Hybrid organic–inorganic UV-cured films containing liquid-crystalline units

Abstract

Hybrid organic–inorganic films have been prepared through a dual-cure process, involving photopolymerization (UV-curing) of a methacrylic resin and hydrolysis/condensation of alkoxysilane groups, in the presence of three different liquid crystalline oligomers bearing acrylic reactive groups and synthesized on purpose. These UV-curable mixtures have been coated on glass substrates, exposed to UV radiation in inert (nitrogen) atmosphere, then thermally treated in order to promote the occurrence of the sol–gel reaction and finally peeled off from the substrate. The morphology of the obtained films has been investigated by means of scanning electron microscopy, environmental scanning electron microscopy and atomic force microscopy measurements. Significant silica enrichment on the “gas side” of the films (i.e. the side exposed to the UV-radiation) has been found, as well as the occurrence of the formation of interesting silica conical shapes on the same side with respect to the glass counterpart. Because of the constraints exerted by the inorganic domains on the mobility of the polymer chains, the Tg values of the obtained networks have been found to increase in the presence of the silica phases, which also might have contributed to the occurrence of segregation phenomena of the liquid crystalline phases.