47 research outputs found
Effects of Conformational Isomerism on the Desorption Kinetics of N-Alkanes from Graphite
The dynamics of oligomer desorption from surfaces have been studied by measuring the desorption
kinetics of a set of n-alkanes from the surface of single crystalline graphite. Desorption rates were
measured using a set of 21 monodispersed n-alkanes (CNH2N12,
Desorption Kinetics of Polyether Lubricants from Surfaces
Desorption or evaporation is one of the mechanisms for loss of perfluoropolyalkylether (PFPE) lubricants from the surfaces of data
storage media. One approach to minimizing PFPE loss to desorption is the use of lubricants with increasing molecular weight or increasing
average chain length. In order to understand the effects of chain length on the lubricant evaporation kinetics we have studied the desorption
kinetics of monolayer films of oligomeric ethers with varying chain length adsorbed on the surface of graphite. The desorption preexponents,
Ī½, and desorption barriers, ĪEā”des, have been measured for poly(ethylene glycol) dimethyl ethers, CH3O(CH2CH2O)mCH3,
with m = 1, 2, 3, 4, 8 and 10. These are models for the PFPE known as Fomblin Z, which has a structure CF3O(CF2CF2O)x(CF2O)yCF3.
The results show that the desorption pre-exponents are independent of chain length and have an average value of Ī½ = 1018.7Ā±0.3 sā1. The ĪEā”des for the poly(ethylene glycol) dimethyl ethers vary non-linearly with chain length and can be fit with a power law expression of the
form ĪEā”des = a + b Ā· NĪ³ , where N is the total number of atoms in the oligomer backbone (N = 3m + 3) and the scaling exponent has a
value of Ī³ ā 1/2. This non-linear dependence of ĪEā”des on chain length has also been observed in recent studies of the desorption kinetics
of straight chain alkanes from graphite. A desorption mechanism is described that explains the non-linearity of ĪEā”des for the poly(ethylene
glycol) dimethyl ethers. The implication for the lifetime of lubricants on data storage media is that the long chain PFPE lubricants desorb
more rapidly than one might expect based on simple linear scaling of the ĪEā”des of lower molecular weight PFPEs