Liquid crystal elastomer actuators and sensors: Glimpses of the past, the present and perhaps the future

Abstract

Liquid crystal elastomers (LCEs) are programmable materials par excellence. I review the history and state of the art of LCE materials and processing development from the perspective of the important remaining step of moving out of the academic research lab and applying LCEs as soft actuators or strain sensors. After a brief introduction for the non-expert of what LCEs are and which their main advantages and limitations are, I discuss the key breakthroughs that LCE research has undergone over its 50-year history. Building on this and drawing from fresh results from on-going research, I consider possible future development trajectories that would help address the outstanding key obstacles to reach mass production at competitive cost. I end with discussing a selected set of application scenarios with good opportunities for LCEs to perform functions that no other material could deliver. Specifically, I focus on responsive buildings incorporating LCE actuator fibres and sheets/ribbons, structural health monitoring with LCE strain sensors monitoring crack growth and propagation or alerting residents of buildings exposed to dangerous levels of deformation, and kinetic and responsive garments incorporating LCE fibre actuators and/or strain sensors.

Reversible Crosslinking of LC-Materials by Gel-Formation

“…These systems will be described here. Now, soft elastic materials with an LC-phase (usually LC-elastomers) possess many properties, which make them very special and fascinating materials [11,[22][23][24][25][26][27][29][30][31]. They stem from the interplay [11] between the liquid crystalline director and the In this picture, to obtain an LC-elastomer the isotropic liquid has to be exchanged with a liquid crystalline material (see Figure 1), in which the mesogens self-organize in liquid crystalline phases at given temperature intervals [22][23][24][25].…”

“…These systems will be described here. Now, soft elastic materials with an LC-phase (usually LC-elastomers) possess many properties, which make them very special and fascinating materials [11,[22][23][24][25][26][27][29][30][31]. They stem from the interplay [11] between the liquid crystalline director and the deformation of the network (change in its shape).…”

“…Refs. for strong coupling [11,22,23,25,27,29,30,32,33]; refs. for weal coupling [34]; cholesterics [37]; chiral smectic C* [36,39].…”

Sticky Multicolor Mechanochromic Labels

“…Dynamic color control enables communication and interaction between living species in a diversity of biological and artificial environments. − This has been the inspiration for the development of mechanochromic materials whose structural color changes in response to mechanical stimuli. − Cholesteric liquid crystal elastomers (CLCEs) are prominent among such materials as the structural colors can be easily programmed. The colors arise from the helical twisting of anisotropic rod-shaped liquid crystal (LC) molecules along an axis perpendicular to the molecular director which in turn can be tuned by the concentration of the chiral dopant. − The programmable dynamic structural colors of CLCEs make them prominent candidates for information delivery. − However, the mechanochromic effect is usually manifested by translucent thin films, − thus integration with real-world applications is challenging. Moreover, mechanochromic materials are normally limited to uniform color-shifting which restrains their communication capabilities. − Visual information for ornamentation or functional purposes can be conveyed with sticky labels.…”

Modelling and simulation of the cholesteric Landau-de Gennes model

“…This paper presents a numerical method and analysis for simulating cholesteric LCs in order to predict their structural features. Numerical modelling can yield greater insight into the functional effects of cholesteric LCs in biological systems and enable the design of programmable materials [18][19][20].…”