Liquid-Crystal-Elastomer-Actuated Reconfigurable Microscale Kirigami Metastructures.

Mingchao Zhang,Abdon Pena‐Francesch,Metin Sitti,Hamed Shahsavan,Yingying Zhang,Yubing Guo

doi:10.1002/adma.202008605

Abstract

Programmable actuation of metastructures with predesigned geometrical configurations has recently drawn significant attention in many applications, such as smart structures, medical devices, soft robotics, prosthetics, and wearable devices. Despite remarkable progress in this field, achieving wireless miniaturized reconfigurable metastructures remains a challenge due to the difficult nature of the fabrication and actuation processes at the micrometer scale. Herein, micro-scale thermo-responsive reconfigurable metasurfaces using stimuli-responsive liquid crystal elastomers (LCEs) is fabricated as an artificial muscle for reconfiguring the 2D microscale kirigami structures. Such structures are fabricated via two-photon polymerization with sub-micrometer precision. Through rationally designed experiments guided by simulations, the optimal formulation of the LCE artificial muscle is explored and the relationship between shape transformation behaviors and geometrical parameters of the kirigami structures is build. As a proof of concept demonstration, the constructs for temperature-dependent switching and information encryption is applied. Such reconfigurable kirigami metastructures have significant potential for boosting the fundamental small-scale metastructure research and the design and fabrication ofwireless functional devices, wearables, and soft robots at the microscale as well.

Highlights

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The schematics of the synthesis and molecular alignment of the liquid crystal elastomers (LCEs) film followed by the 3D printing of kirigami microstructures are shown in Figure 1C-i–vii. i) In brief, the LCE precursor mixture was injected into capillary cells with a ≈200 μm gap and left at room temperature for at least 5 h to render the Michael addition. ii–iv) the cell was cleaved, and the resulting swollen gel was dried in an oven under the vacuum at 50 °C for at least 6 h
The second step of cross-linking was carried out by exposing the stretched LCE film to ultraviolet light (UV). v) The fully cross-linked monodomain LCE film with a thickness of ≈100 μm was laser-cut into 1.5 mm × 1.5 mm square films that would act as the artificial muscle

Summary

Results and Discussion

Our design of microscale programmable and reconfigurable metasurfaces is schematically shown in Figure 1A, where an overhanging kirigami microstructure is 3D printed via the. Due to the large thermomechanical mismatch between IPS780 and LCE, raising the temperature of the systems with thinner IPS780 layers led to the appearance of surface wrinkling as a result of Euler structural instabilities[50] (highlighted with red dash line in Figure 3B), for samples with h < 5 μm Such local out-of-plane deformation of IPS780 layers led to a significant decrease in the width (S1) of the anchoring posts due to the thermal shrinkage of the LCE film along its director field (Figure 3C). Samples with this optimal thickness resisted the swelling of the LCE film to prevent the pre-stretching, and experienced shape transformation only after they reached their threshold stress in the vicinity of TNI. No discernible pattern was observed for samples with δ/l values comparable to that of backgrounds, even at elevated temperatures (Figure S5b–d, Supporting Information)

Conclusions

Experimental Section

Conflict of Interest

Data Availability Statement