Modeling Mechanical Actuation in Liquid Crystal Polymers
Liquid crystal polymer networks undergo reversible shape change in response to any stimulus that affects their nematic order, allowing them to flex like artificial muscles. These soft actuators can be fabricated as thin films, surface coatings, or 4D printed solids and have potential applications in soft robotics, biomedical devices, microfluidics, and sensors. Trajectories for shape change are “programmed” by patterning the nematic director when the polymer is cross-linked. Actuation is induced when the strength of nematic order is modulated by stimuli such as a change of temperature, chemical environment, or illumination. To model mechanical actuation at the device scale, we use nonlinear finite element method (FEM) elastodynamics simulation based on a Hamiltonian formulation. We examine the mechanism of oscillatory mechanical wave motion driven by self-shadowing in liquid crystal polymer films that drives a light-powered robotic device , and model a variety of other prototype devices including surface-adhered nematic polymer coatings that transform from flat to complex surface profiles with microchannels, spikes, or dimples. Next we model polymer coatings patterned with biomimetic “octopus-like” suckers, designed to grasp and release nonporous objects on command. We compare our modeling results with relevant experiments by our collaborators and discuss potential applications.
 Gelebart, A.H., Mulder, D.J.,Varga, M., Konya, A., Vantomme, G., Meijer, E.W., Selinger, R.L.B., Broer, D.J., Making waves in a photoactive polymer film, Nature 546, 632 (2017) https://doi.org/10.1038/nature22987
Work supported by NSF CMMI-1663041, NSF DMR-1409658, and NSF-CMMI 1436565.