INFLUENCE OF THE PHASE-SEPARATION MECHANISM ON POLYMER-DISPERSED LIQUID-CRYSTALLINE MATERIALS

We have studied the phase separation mechanism accompanying the format ion of polymer dispersed liquid crystals (PDLC). Different polymers an d liquid crystals were used, including epoxy resins, fluorinated macro molecules, eutectic mixtures and single component mesophases. Various phase separation methods, such as solvent evaporation and polymerizati on of the components, have also been employed. Results show that PDLC' s can be obtained by nucleation and growth and by spinodal decompositi on of an initially homogeneous mixture. In samples formed via this las t mechanism, the characteristic length of the fastest growing concentr ation modulation in the first stage of the decomposition is still evid ent, in the morphology of the cured samples, as an alignment of the dr oplets in rows. Other physical properties of the material are unaffect ed by the decomposition mechanism, except in the case of concentration s close to the spinodal line. Such last samples exhibit dramatically d ifferent electrical resistivity and also different x-ray patterns and IR spectra. Such differences are probably correlated with a particular packing of the polymer chains induced by the peculiar conditions of p hase separation for samples near the spinodal line. Implications of th ese properties for PDLC technological applications are discussed.