This Faculty Early Career Development (CAREER) grant will pioneer a novel approach towards manufacturing tailored liquid-crystalline elastomers (LCEs), while uncovering fundamental structure-programming-performance relationships within these materials. LCEs are a class of smart and active polymers that can reversibly and repeatedly change their shape in response to a stimulus such as heat. Shape-changing polymers have tremendous potential to produce a variety of actuator applications such as artificial muscles or minimally invasive biomedical devices; however, LCEs have yet to be successfully developed into these applications because of processing limitations. If successful, the proposed two-stage reaction will overcome current chemistry and manufacturing barriers by providing explicit control over polymer structure and domain alignment. This approach will significantly increase the size scale at which LCEs can be produced, while providing a faster and more repeatable reaction mechanism compared to traditional approaches. As a result, this research will uncover the key relationships to enable the design and development of LCEs for a range of applications. An annual summer workshop series is planned to motivate and attract high school students to pursue careers in engineering.
One of the major challenges for LCEs to perform this shape-switching behavior is that the polymeric chains must be aligned to form a liquid-crystalline domain. A two-stage chemical reaction will be developed using functionalized monomers to overcome the chemistry barrier often associated with the synthesis of these materials. The first stage of the reaction will create a lightly crosslinked liquid-crystal polymer. The influence of both initial crosslinks and temperature on maximum achievable stretch will be investigated in order to optimize the amount of chain alignment. The second stage of the reaction will use ultraviolet light to further crosslink the material and keep the polymer chains in their aligned orientation. The influence of photo-crosslinks will be investigated for the effectiveness of retaining the aligned shape. Ultimately, crosslinking and stretching conditions will be linked to shape-switching performance and work capacity of the LCE materials. The proposed approach utilizes two independent reactions allowing for the initial synthesis and programming of the aligned material to occur at two distinct time points, offering the ability for stretching and crosslinking to occur two separate steps. This feature will not only help promote research collaborations but would enable manufacturing flexibility once the process is fully realized.
