Mechanics of liquid crystals and application to micro-actuators

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When a liquid crystal is filled between two parallel plates and a voltage is applied to the liquid crystal with all molecules initially orienting parallel to the plates, the molecules except for wall vicinity rotate around their center of gravity and reorient to the direction perpendicular to the plates. As a result, a flow is induced between the plates. Application of this phenomenon leads to development of new actuators which have completely different mechanism from that in a past; that is, because a liquid crystal behaves like a liquid, the new actuators have some advantages such as simple mechanism, shape compatibility, easy downsizing, and low-voltage driving.In this study, we have studied the effect of applied voltage, gap of the plates, and twist and tilt angles on the induced velocity, flow rate, and shear stress acting on the plate. When the twist angle is 0 deg, the induced flow is planar, and when the twist angle is not 0 deg, on the other hand, the flow has an out of plane … More component. With increasing the applied voltage, the shear stress acting on the plate, the velocity, and the flow rate are increased and the response is improved. The effect of the gap of the plates is large, while the tilt angle has comparatively little effect.In addition, we have performed an experiment with using a cell device, in which the upper plate is kept movable, while the lower one is fixed. Furthermore, numerical simulation of motion of the upper plate has been done using the Leslie-Ericksen theory as a constitutive equation. Since the rotation of molecules on applying a voltage is opposite to the rotation when we release the voltage, the upper plate repeats forward and backward movements. However, the rotation speed on applying the voltage is larger, so that the upper plate resultantly moves forward. The maximum speed of the plate is 90 μ m/s at the frequency of the applied voltage of 100 Hz. Numerical predictions show the step-like movement, which is qualitatively agreed with the experiments. However, the predictions are larger than the experiments because in simulations we have ignored the friction between the upper plate and particles used for keeping the gap of the plates constant. Less