End Group Effects on Adhesion of Perfluoropolyether Lubricants to Solid Substrates

Interfacial interactions of several commercial perfluoropolyether (PFPE) and aromaticmodified lubricants with silicon oxide or carbon substrates were investigated through contact angle measurement, dipping tests, fluorescence spectroscopy and contact-start-stop testing. All commercial lubricants that have not been thermally treated are displaced from the solid substrate by contact with water. Contact angles of water on ZDOL, a PFPE doubly-terminated with hydroxyl groups, spun on silicon and carboncoated wafers were measured as a function of thermal annealing treatment. The adhesion of commercial lubricants to such previously thermally-bonded layers is stronger than to the bare silicon wafers. The thermal reaction of ZDOL on silica gel and carbon was investigated by thermogravimetric analysis and FTIR. The thermal reaction takes place when the baking temperature exceeds 70°C; at least part of this surface-bonding involves condensation of terminal hydroxyl groups with isolated surface silanols. Finally, stiction values for aromatic-modified lubricants are substantially lower than for the unmodified commercial PFPE lubricants, but there are still significant humidity effects.