arXiv subjects

Ioannis Hadjifrangiskou

Publications and source records attributed to Ioannis Hadjifrangiskou.

5 recordsLinked to original sources

arXiv2026

Active flows drive anchoring of nematics at rigid walls

Although confinement strongly influences flows in active materials, it remains unclear how active particles align at rigid boundaries when no thermodynamic anchoring is imposed. We address this question using continuum simulations of active nematics, together with analytical arguments based on a reduced near-wall description. In the flow-tumbling regime, extensile systems align parallel to the boundary, whereas contractile systems align perpendicular to it, consistent with active anchoring observed at active-passive interfaces. In the flow-aligning regime, the preferred orientation depends on the sign of activity and of the flow aligning parameter: either the shear-like flow generated near the wall selects the Leslie angle, or no unique alignment is established. These results provide a unified framework for activity-induced anchoring at rigid walls, demonstrating that boundary alignment in dense active matter can emerge solely from the interplay between self-generated flows and orientational dynamics.

cond-mat.soft↗

arXiv2026

Shear-Induced Collective Shape Oscillations in Dense Soft Suspensions

Dense suspensions of deformable particles can exhibit rich nonequilibrium dynamics arising from complex flow-structure coupling. Using a multi-phase field model, we show that steady shear drives an initially disordered, dense, soft suspension into a positionally and orientationally ordered state, within which particles undergo robust self-sustained shape oscillations. These oscillations originate from repeated T1 neighbor exchanges that force the ordered particle lattice to cyclically traverse different ordered configurations, coupling particle deformation to evolving lattice topology. By identifying the lattice angle as a key variable, we construct a minimal one-degree-of-freedom model that quantitatively captures the limit cycle oscillation. Because these mechanisms rely only on deformability, packing, and shear, they provide a generic route to collective time-dependent behavior in dense soft suspensions.

cond-mat.soft↗

arXiv2025

Channel flows of deformable nematics

We describe channel flows in a continuum model of deformable nematic particles. In a simple shear flow, deformability leads to a nonlinear coupling of strain rate and vorticity, and results in shape oscillations or flow alignment. The final steady state can depend on initial conditions, and we explain this behaviour by considering a phase space representation of the dynamics. In Poiseuille flow, particle deformability and nematic elasticity induce banding, where particles near the walls are aligned, and those near the centre of the channel oscillate in direction and shape. Our results show that particle deformability can lead to complex behaviour even in simple flows, suggesting new microfluidic experiments.

cond-mat.soft↗

arXiv2025

Nematic order from phase synchronization of shape oscillations

We show that a suspension of non-interacting deformable particles subjected to an oscillatory shear flow leads to development of nematic order that arises from the phenomenon of phase synchronization. The synchronized state corresponds to a unique, stable limit cycle confined in the toroidal state space. The limit cycle exists since, unlike rigid particles, deformable particles can modulate aspect ratio, adjust their tumbling rate and thus, achieve phase synchronization. These synchronized regions emerge as Arnold tongues in the parameter-space of the driving amplitude and frequency. Considering the rheological implications of ordering dynamics in soft and active matter, our results motivate oscillatory shear flow experiments with deformable particles.

cond-mat.soft↗

arXiv2023

Active nematics with deformable particles

The hydrodynamic theory of active nematics has been often used to describe the spatio-temporal dynamics of cell flows and motile topological defects within soft confluent tissues. Those theories, however, often rely on the assumption that tissues consist of cells with a fixed, anisotropic shape and do not resolve dynamical cell shape changes due to flow gradients. In this paper we extend the continuum theory of active nematics to include cell shape deformability. We find that circular cells in tissues must generate sufficient active stress to overcome an elastic barrier to deforming their shape in order to drive tissue-scale flows. Above this threshold the systems enter a dynamical steady-state with regions of elongated cells and strong flows coexisting with quiescent regions of isotropic cells.

cond-mat.soft↗