Making Faces: Universal Inverse Design of Surfaces with Thin Nematic Elastomer Sheets (1710.08485v2)

Abstract: Programmable shape-shifting materials can take different physical forms to achieve multifunctionality in a dynamic and controllable manner. Although morphing a shape from 2D to 3D via programmed inhomogeneous local deformations has been demonstrated in various ways, the inverse problem -- programming a sheet to take an arbitrary desired 3D shape -- is much harder yet critical to realize specific functions. Here, we address this inverse problem in thin liquid crystal elastomer (LCE) sheets, where the shape is preprogrammed by precise and local control of the molecular orientation of the liquid crystal monomers. We show how blueprints for arbitrary surface geometries as well as local extrinsic curvatures can be generated using approximate numerical methods. Backed by faithfully alignable and rapidly lockable LCE chemistry, we precisely embed our designs in LCE sheets using advanced top-down microfabrication techniques. We thus successfully produce flat sheets that, upon thermal activation, take an arbitrary desired shape, such as a face. The general design principles presented here for creating an arbitrary 3D shape will allow for exploration of unmet needs in flexible electronics, metamaterials, aerospace and medical devices, and more.

• The paper presents a novel numerical algorithm that preprograms thin LCE sheets to transform into complex 3D forms when heated.
• It employs precise microfabrication and controlled nematic director field alignment to match desired surface metrics with high accuracy.
• The approach paves the way for practical applications in flexible electronics, soft robotics, and medical devices by enabling scalable shape transformation.

Universal Inverse Design of Surfaces with Liquid Crystal Elastomer Sheets

This paper, authored by Hillel Aharoni et al., presents an exploration into the inverse design problem associated with the programmability of thin liquid crystal elastomer (LCE) sheets. The paper meticulously unravels the challenge of designing 2D planar sheets capable of morphing into any desired 3D shape upon thermal activation. This capability represents a substantial advancement in materials science, specifically in utilizing LCEs for dynamic shape transformations.

Core Contributions

The paper's primary innovation lies in addressing the inverse problem of shape morphing in LCE sheets, which involves preprogramming the sheets to attain specific 3D shapes. At the heart of this research is the use of advanced numerical methods to generate blueprints for arbitrary surface geometries and extrinsic curvatures by precisely controlling the molecular orientation of liquid crystal monomers in LCEs.

The authors employed top-down microfabrication techniques, allowing for accurate alignment and rapid locking of the LCE's molecular structure. Through this approach, flat sheets could transform into complex 3D shapes, such as faces, when heated. The numerical approach involved solving for a planar nematic director field that aligns with the desired metric tensor of the sheet, dictating its 3D form post-deformation.

Experimental Methodology

This work demonstrates a rigorous experimental framework. Initially, the authors designed a numerical algorithm capable of approximating solutions to the inverse design problem, taking into account the anisotropic material deformations at target temperatures. The implementation involved creating a spatially variant nematic director field using a novel surface alignable LCE chemistry via an oxygen-mediated thiol-acrylate reaction. This chemistry circumvented traditional LCE issues with oxygen sensitivity, leading to a uniform distribution of strain within the films.

Notably, the experimental setup utilized direct laser writing to pattern molds at microscale resolution, ensuring precise orientation control of the nematic director across the LCE sheet. The realization of complex geometries such as constant Gaussian curvature surfaces and leaf shapes attested to the effectiveness of these methodologies.

Numerical Algorithm and Theoretical Implications

The mathematical foundations laid out in the paper draw heavily on earlier theories that relate to nematic elastomer sheet deformations. The algorithm iteratively adjusted parameterizations within a mesh to achieve the desired metric tensor properties. The results evidenced by the experiments not only validate the mathematical model but also highlight the necessary considerations for accurate deformation predictions in practical applications.

The incorporation of a curvature gradient across the sheet's thickness presents another layer of sophistication, aiding in guiding the sheets through various potential isometric configurations.

Applications and Future Directions

The implications of this research extend broadly across fields such as flexible electronics, medical devices, and soft robotics. The ability to produce complex 3D shapes from 2D sheets using LCEs with predefined thermal responses could revolutionize manufacturing processes across these industries. Future work will likely focus on enhancing the precision of director field alignment, expanding the control over curvature, and integrating this technology into composite systems for wider applicability.

The transition from theoretical constructs to practical fabrication in this research underscores a pivotal step toward advanced programmable materials. Further exploration and optimization in this domain are anticipated to significantly broaden the scope of applications that can benefit from deployable LCE-based structures.