The field of active matter, characterized by particles that utilize environmental energy to self-propel, bridges multiple scientific areas, from biology to physics to engineering [53]. In groups, these inherently out-of-equilibrium systems will show complex collective behaviors that are not understood by the sum of their parts [28][5]. This thesis studies the dynamics of capsules in active nematic systems, using an Immersed-Boundary-Lattice-Boltzmann method (IB-LBM). We explore the impact of the capsule’s shape, size, and flexibility on its dynamics. Additionally, we briefly explore the impact of the substrate friction on the capsule’s dynamics. We found friction to be a deciding factor in the capsule (and tracer) dynamics: for high friction, we observe a long-time diffusive regime; and for low friction, we observe a long-time superdiffusive regime. We focused on the high friction scenario, where we found that the capsule’s size inversely correlates with diffusion rate, with smaller capsules having a faster transport. The shape has an important role, as circular capsules diffuse faster than triangular capsules. Most notably, asymmetric capsules displayed a long-time superdiffusive regime and a strong preferential direction of motion. Flexibility has a significant impact on highly flexible capsules, that adopt finger-like shapes and exhibit a long-time diffusive regime with a slower diffusion and two preferential directions of motion, along the length of the finger-like shape. We concluded that the anomalous transport, in the high friction scenario, was connected to the nematic texture around the capsule, due to the anchoring. In future work, we intend to explore the dynamics further in the high friction scenario, with particular attention to the rotational dynamics. Additionally, we want to study the low friction scenario.

Tese de mestrado, Física (Física Estatística e Matéria Condensada), 2025, Universidade de Lisboa, Faculdade de Ciências