We present a mean field theory to describe volume phase transitions of side-chain liquid crystalline gels.Three different uniaxial nematic phases(N_1,N_2,and N_3)are defined by using orientational order parameter S_m of side-chain liquid crystals(mesogens)and S_b of backbone chains.We derive the free energy for the three nematic phases of side-chain liquid crystalline gels dissolved in isotropic solvents and calculate the swelling curve of the gel,the order parameters of a backbone chain and of side-chain liquid crystals,and the deformation of the gel as a function of temperature and an electric field.We find isotropic-nematic(N_1,N_2,and N_3)and N_1N_2 phase transitions of the gels,depending on the interaction between a backbone chain and a side-chain liquid crystal.
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