ESPCI web site
Shell deformation and swimming
A spherical hollow object, isotropic and homogeneous at the scale of its radius (micronic in various examples to be found in Soft Matter, biology, or in miniaturized devices) is likely to present a diversity of shapes when its volume is decreased. Such an object being fruitfully modelled by a closed elastic surface, the role of the 2D parameters on the shapes will be discussed, as well as their correlation with the tridimensional nature of the modelled object. In this framework, the knowledge of the deformation modes of a shell submitted to a deflation/re-inflation cycle allowed to propose a new kind of microswimmers, that would be robust, possibly synthesized with high throughput, and powered by a scalar field : spherical colloidal shells full of air, actionned through sound or ultrasonic waves. The contraction of a spherical shell happens via a buckling instability toward an axisymmetrical shape, and its roll-out back to the spherical initial state occurs through a succession of shapes unexplored during the deflation : one then expects that pressure cycles generate a net displacement, even if inertia is negligible. In order to study the swimming of such an object, we realized an upscaling where adimensional numbers of interest are conserved. The first results allows to quantify the flows during the deformation of the shell, to get the order of magnitude of the thrust, and to forecast the consequences of dissipation on the material during rapid deformations.