation of C-OH and ether C-O bonds in the polar end groups, and in the main chain, the C-O bond is more likely to dissociate than the C-C bond.

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