Molecular Engineering of Liquid Crystalline Elastomers Containing Supramolecular Mesogens

Liquid crystalline elastomers (LCEs) are lightly crosslinked polymer networks that exhibit large deformations due to the disruption of liquid crystalline order when exposed to a stimulus. However, LCEs currently demonstrate a weak coupling of stimuli and response that limits the functional application of these materials. A recent effort by our group demonstrated that the inclusion of liquid crystalline mesogens formed with supramolecular bonds results in more rapid phase transitions due to the disruption of the hydrogen bonds. Here, we further analyze the effect of intra-mesogenic supramolecular bonds on the actuation of LCEs to better understand how these contribute to the overall order-disorder response. Benzoic acids are shown to form dimers within the crosslinks that can be disrupted with temperature as well as with the nematic to isotropic phase transition of the overall network. By including these dimers with conventional three ringed liquid crystals as well as nonconventional two ringed mesogens with reduced intermolecular interactions, we probe how the disruption of H-bonds is affected by the surrounding network and heat. We also examine the structure-property effect by varying the supramolecular mesogen itself to analyze the connection between H-bond strength and actuation dynamics. This is demonstrated by including benzoic acid derivatives along with molecules containing functional groups such as pyridines to result in single H-bonds. Varying the strength of hydrogen bonds and mesogenic intermolecular interactions results in improved performance of the LCEs. Overall, this effort’s purpose is to both understand the influence of H-bond interactions on LCEs and then tailor the response of these soft actuators through molecular engineering to improve LCEs as functional materials.