THE THERMAL-STABILITY OF PERFLUOROPOLYETHERS ON CARBON SURFACES

The thermal decomposition of several perfluoropolyethers (Demnum S65, Demnum SP, and Fomblin ZDOL) is studied by thermal programmed desorption on both graphite and amorphous carbon surfaces. Molecules having a CF2-CF3 endgroup (Demnum S65) showed enhanced thermal stability with respect to a CF2-CF2-CO2-CH2-CH2O-phenyl endgroup (Demnum SP). On graphite, Demnum SP showed a low temperature desorption feature at 580 K, as well as features at 650 and 800 K, while Demnum S65 only showed features at 660 and 800 K. At approximately 600 K the reactive endgroup from the Demnum SP molecule is lost, together with fluorocarbon compounds, while the 800 K feature corresponds to oxygen containing fluorocarbon compounds. This high temperature feature at 800 K is not observed during the decomposition of the perfluoropolyethers on amorphous carbon substrates, indicating that this surface has a more reactive nature compared with graphite. For Fomblin ZDOL on graphite, the two main desorption features are at 620 and 770 K, slightly lower in temperature than the similar features observed for Demnum S65. On amorphous carbon, the main desorption features observed for Fomblin ZDOL are at 510 and 650 K. The results show the importance of the substrate and the endgroup of the perfluoropolyether molecule in the thermal stability of thin perfluoropolyether films on surfaces.