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Formation of desired three-dimensional (3D) shapes from flat thin sheets with programmed non-uniform deformation profiles is an effective strategy to create functional 3D structures. Liquid crystal elastomers (LCEs) are of particular use in programmable shape morphing due to their ability to undergo large, reversible, and anisotropic deformation in response to a stimulus. Here we consider a rectangular monodomain LCE thin sheet divided into one high- and one low-temperature strip, which we dub a ‘bistrip’. Upon activation, a discontinuously patterned, anisotropic in-plane stretch profile is generated, and induces buckling of the bistrip into a rolled shape with a transitional bottle neck. Based on the non-Euclidean plate theory, we derive an analytical model to quantitatively capture the formation of the rolled shapes from a flat bistrip with finite thickness by minimizing the total elastic energy involving both stretching and bending energies. Using this analytical model, we identify the critical thickness at which the transition from the unbuckled to buckled configuration occurs. We further study the influence of the anisotropy of the stretch profile on the rolled shapes by first converting prescribed metric tensors with different anisotropy to a unified metric tensor embedded in a bistrip of modified geometry, and then investigating the effect of each parameter in this unified metric tensor on the rolled shapes. Our analysis sheds light on designing shape morphing of LCE thin sheets, and provides quantitative predictions on the 3D shapes that programmed LCE sheets can form upon activation for various applications.
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Multiple shapes from a single nematic elastomer sheet activated via patterned illumination
Abstract Liquid crystal elastomers (LCEs) undergo a large uniaxial contraction upon thermal or optical stimulation. LCE sheets are often fabricated with a spatially patterned direction of contraction, which can sculpt the sheet into a Gauss-curved surface. Here, we instead consider LCE sheets subject to patterned stimulation intensity, leading to a control of contraction strength. We show such patterns may also sculpt a complex surface, but with the advantage that arbitrarily many surfaces may be achieved sequentially in the same sample, thus breaking the link between microstructure and shape. We first consider a monodomain LCE in which some regions are actuated and others are not. We discuss how to join actuated and unactuated regions compatibly, and use this design rule to generate patterns for cones, anti-cones, arrays of cones and a rolling bi-strip. We validate the patterns numerically via elastic shell simulations and demonstrate them experimentally via patterned photo-chemical actuation. Secondly, we consider an LCE disk with an azimuthal director profile actuated by a radially varying stimulus. We show, theoretically and numerically, how to design a stimulation profile to sculpt any surface of revolution. Such re-configurable actuation offers enticing possibilities for haptics, robotics and locomotion.
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- Award ID(s):
- 1921842
- PAR ID:
- 10440858
- Date Published:
- Journal Name:
- Europhysics Letters
- Volume:
- 140
- Issue:
- 3
- ISSN:
- 0295-5075
- Page Range / eLocation ID:
- 36003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1209/0295-5075/ac9e19
