The influence of external electric field on local orientations and phase transitions in polymer liquid crystals (PLCs)

The starting point is our previous study of influence of the internal molec ular mean field of dipole-dipole interactions on local orientation and phas e transitions in polymer liquid crystal (PLC) systems of longitudinal chain s.([1,2]) Electric dipoles are created by LC mesogen moieties. The longitud inal PLC is a macromolecule of consecutively copolymerized LC and flexible polymer sequences. We now amplify the model by inclusion of dipole-external electric field interactions. We find that the external fields can seriousl y modify the local orientational order of the system and affect phase trans ition parameters dependent on that order. In particular, the external field s induce the formation of disoriented nematic phases with negative values o f the second order orientation parameter (P-2) for LC sequences in the long itudinal PLCs while the first order parameter (P-1) is positive. However, s ome rapid decreases in (Pi) are observed at points of positive-to-negative transitions of (P2); thus the LC disorientation manifests itself. The limit ing case of the monomer liquid crystal (MLC) systems is included also.