Volatility of perfluoropolyether lubricants measured by thermogravimetric analysis

Abstract

The evaporation rate at ambient pressure as a function of molecular weight has been measured for two functionalized perfluoropolyether lubricants, Zdol and Zdol-TX, using thermogravimetric analysis (TGA). The temperature dependence of the evaporation rate is well characterized by a zero-order Arrhenius expression, allowing determination of the molecular weight dependence of the pre-exponentials and activation energies. These Arrhenius parameters can then be used to extrapolate the evaporation rate back to temperatures where it is too small to be directly measured. The extrapolated evaporation rates at 200°C are combined with Raoult's law to predict the vapor phase molecular weight distribution of Zdol over a polydisperse liquid phase, which is shown to be in reasonable agreement with the measured vapor phase distribution. The evaporation rate of Fomblin Z fluids is also shown to be strongly dependent on the functional endgroup for a given molecular weight. © J.C. Baltzer AG, Science Publishers.