Perfluorocyclobutyl Polymer Thin Film Plasticization by CO2

In this presentation, we will describe work to understand the plasticizing effect of carbon dioxide on Tetramer Technologies’ perfluorocyclobutyl polymers used for gas separation membranes. Plasticization causes membrane permeance to increase but separation selectivity to decrease. This phenomenon is more significant in thin (<200 nm) polymer films. For this reason, we seek to understand the CO₂plasticization behavior of PFCB polymer thin films. Results of this work will be used by Tetramer Technologies to develop strategies that suppress plasticization and yield membranes with better performance.

In prior work, we described how coating conditions affect PFCB thin film formation using a dip coating method. We used this method to coat composite membranes and silicon wafers with PFCB thin films having controlled, uniform thickness. TEM, ellipsometry and AFM characterization show that films on different substrates have identical thickness and morphologies. Permeance values of CO₂ through PFCB composite membranes were measured over a CO₂ pressure range of 100 psi to 600 psi. In a parallel study, the time-dependent thickness of PFCB thin films on silicon wafers were measured under CO₂ pressure from 100 psi to 600 psi using a specially designed, home-built, high-pressure ellipsometry cell. CO₂ sorption, PFCB density, and glass transition pressure provided further information to understand CO₂ plasticization of PFCB.