Electrorheological response of the interfacial layer between a liquid crystal and a polymer alignment sublayer

The interfacial layer between a liquid crystal (LC) and a polymer alignment sublayer was investigated using the quartz crystal microbalance (QCM) method. The time variations in the optical transmittance through the LC cells and the interfacial viscoelasticity were monitored simultaneously using the QCM to provide a comprehensive picture of the interfacial phenomena associated with the motion of LC molecules both in the bulk and in the interfacial layer. The response time of shift in the resonant resistance associated with the director orientation in the interfacial layer was about 90 ms, while that in the LC bulk was about 5 ms. This indicates that the reorientation of the LC molecules in the vicinity of the interface is much slower than in the bulk. The response time for the changes in thickness of the adsorbed layer, as estimated from the QCM results, was found to be about 1000 ms. These results indicate that the electrorheological response, or the viscoelasticity, in the vicinity of the interface between the LC and the polymer should be taken into account for the development of LC devices.