Fluid Structural Interactions of Flapping Photomechanical Liquid Crystal Polymer Networks

A class of active polymers that respond mechanically to ultraviolet and visible light is studied using an advanced fluid-structural interaction model that photomechanically couples three dimensional, unsteady Navier-Stokes equations with a plate model of liquid crystal networks. These materials have been shown to exhibit fast response times that scale with the resonant frequency of the polymer film structure. Moreover, these films are classified as glassy (modulus ∼ 1GPa) and thus have demonstrated flapping behavior on the order of 100Hz or greater in millimeter length films. A variety of applications include micro-propulsion systems for insect size aircraft and biomedical actuators for micro-manipulation of biological materials. A critical challenge in utilizing these materials is explored here by quantifying photomechanical performance and efficiency under unsteady, aerodynamic loads. To quantify the active material performance, we utilize detailed fluid-structural computational methods that couple light input energy, strain energy of the photomechanical film, and interactions with ambient air. The effect of ambient air pressure is found to have a significant impact on photomechanical performance.