Simulation-based Design of Temperature-responsive Nematic Elastomers
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Liquid crystal elastomers (LCEs) are a class of polymer networks which involve the incorporation of liquid crystal (LC) molecules into their polymer backbone or side chain. This results in anisotropy in their mechanical, optical, and electromagnetic properties similar to those exhibited by traditional LC materials. Their mechanical properties are highly coupled to the internal state of LC order, which can result in large mechanical deformations as LC order changes. This can occur in response to a variety of external stimuli such as changes in temperature, exposure to light, and application of external fields. The interplay between LC order and mechanical properties makes LCEs a highly promising class of functional materials and subsequently, they have been the subject of much research over the past several decades. However, developing an application of LCEs remains difficult in that their mechanical response is both complex and coupled to the state of liquid crystal order prior to cross-linking. Their physics are sufficiently complicated that in most cases, the use of pen-and-paper analysis is precluded. Additionally, the LCE fabrication process is complex and expensive, making trial-and-error experimental design methods unsuitable. This motivates the development and use of simulation-based methods to augment traditional experimental design methods. The two main contributors to the complexity of the design of LCE applications are the choice and imposition of liquid crystal order, or "texture", prior to cross-linking. In this work, simulation-based methods are developed and partially validated for use in applications-focused design of temperature-responsive nematic LCEs. These methods enable the simulation of LCEs of macroscopic size and of non-trivial geometry through the use of continuum mechanics and suitable numerical methods (the finite element method). LC texture is an input parameter in the presented method, allowing many choices of texture to be explored at low cost given that the textures are physically accessible. In addition to methods development and validation results, proof-of-concept simulation-based design studies were performed for two types of LCE-based actuators that are of current interest in the field: grippers and hinge mechanisms. Finally, preliminary results are presented resulting from the integration of nematic texture dynamics simulation (pre-cross-linking) and LCE mechanical simulations (post-cross-linking) which address the two main sources of complexity in the design process of LCE functional materials.
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Ryan Alexander Epp Neufeld (2017). Simulation-based Design of Temperature-responsive Nematic Elastomers. UWSpace. http://hdl.handle.net/10012/12022