Creating a Highly Clear and Energy Absorbing Liquid Crystal Elastomer by Using a Dual Network Structure

Liquid Crystal Elastomers (LCEs) have found applications in various areas such as soft robotics and protective materials due to their reversible actuation and extraordinary energy dissipation capabilities. These properties stem from a unique molecular structure, which allows for a reversible and adjustable phase transition (from nematic to isotropic) and domain configurations (from polydomain to monodomain) when exposed to external stimuli (such as temperature). Furthermore, the polydomain - nematic molecular structure allows for domains, mesogen re-arrangement under external forces, which makes LCEs move more viscously and dissipate more energy, in addition to the polymer chains relaxing.<br/>However, the inherent polydomain structure of LCEs, composed of a few benzene rings connected by strong pi-pi interactions, causes the emergence of micro-scale polydomains. While this structure enhances the remarkable energy dissipation properties, it also scatters visible light, producing hazy polymer films. LCEs typically exhibit reduced energy dissipation with smaller domain structures, resulting in clearer properties. Transparent display and glass protection films require clear LCEs films, which are challenging to produce. In response, we developed Double Network Liquid Crystal Elastomers (DNLCEs) wherein polyurethane serves as a secondary network to promote the segregation of liquid crystal molecules into minute phases. This makes the domain size very small, reducing light scattering and improving transparency. Significantly, it keeps the domain structure, which preserves the high energy dissipation of polydomain LCEs.<br/>Using Dynamic Mechanical Analysis (DMA) and Small-Angle X-ray Scattering(SAXS), DNLCEs were tested for how well they dissipate energy and their nanoscale molecular structure under large cyclic load, and UV-VIS spectroscopy measured their transparency to visible light. The findings highlight that DNLCEs offer distinct advantages over conventional LCEs, positioning them as promising materials for applications requiring both transparency and superior energy dissipation.