Programmable and Reversible 3D-to-3D Shape Transformation: Hierarchical Multimodal Morphing Based on Liquid Crystal Elastomers

Abstract

Achieving programmable morphing in 3D-to-3D shapes of soft actuators based on liquid crystal elastomer (LCE), particularly those with multimodal transformations and non-zero Gaussian curvature, remains a significant challenge. Here, a facile strategy is presented to create 3D LCE-elastomer (LCE-Ela) bilayer structures capable of customizable and programmable 3D-to-3D shape transformations, generating reversible and multimodal morphologies with nonzero Gaussian curvature. By combining two types of mismatch strains-pre-stretch and thermal strains-in LCE-Ela bilayer, the approach enables hierarchical multimodal transformations: starting from a 2D initial configuration, programmable transformations enable the formation of complex 3D structures, which can subsequently transition into other 3D shapes following predefined programs, with each step of the hierarchical process allowing multimodal deformations to generate diverse structural morphologies. Experimental and computational demonstrations include over 30 diverse 3D LCE-Ela configurations, the majority of which exhibit nonzero Gaussian curvature. Moreover, biomimetic LCE-Ela structures-including a chameleon, butterfly, spider, and leaf-demonstrate vivid deformation and discoloration, showcasing their potential for applications such as information encryption, camouflage, and adaptive devices. This work provides a facile approach to generate customizable 3D-to-3D transformations with complex geometries, broadening the application scope of LCE-based technologies in 3D soft actuators.

Keywords: 3D‐to‐3D shape morphing; LCE‐Ela bilayer; hierarchical multimodal transformations; mismatch strain driven; programmable and reversible.

Figure 1

Schematic illustration of the mechanism and programming of hierarchical multimodal morphing. a) The two hierarchical transformations are achieved by pre‐stretched strain from the LCE‐Ela bilayer and thermal strain in LCE, respectively. The pre‐stress within the LCE layer is released, causing the bilayer film to deform into 3D structures, and then, through thermal actuation, this 3D structure undergoes further transformation into other 3D configurations driven by the anisotropic thermal deformation of the LCE material. b) The patterned mismatch strain and the application of pre‐strain and thermal strain in specific orientations are carried out to achieve the programmable desired 3D LCE‐Ela structures and multimodal 3D shape morphing i). Furthermore, this strategy easily creates vivid 3D LCE‐Ela structures with 3D shape transformations and color changes through coating thermochromic ink, used for biomimetic camouflage ii) and information encryption iii).

Figure 2

3D LCE‐Ela structures with 3D‐to‐3D hierarchical shape morphing strategy via mismatch strain induced by stress relaxation, and the mechanical and thermodynamic properties of the LCE films. a) Schematic illustration of the fabrication procedure of a representative 2D LCE‐Ela precursor and the reversible 3D‐3D shape‐morphing behavior of the 3D LCE‐Ela structures assembled from it: i) The pre‐stretched LCE films were fixed onto a glass slide. ii) Photosensitive resin was injected onto the films, and another glass slide was placed on top to form a reaction cell. iii) A pattern was projected onto the resin using DLP printing, curing a layer of Ela onto the LCE films. iv) The printed sample was cut around the cured pattern to obtain bilayer structures of LCE and Ela. v) a 2D precursor stuck on the glass substrate. Hierarchical shape morphing includes the assembly 3D morphing vi) induced by pre‐strain in LCE‐Ela bilayer by releasing the 2D precursor from the glass substrate, and actuation 3D morphing vii) induced by thermal strain in LCE‐Ela bilayer. b) The thermal strain‐temperature curves of the LCE films along directions parallel (D _∥) and perpendicular (D _⊥) to the alignment. c) The stress–strain curves of the LCE films along D _∥ and D _⊥. d) Differential scanning calorimetry measurement of the LCE films. All scale bar: 3 mm.

Figure 3

The effects of pre‐strain and thermal strain magnitude and distribution on the assembly and actuation shapes of the rectangular 2D precursor. a) The fabrication of a rectangular 2D precursor with the pre‐strain direction (blue arrow) and molecular orientation (red arrow) parallel to its longitudinal direction, and its shape at different temperatures. b) Contour plot of the curvature radius (R) in terms of the pre‐strain (ε_P) and thermal strain (ε_T). c) Exp., FEA, and theoretical results of the curvature radius for the arc‐shaped LCE‐Ela structure assembled with different pre‐strains (ε_P =  5%,  10% and 15%) at different temperatures. d) The variation in the curvature radius of the arc‐shaped LCE‐Ela structure under repeated heating (110 °C) and cooling (25 °C). e) The fabrication of three rectangular 2D precursors by printing Ela at different positions of pre‐stretching the LCE substrate along the direction parallel to the alignment (ε_P =  10%), and the FEA and Exp. results of their assembly and actuation shapes. All scale bar: 3 mm.

Figure 4

A design strategy to achieve customizable 3D shape transitions in different directions for the flower‐shaped 3D LCE‐Ela structures. a) The fabrication of a flower‐shaped 2D precursor with eight different pre‐strain directions (blue arrow) and molecular orientations (red arrow), achieved by combining four stretching methods with two printing configurations. b) The design routine, the FEA, and Exp. results of the assembly and actuation shapes of the eight flower‐shaped 2D precursors. All scale bar: 3 mm.

Figure 5

The Exp. results and FEA predictions for the multiple‐curved 3D LCE‐Ela structures formed from the pattern‐designed 2D precursors with varying pre‐strain directions (blue arrow) and molecular orientations (red arrow), as well as the reversible 3D‐to‐3D shape transformations: i) a wing, ii) a manta iii) an ant, iv) a massif, v) a burrito, vi) a palm, vii) a parachute. All scale bar: 5 mm.

Figure 6

Biologically inspired to a proof‐of‐concept biomimetic application of 3D LCE‐Ela structures with dynamically simultaneous deformation and discoloration. a) The 2D precursors of the three biomimetic 3D LCE‐Ela structures, including the chameleon i), butterfly ii), and spider iii), along with their reversible 3D‐to‐3D shape transformations and color changes at different times during heating and cooling. b) Placed these 3D biomimetic structures in a real natural environment to display their adaptive deformation and discoloration, driven by a heating stimulus. c) The 2D precursors i), and shape and color at different temperature of the leaf‐shaped 3D LCE‐Ela structure capable of information encryption and camouflage; ii) The leaf‐shaped 3D LCE‐Ela structure blends with its environment, camouflaging itself, but deforms and discolors when heated to reveal hidden information, returning to its original form and color once the heat was removed. All scale bar: 5 mm.