Dynamic behavior of hybrid organic-inorganic composites:: liquid crystals confined in SBA-15 mesoporous materials

Molecular dynamics of a nematic liquid crystal, 4n-octylcyanobiphenyl, confined to two types of SBA-type nanoporous molecular sieves were studied by broadband dielectric spectroscopy in order to obtain information about the liquid crystal-surface interactions. The temperature interval of the dielectric measurements was large, covering all the states of the bulk liquid crystal. It is found that there are several relaxation processes covering the large frequency range. A bulk-like relaxation comes from the liquid crystal molecules located in the center of the pores, which rather do not feel the effect of the pore walls. Another relaxation comes from the molecules located in the surface layer. The latter process is much slower than the bulk-like relaxation. The differences observed between the dynamic behavior of the liquid crystal confined to the two types of nanoporous materials are related to pore size, pore shape and liquid crystal-surface interactions.