Advances in Liquid Crystal Elastomers

Self-sustainable autonomous soft actuators have emerged as naturally evolving out-of-equilibrium systems that do not require human intervention. Here, the authors discuss recent advances in the field, with a focus on shape-morphing materials, motion characteristics, built-in negative feedback loops, and constant stimulus response patterns.

Liquid crystal elastomers are shape-morphing materials that demonstrate reversible actuation when exposed to external stimuli, and their actuation depends heavily on the liquid crystal alignment programmed into these materials, using various shape-programming processes. Here, the author reviews current shape-programming methods in relation to the challenges of employing liquid crystal elastomers as soft, shape-memory components in devices in the future.

Isotropization temperature determines the temperature at which Liquid Crystals Elastomer (LCE) material actuates. Here, the authors give a general strategy based on dynamic covalent bonds for tuning the isotropization temperature for LCEs.

Soft-elasticity in monodomain liquid crystal elastomers (LCEs) is promising for impact-absorbing applications but due to the lack of synthetic procedures which give monodomain devices of sufficient size, impact studies on LCEs have not been performed. Here the authors use direct-ink writing to fabricate bulk monodomain LCE devices and study their compressive soft-elasticity.

Liquid crystal elastomer printing methods are often limited to planar structures. In this work, authors integrate 4D printed structures with fully impregnated composite interfaces to enable programmable deformation ability and high bearing capacity by adjusting the off-centre distribution of the fibres.

Multifunctional composites have potential in a number of applications, and it is desirable to have control by external stimuli. Here, the authors report a 4D printing method for liquid crystal elastomer composites with continuous fibres capable of multifunctional actuation.

Light diffusion effects in liquid crystals are important for security and lighting devices. Here, viewing angle dependent pearlescence and iridescence are reported in a nematic liquid crystal elastomer with a stabilized director buckling pattern, which can be controlled by deformation or temperature.

Cholesteric liquid crystal elastomers (CLCEs) have tunable optical properties under an external field, but these properties revert once the field is removed. By introducing diselenide dynamic covalent bonds, the authors enable CLCEs to retain tunable optical properties after force and light exposure, achieving programmable, high resolution color patterning.

To date, only one polymer can self grow to an extended length beyond its original size at room temperature without external stimuli or energy input paving the way for significant advancements in untethered autonomous soft robotics but only freshly prepared samples in an initial state can self-grow. Here, the authors propose a strategy to rejuvenate non-fresh samples to their initial state for on demand self-growth through the synergistic effects of solvents and dynamic covalent bonds during swelling.

Untethered soft robots offer numerous advantages in terms of mobility, versatility, and autonomy, making them increasingly valuable for a wide range of applications. Jung et al. review the new types of untethered soft actuators that represent breakthroughs and discuss the future perspective of soft actuators.