Subcritical Phase Transitions in Supramolecular Liquid Crystalline Elastomers

Liquid crystalline elastomers (LCEs) are commonly used as soft actuators for applications such as robotics but are currently limited by a weak coupling of stimuli and response that restricts these materials for functional applications. This is evident in the extended deformation-temperature response of LCEs that is an inefficient use of energy. Fundamentally, LCEs exhibit continuous (2^nd order) phase transitions between nematic and isotropic (paranematic). Motivated by this fundamental limitation of these materials, this effort attempts to approach quasi-1^st order (subcritical) phase transitions in LCEs. Here, we introduce supramolecular hydrogen bonds in the mesogens of the polymer network that dissociate upon heating. The efficiency of phase transitions in LCEs is currently limited by the retention of order in the paranematic phase due to the retainment of crosslinks. By introducing non-covalent bonds using benzoic acid precursors as dimers within crosslinks, the polymer network can be disrupted more rapidly than seen in prior reports. Here, we also introduce liquid crystalline mesogens with weaker intermolecular interactions to combine lower, more accessible transition temperatures with sharper transitions. Overall, the purpose of this effort is to lead to improved performance of these functional materials as rapid soft actuators for robotics applications.