ORIENTATIONS AND PHASE-TRANSITIONS IN UNCROSSLINKED AND CROSS-LINKED POLYMER LIQUID-CRYSTALS

A system of linear polymer liquid crystal (PLC) macromolecules is cons idered. Each macromolecule constitutes an alternating copolymer of fle xible and LC sequences. The macromolecules can be either unconnected o r else connected into a PLC network. The system is characterized with respect to local orientation. Competition between energetic effects of anisotropic orienting interactions between LC sequences and entropic effects determined mainly by flexible parts is considered. The Maier a nd Saupe mean-field approach is assumed for the representation of LC i nteractions. Types and orders of phase transitions that the system can undergo with respect to local order are discussed in terms of the Lan dau classification. All transitions are found to be of the first order . Thermodynamical and structural parameters of the system at phase tra nsition points are represented by phase diagrams. (C) 1998 American In stitute of Physics. [S0021-9606(98)50215-2].