Composites containing confined n-octyl-cyanobiphenyl: Monomer and dimer species in the surface layer by in situ FTIR spectroscopy

Confinement of 4-n-octyl-4′-cyanobiphenyl (8CB) to nanoporous molecular sieves with hexagonal structure of cylindrical pores (4.6 nm diameter) is studied. Thermogravimetric investigations have indicated that the pores are completely filled. Several surface species inside the pores and onto the external surface of the grains were demonstrated by differential thermal analysis and by in situ infrared spectroscopy. Arguments are given that bulk-like monomer and dimer species along with hydrogen bonded ones might coexist in the so-called surface layer, but their population varies drastically as function of the temperature. In addition, chemical changes of the confined liquid crystal are quite possible inside these nanopores, at temperatures lower than for the bulk.