Active Polymers for Renewable Functional Actuators

Funded by the ERC the APRA project will bridge from the material concept to breakthrough technology: tuning the material design for robust nematic LCE vitrimers, imparting photo-actuation capacity with a controlled wavelength – and finally utilising them in practical-engineering actuator applications where the reversible large-stroke mechanical action is stimulated by light, heat, or solvent exposure.

The idea of mechanical actuator based on intrinsic material properties of liquid-crystalline elastomers (rather than complex engineering of interacting components) has been understood for 20+ years. The remarkable characteristics of liquid-crystalline elastomer (LCE) actuation: fully reversible action; large-amplitude, with a stroke of up to 300%; stress-strain-speed response almost exactly matching the human muscle – make it highly attractive in biomedical engineering, robotics, smart textiles, and many other fields. Yet, there is a profound difficulty (a bottleneck), which remains the reason why this concept has not yet found its way into any practical devices & applications. LCE actuation requires alignment of the local anisotropy (monodomain structure) in the permanently crosslinked polymer network – which has been impossible to achieve in any useful large-scale configuration other than in the flat film, due to the unavoidable restrictions of two competing processes: orientational alignment and network crosslinking.

Recently, we have made a breakthrough, developing LCE vitrimers (polymer networks covalently crosslinked by a bond-exchange reaction: in our first attempt – transesterification). Vitrimers are much more stable than other transient elastomer networks, allow easy thermal re-moulding (making the material fully renewable), and permit moulding of complex shapes with intricate local alignment (which is impossible in traditional elastomers with permanent crosslinking). This ERC project will bridge from the material concept to real technology, developing application demonstrators that include (but not limited to): continuously spinning light-driven motor, tactile dynamic Braille display, capillary pump and toggle flow switch for microfuidics, active textile fibre and shape-changing fabric, and the heliotracking filament that always points at the Sun.

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