Molecular dynamics (MD) simulations were carried out to gain an understanding of the interfacial interactions and the phase separation process in a polymer dispersed liquid crystalline (PDLC) system. The most important components of the PDLC system of interest are: E7 (an eutectic mixture of cyanobiphenyl liquid crystals), a crosslinked polyacrylate, and octanoic acid (OA). The miscibility of the different components was investigated and the anchoring characteristics of 4-n-pentyl-4 0 -cyanobiphenyl (5CB) molecules on the penta-acrylate polymer surface were analyzed. The effects of introducing a surfactant on the miscibility and the anchoring strengths were also studied. Bilayers of polymer and liquid crystal (LC) of different alignments, show that an amorphous 5CB structure on the polymer surface was energetically most favorable, whereas homeotropic alignment had the next higher energy and planar alignment was the least favorable. Calculated solubility parameters indicate that prior to polymerization, the prepolymer and LC are miscible and OA is equally immiscible with both of them. Upon polymerization, the polymer is no longer miscible with the LC; phase separation occurs and OA acts as a surfactant forming a layer between the polymer and the LC. Anchoring energies calculated from the interfacial tensions indicate that the LC and polymer interface is strong. On addition of the surfactant, the anchoring energy at the interface of the LC and the surfactant becomes weaker. This decrease in anchoring strength may be one of the major factors responsible for a reduction in droplet size and also a lowering of critical field for switching, both of which are observed experimentally in volume holograms made of these PDLC materials.
Посилання на статтю:
Anchoring characteristics and interfacial interactions in a polymer dispersed liquid crystal: a molecular dynamics study / S.S. Patnaik, R. Pachter // Polymer. – 1999. – N 40. – P. 6507–6519.