Observation of memory effects in 5CB/PVAc liquid crystal-polymer composites

A study of the memory effect in polymer-dispersed liquid crystal composites based on 4-cyano-4'-pentylbiphenyl (5CB) and polyvinyl acetate (PVAc) obtained by solvent-induced phase separation is presented. Using an original high-precision bridge circuit, it is demonstrated that a cyclic voltage application causes conditionally irreversible capacitance changes exclusively in 5CB/PVAc = 2/1 composites, with the memory parameter M = 0.17 after the first polarization cycle. The effect shows a limited accumulation (M increases only to 0.19 in subsequent cycles) and can be completely eliminated by heating above the temperature of the nematic-isotropic transition. Polarization microscopy revealed key morphological differences: the liquid crystal is displaced into homogeneous spherical droplets (50–70 μm) in the 5CB/PVAc = 1/1 composites, while the 2/1 systems exhibit complex phase delamination with characteristic 'four-leaf clover' defects (50–200 μm) containing disclinations with a winding number of +1. This morphology indicates the tangential orientation of 5CB at the polymer interfaces. The short-term thermal effect destroys these clover structures, thus forming 10 μm domains and eliminating the director field configuration required for memory retention. The memory effect originates from metastable director configurations in non-spherical cavities, where surface anchoring enables degenerate axes aligned with the applied field. The demonstrated effects enable novel functional devices based on electrically programmable LC-polymer memory systems.