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

The desorption kinetics of polyethyleneglycols (PEGs) of varying chain length, N, have been studied on the surface of graphite. The chain ength dependence of the 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 E des than PEG-DMEs of comparable length. More importantly, in the short ‡ ‡ hain regime (N< 30) the Edes of the PEGs are linear in chain length while the Edes of the n-alkanes and PEG-DMEs are non-linear in hain length. For long chain lengths (N> 30) the E des of the PEGs become non-linear and approach those of the PEG-DMEs. The differences etween the short chain PEGs and the n-alkanes and PEG-DMEs are attributable to the hydroxyl endgroups of the PEGs. 2004 Elsevier B.V. All rights reserved.