Anisotropic networks with stable dipole orientation obtained by photopolymerization in the ferroelectric state

In this study a ferroelectric liquid crystal (FLC) monoacrylate (S)-4-(1-ethoxycarbonyl-1-ethyloxy)phenyl 4'-(11-acryloyloxyundecyloxy)biphenyl- 4-carboxylate was used. Room-temperature spontaneous polarization of the monoacrylate was measured to be 190 nC/cm². The monoacrylate was provided with 10% LC diacrylate. After inducing macroscopic molecular and dipolar orientation in the ferroelectric phase, polymerization within the reactive system was induced photochemically. In this way an anisotropic polymer network with a spontaneous polarization was produced. Within this network the crosslinks were formed by the diacrylate molecules. The anisotropic network was transparent and highly birefringent. The system showed high thermal stability and remained anisotropic even after being heated to elevated temperatures. The presence of dipolar orientation within the anisotropic networks was characterized by piezoelectric measurements. The piezoelectric coefficient within these networks was found to be highly dependent on the direction of the applied strain. The highest value was measured in the direction perpendicular to the molecular orientation and was 29 pC/N.