Thermal bending coupled with volume change in liquid crystal gels

Quantitative analysis of bending hysteresis by real-time monitoring of curvature in flexible polymeric films

Flexibility, viscoelasticity and stress-strain relation in bending polymeric films are key factors in designing mechanically durable flexible electronic devices and soft robots. However, bending hysteresis, which appears as a precursor phenomenon of fracture and fatigue, remains unclear; no one quantitatively evaluated a bending curvature causing hysteresis. Herein, we report the bending hysteresis of polymeric films used as common substrates in flexible electronics by precisely monitoring bending curvatures. By real-time measuring curvatures of films upon bending and subsequent unbending, we have successfully determined the curvatures that cause the hysteresis. These curvatures also depend on a film thickness. Furthermore, we revealed that the occurrence of bending hysteresis is explained by bending strains that have a nonlinear relation with internal stresses. This enables us to predict strain limits that cause the bending hysteresis, based on a stress-strain curve of polymeric films.

Bioinspired underwater locomotion of light-driven liquid crystal gels

Soft-bodied aquatic invertebrates, such as sea slugs and snails, are capable of diverse locomotion modes under water. Recapitulation of such multimodal aquatic locomotion in small-scale soft robots is challenging, due to difficulties in precise spatiotemporal control of deformations and inefficient underwater actuation of existing stimuli-responsive materials. Solving this challenge and devising efficient untethered manipulation of soft stimuli-responsive materials in the aquatic environment would significantly broaden their application potential in biomedical devices. We mimic locomotion modes common to sea invertebrates using monolithic liquid crystal gels (LCGs) with inherent light responsiveness and molecular anisotropy. We elicit diverse underwater locomotion modes, such as crawling, walking, jumping, and swimming, by local deformations induced by selective spatiotemporal light illumination. Our results underpin the pivotal role of the physicomechanical properties of LCGs in the realization of diverse modes of light-driven robotic underwater locomotion. We envisage that our results will introduce a toolbox for designing efficient untethered soft robots for fluidic environments.

Exploration of immobilization conditions of cellulosic lyotropic liquid crystals in monomeric solvents by in situ polymerization and achievement of dual mechanochromism at room temperature

We investigated conditions to prepare cellulosic cholesteric liquid crystalline (ChLC) films in order to accomplish dual mechanochromism, i.e., colour control and circular dichroic inversion upon mechanical stimulus, at room temperature. Flexible propionylated hydroxypropyl cellulose (PHPC) was prepared by a simple reaction and found to be capable of forming lyotropic ChLC in various monomeric solvents. The ChLC solutions were subjected to in situ polymerization to obtain PHPC/synthetic polymer composite films incorporating the ChLC structure. However, the immobilization behaviour depended on the type of original monomers. Differential scanning calorimetry and solid-state NMR measurement revealed that the ChLC structure was more highly fixed when the compatibility between PHPC and the coexisting polymers was lower. Eventually, thus obtained ChLC composite films exhibited dual mechanochromism under ambient temperature.

Liquid crystal polymers with motile surfaces

In analogy with developments in soft robotics it is anticipated that soft robotic functions at surfaces of objects may have a large impact on human life with respect to comfort, health, medical care and energy. In this review, we demonstrate the possibilities and versatilities of liquid crystal networks and elastomers being explored for soft robotics, with an emphasis on motile surface properties, such as topographical dynamics. Typically the surfaces reversibly transfer from a flat state to a pre-designed corrugated state under various stimuli. But also reversible conversion between different corrugated states is feasible. Generally, the driving triggers are heat, light, electricity or contact with pH changing media. Also, the macroscopic effects of those dynamic topographies, such as altering the friction, wettability and/or performing work are illustrated. The review concludes with the existing challenges as well as outlook opportunities.