Mechanics and geometry of nematic shape-morphing sheets

Résumé :

Thin ‘shape-programmed’ sheets morph into curved shapes when stimulated by heat, light, or chemical fuel. Biology is full of intricate examples (leaves, petals, etc), and soft synthetic materials such as liquid-crystal elastomers have begun to approach similar levels of richness, opening doors to bio-inspired soft machines. Such machines can lift, pump, push, pull, . . . etc, promising myriad applications including microfluidic components, deployable structures, switchable surfaces, and robotic actuators. I’ll present work on nematic shape morphers, in which the direction of anisotropic deformation is patterned, while deformation magnitudes are spatially uniform. The focus will be on encoding Gauss curvature, which imparts mechanical strength to the resultant structures, as Gauss understood centuries ago. The patterned deformation direction must typically be chosen at the time of manufacture, leading to a design limitation: the morphing sheet can only realise a single target shape. I will then show how to overcome this limitation, by varying the deformation magnitude (e.g. via patterned illumination) in both space and time. This new paradigm allows a single physical sample to be morphed into arbitrarily many different shapes at will. Thus a designer can specify entire time-dependent motions of the sheet. This capability could greatly increase the versatility of soft robots, e.g. when operating in confined environments or performing complex tasks. Furthermore, it facilitates swimming, which typically requires non-reciprocal motion. More generally, it unlocks the full potential of shape-morphing sheets, allowing them to progress from being merely functional to being truly multi-functional.

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Contact : emmanuel.siefert@univ-grenoble-alpes.fr