Why leaves curl with water content varied: Mechanics can illustrate biology

The phenomenon of plant leaves curling in the dehydration or water absorption process is normally observed in our daily life. In this study, we show that a simple mechanics model can be used to uncover the mechanism of this deformation. In consideration of the nonuniformly distributed tissues, a leaf is abstracted as a composite beam including two layers. We then derive the expression of the neutral axis curvature due to the mismatch strain, which shows that it is just the different capabilities to conduct water for the two layers that result to this curling deformation. Our experiment on the deformation of a composite sheet in water sucking verifies this theoretical model. These investigations may cast new light on how to design humidity-mediated sensors or actuators and are beneficial to illustrate the curved morphologies of some plant structures in nature.

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