Anisotropic swelling and phase behavior of monodomain nematic networks in nematogenic solvents

Equilibrium swelling behavior of uniaxially oriented nematic networks in nematogenic solvents has been studied in the temperature (T) range covering the two independent nematic-isotropic transition temperatures for the swollen network (T-NI(G)) and the surrounding solvent (T-NI(S); T-NI(G) > T-NI(S)). The swollen isotropic state smoothly changes into the shrunken nematic state with an elongation along the director axis within a narrow temperature range around TNIG. In the region of T-NI(S) < T < T-NI(G), where the surrounding solvents are in the isotropic state, the shrunken nematic gels reswell with a further increase in shape anisotropy upon cooling. In the totally nematic phase of T < T-NI(S), the shape anisotropy increases without significant volume change with decreasing T. A mean field theory satisfactorily describes the features of experimental data, although a sharp transition predicted disagrees with the smooth transition observed. The polydomain nematic network without global director orientation shows no anisotropy in swelling but exhibits substantially the same T dependence of swelling degree as the corresponding monodomain system. A striking difference is that the polydomain system undergoes a discontinuous volume transition, unlike the continuous transition in the monodomain system.