No dia 10 de fevereiro, o Departamento de Física do ISEL promove o seminário "Spontaneous rotation and propulsion of suspended capsules in active nematics".

O evento, que decorrerá pelas 14h30 no Auditório A, terá como orador Rodrigo Coelho (CBPF - Brazilian Centre for Research in Physics, Rio de Janeiro, Brazil).
 

Abstract:

Active nematics are nonequilibrium fluids composed of self-driven elongated units that continuously inject energy at the microscopic scale, giving rise to spontaneous flows and the emergence of topological defects. When deformable capsules are suspended in such media, the interplay between active stresses, geometry, and elasticity leads to rich and unexpected dynamics.

In this seminar, I will present lattice Boltzmann simulations of elastic capsules immersed in two-dimensional active nematic fluids, focusing on how capsule shape, size, and rigidity control emergent motion.

Circular capsules with active interiors exhibit persistent spontaneous rotation, despite their geometric symmetry, when their size stabilizes a pair of confined +1/2 defects in a rotating yin–yang configuration. In contrast, asymmetric capsules such as boomerangs do not rotate persistently but instead develop directed propulsion along their axis of symmetry, driven by unbalanced active forces generated by defect distributions in the surrounding active nematic.

We further show that capsule flexibility suppresses both rotation and propulsion, as active stresses are dissipated into shape deformations rather than coherent motion. These results highlight topological defects as a key mechanism for motility in soft active matter and suggest design principles for shape-controlled microswimmers and active delivery systems.