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Shape programming lines of concentrated Gaussian curvature

Accepted version
Peer-reviewed

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Article

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Abstract

Liquid crystal elastomers (LCEs) can undergo large reversible contractions along their nematic director upon heating or illumination. A spatially patterned director within a flat LCE sheet thus encodes a pattern of contraction on heating, which can morph the sheet into a curved shell, akin to how a pattern of growth sculpts a developing organism. Here we consider, theoretically, numerically and experimentally, patterns constructed from regions of radial and circular director, which, in isolation, would form cones and anticones. The resultant surfaces contain curved ridges with sharp V-shaped cross-sections, associated with the boundaries between regions in the patterns. Such ridges may be created in positively and negatively curved variants and, since they bear Gauss curvature (quantified here via the Gauss-Bonnet theorem), they cannot be flattened without energetically prohibitive stretch. Our experiments and numerics highlight that, although such ridges cannot be flattened isometrically, they can deform isometrically by trading the (singular) curvature of the V angle against the (finite) curvature of the ridge line. Furthermore, in finite thickness sheets, the sharp ridges are inevitably non-isometrically blunted to relieve bend, resulting in a modest smearing out of the encoded singular Gauss curvature. We close by discussing the use of such features as actuating linear features, such as probes, tongues and limbs, and highlighting the similarities between these patterns of shape change and those found during the morphogenesis of several biological systems.

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Keywords

cond-mat.soft, cond-mat.soft

Journal Title

Journal of Applied Physics

Conference Name

Journal ISSN

0021-8979
1089-7550

Volume Title

129

Publisher

AIP Publishing

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All rights reserved
Sponsorship
MRC (MR/S017186/1)
Engineering and Physical Sciences Research Council (EP/P034616/1)
Engineering and Physical Sciences Research Council (EP/L015552/1)
F.F. and M.W. were supported by the EPSRC [grant number EP/P034616/1]. M.W. is grateful for support from the ELBE Visiting Faculty Program, Dresden. D.D. was supported by the EPSRC Centre for Doctoral Training in Computational Methods for Materials Science [grant no. EP/L015552/1]. J.S.B. was supported by a UKRI “future leaders fellowship” [grant number MR/S017186/1]. This material is partially based upon work supported by the National Science Foundation under Grant DMR 2041671.