Structure and properties of anisotropic gels and plasticized networks containing molecules with a smectic-Aphase

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Abstract
Liquid-crystal (LC) mixtures of a low-molar-mass LC diacrylate and 4-cyano-4’-octylbiphenyl (8CB) showing a smectic-A phase in the bulk were produced. The mixtures were aligned macroscopically and the polymerization was induced photochemically. In this way, anisotropic networks containing molecules which are not chemically attached to the network (anisotropic gels and plasticized networks) were produced. Using IR dichroism, it was found that, above the nematic-to-isotropic transition temperature of 8CB, a fraction of the molecules remained oriented. This behavior was associated with the presence of two populations of 8CB molecules within anisotropic gels and plasticized networks. One of the populations showed the same behavior as in the bulk (unbound fraction), while the other population was found to be influenced to a large extent by the network (bound fraction) and did not show a first-order nematic-to-isotropic transition. The behavior as observed by IR dichroism was simulated using a theoretical model and the fractions of the bound and unbound 8CB were estimated in systems containing various amounts of networks.