Center for Soft and Biological Matter, Indian Institute of Technology Madras, Chennai 600036, India.
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
ACS Appl Mater Interfaces. 2023 Apr 12;15(14):18362-18371. doi: 10.1021/acsami.3c02472. Epub 2023 Mar 28.
Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.
过去十年间，多位研究人员已经证明了液晶聚合物网络（LCN）薄膜的光诱导振荡行为。同样，最近也有报道称 LCN 薄膜在恒定热刺激下会发生振荡，尽管其机制和控制振荡行为的因素尚未得到很好的理解。在这项工作中，我们通过实验和模拟研究了在恒定热刺激下 LCN 薄膜表现出的自维持振荡的动力学。通过扭曲向列相正方形薄膜获得了几何形状不对称的薄膜，例如直角三角形和等边三角形。开发了一个使用有限元方法的多物理计算框架来模拟放置在热板上的 LCN 薄膜的振荡行为。该框架考虑了在振荡过程中热传递和机械变形之间的耦合。小的温度波动（≈1°C）与重力引起的扭矩耦合，被证明可以在特定的板温下驱动振荡行为。我们首次表明，通过在两个相对边缘之间创建厚度逐渐变细，也可以在对称形状（例如正方形薄膜）中实现自维持振荡。所研究的不同几何形状的振荡频率在 0.5 到 2.5 Hz 之间。振荡温度取决于薄膜的平均厚度、尺寸和厚度分布。作为一种可能的应用，我们展示了一种使用薄膜的振荡响应的热驱动光学斩波器。
