Samuel J. Falcone

Volatility of perfluoropolyether lubricants measured by thermogravimetric analysis

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 Raoults 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.

The ideality of polydisperse perfluoropolyether lubricants with application to physical vapor deposition

We have used thermogravimetric analysis (TGA) to measure the evaporation rate as a function of temperature and molecular weight for an alcohol-derivatized perfluoropolyether (PFPE), Fomblin Zdol. We show that the bulk evaporation rate of a polydisperse Zdol solution during temperature ramp TGA can be numerically simulated by combining molecular weight dependent Arrhenius parameters, the initial molecular weight distribution as measured by size exclusion chromatography, and Raoult’s law of vapor pressures. The simulation is shown to be in good agreement with experiment for both a low molecular weight polydisperse Zdol, and for a mixture of the low molecular weight Zdol with a heavier Zdol fraction. Mixtures of Zdol with non-functionalized Z lubricants are shown qualitatively to deviate substantially from ideality. In the disc drive industry, physical vapor deposition (PVD) is receiving renewed interest as an alternative method of applying the PFPE lubricants commonly employed as topical coatings on thin film magnetic media. In a process involving vaporization of a polydisperse liquid phase lubricant, quantitative prediction of deposition rates and vapor phase molecular weight distributions will in general only be possible with accurate knowledge of liquid phase distributions, component evaporation rates, and the ideality of the solution.