Thermally cured low surface-tension epoxy films

A simple method is described on the preparation of low surface-tension epoxy films via thermal curing. First a partially fluorinated diamine was synthesized by reacting perfluoroalkyl epoxide with a known excess of diamine. Then a mixture of the fluorinated diamine and diglycidyl ether of bisphenol-A was thermally cured, resulting in films with surface tensions as low as 15 mN/m by using less than 2 wt% of perfluoroalkyl epoxide. The fluorinated species segregated preferentially at the film surface to minimize the coating-air interfacial energy. The surface tension of the epoxy films can be adjusted by varying the type of the fluorinated epoxides and their amounts. The surface enrichment of fluorine was verified by angle-resolved X-ray photoelectron spectroscopy (XPS), showing a more than 80-fold excess in the outermost ∼9 nm compared to the theoretical bulk concentration. Deeper depth profiles on the fluorine content were qualitatively revealed by dynamic secondary-ion mass spectrometry (DSIMS) measurements.