Orientation-on-demand thin films: Curing of liquid crystalline networks in ac electric fields

Electric fields have been used in the processing of thin film, liquid crystal thermosets to produce cured network structures selectively oriented either parallel or perpendicular to a film substrate. Orientation, which depends on both the liquid crystal nature of the thermosets and their dielectric anisotropy, is selected by varying the frequency of the alternating electric field and is locked into a robust network structure by a cross-linking reaction that takes place concurrent with orientation. Structural changes and orientation during the curing reaction were measured in real time with synchrotron x-ray diffraction. Diffraction studies show that, before curing in a modest electric field of 1 volt per micrometer, reorientation can be induced by changing, for example, from a high-frequency (>1000 hertz) to a low-frequency (<50 hertz) electric field, which causes a 90-degree flip in the molecular orientation.