PIEZOELECTRIC NETWORKS OBTAINED BY PHOTOPOLYMERIZATION OF LIQUID-CRYSTAL MOLECULES

A liquid crystal (LC) mixture containing reactive and nonreactive chiral molecules was made. The mixture showed the ferroelectric chiral smectic C phase with a spontaneous polarization of 10 nC cm-2 at 80-degrees-C. Upon photoinduced photopolymerization of the reactive molecules in the ferroelectric phase, a highly transparent oriented network with a dipolar orientation was produced. When such a film was subjected to periodic oscillations, a periodically varying open-circuit voltage across the sample could be detected,showing the piezoelectricity of the material Using X-ray diffraction the origin of the piezoelectricity was related to the presence of chevrons and the tilted orientation of the molecules. The sign and the magnitude of the piezoelectric constant were largely dependent on the direction of the applied strain, and in the direction parallel to the molecular orientation it was found to be 3.1 pC N-1.