Light-induced shape morphing of thin films

Abstract

Shape transformation of thin two-dimensional sheets into three-dimensional structures using light is of great interest for remotely-controlled fabrication, surface modulation, and actuation. Over the last few decades, significant efforts have been made to develop materials systems incorporating photochemical or photothermal elements to drive deformation in response to illumination. However, the full extent of the interplay between chemistry, optics, and mechanics in these materials is poorly understood. In this Review, we introduce principles of shape morphing in these systems by considering the underlying physics of photo-induced stresses and how these have been used in recent literature. In addition, we provide a critical overview of the important design characteristics of both photochemical and photothermal system and offer our view on the open opportunities and challenges in this rapidly growing field.

Blueprinting Photothermal Shape‐Morphing of Liquid Crystal Elastomers

“…[ 1 ] Over the past decade, numerous studies have focused on programming desired 3D structures of soft materials such as shape‐memory polymers [ 2,3 ] and gels [ 4–7 ] by introducing spatial variations in thermal expansion/contraction, swelling, or molecular order. [ 8 ] A particularly useful class of materials to achieve dynamic 2D to 3D shape transformations are liquid crystal elastomers (LCEs), where the coupling between the orientational ordering of polymerized mesogens and the conformation of a polymer backbone can be leveraged for large, anisotropic deformations that are dictated by the director field. [ 9,10 ] Using oriented surface alignment layers [ 11 ] or microchannels, [ 12 ] director orientation can be patterned with a resolution approaching 10 µm.…”

“…Furthermore, light‐responsive systems are particularly useful for programming deformation profiles, either through spatiotemporally patterned light fields or flood illumination of materials containing localized inclusions of photothermal or photochemical moieties. [ 8 ] Programmed buckling in response to both patterned and flood illumination has been widely exploited in gel [ 30–32 ] and shape‐memory polymer systems. [ 33–36 ] In contrast, work on liquid crystalline materials has focused primarily on the use of spatially patterned light [ 37–40 ] with a few exceptions including azobenzene‐containing LCEs with shapes blueprinted by director orientation [ 41 ] and glassy LC polymer cantilevers with coarsely patterned photothermal hinges.…”

Reconfiguring Gaussian Curvature of Hydrogel Sheets with Photoswitchable Host–Guest Interactions

“…While photothermal moieties such as carbon materials 17 − 19 and gold nanoparticles 20 − 25 have been exploited for photopatterned deswelling of thermoresponsive gels, the use of photochemical additives would offer advantages in terms of shape persistence and improved patterning resolution, due to the absence of thermal broadening and heat dissipation inherent to photothermal responses. 26 Though photochemically addressable hydrogel systems are predicted to enable robust reconfigurable shape change, 27 , 28 experimental demonstrations have been limited. The most promising approach to date has relied on spiropyran derivatives, where photoreversible ring-opening and -closing reactions drive large changes in hydrophilicity and thus swelling.…”

Instabilities in liquid crystal elastomers

“…Nevertheless, a better understanding of these materials is needed before they can be exploited on an industrial scale. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] Since the early discovery of liquid crystalline solids, probing their intriguing material properties has been the focus of research laboratories around the world, and the importance of such essential work is hard to overstate. However, their accurate description can only be useful if fully integrated in a multiphysics framework combining elasticity and liquid crystal theories.…”