A comparative study of the kinetics and energetics of oligomer desorption from graphite

Abstract

The desorption kinetics of polyethyleneglycols (PEGs) of varying chain length, N, have been studied on the surface of graphite. The chain length dependence of the Δ E des ‡ has been measured for PEGs and compared with those of n-alkanes and polyethyleneglycol dimethylethers (PEG-DMEs) adsorbed on graphite. The short PEGs have higher Δ E des ‡ than PEG-DMEs of comparable length. More importantly, in the short chain regime ( N < 30) the Δ E des ‡ of the PEGs are linear in chain length while the Δ E des ‡ of the n-alkanes and PEG-DMEs are non-linear in chain length. For long chain lengths ( N > 30) the Δ E des ‡ of the PEGs become non-linear and approach those of the PEG-DMEs. The differences between the short chain PEGs and the n-alkanes and PEG-DMEs are attributable to the hydroxyl endgroups of the PEGs.