ANISOTROPY OF NONMESOGENIC POLYMER NETWORKS DISPERSED IN A LIQUID-CRYSTAL MATRIX

We report here original results characterizing in situ the interaction s between a smectic liquid crystal phase and a polymer network dispers ed in it. These results have been obtained by neutron scattering on sm ectic liquid crystal (8CB) samples containing a physical network of 1. 5 wt% polymer. The samples were polymerized in the isotropic, or in th e smectic A phases. For the first time it is experimentally proved tha t the polymerization of non-mesogenic monomers in an aligned smectic A matrix induces anisotropy in the resulting network. The network becom es elongated along the liquid crystal director. When the polymerizatio n is carried out in the isotropic phase the polymer network has an iso tropic distribution even if a magnetic field, which orients the liquid crystal director, is later applied. On the other hand, studies show t hat after several thermal cycles, the liquid crystal orientational ord er still remained. Without other external constraints, the polymer net work freezes the alignment of the liquid crystal. It is probably impos ed by pendant reticulates on the diffuse liquid crystal-polymer interf aces.