arXiv subjects

Lucas H. P. Cunha

Publications and source records attributed to Lucas H. P. Cunha.

3 recordsLinked to original sources

arXiv2026

Hydrodynamic cascade drives tumbling in sheared colloidal rod suspensions

Modeling the dynamics of colloidal rods remains a central challenge in soft-matter physics due to the anisotropic and long-ranged nature of their interactions. Hydrodynamic interactions in rods suspensions are often assumed to be screened or too week to play any role in semi-dilute regimes, yet we find here these assumptions to break down at shear rates and concentrations that are often attained in experiments. Using particle-based simulations and scaling analysis, we uncover a cascade of tumbling events driven by hydrodynamic coupling among neighboring rods. This collective dynamics disrupts flow alignment and leads to a pronounced increase in viscosity and normal stress differences, in qualitative agreement with recent experiments. The discovery of this hydrodynamically-promoted cascade effect calls for a revision of existing constitutive models for colloidal rods and highlights hydrodynamic coupling as a key mechanism governing collective dynamics in highly anisotropic suspensions.

cond-mat.soft↗

arXiv2026

Interaction potentials for mutually induced dipoles in uniform fields

Dipolar interactions govern the structure and dynamics of many soft-matter systems, from molecular to colloids assemblies. When dipole moments are induced by an external field, mutual interactions lead to a many-body magnetization response that cannot be described by fixed-dipole models. Here, we derive the interaction potential for a system of mutually interacting induced dipoles in a uniform external field using a force-based approach. By accounting for the displacement-induced variation of the dipole moments, we obtain an interaction potential consisting of the classical dipole-dipole term supplemented by two- and three-body corrections arising from mutual induction. Comparisons with simplified models that neglect mutual magnetization reveal significant errors in the interaction potential, particularly in anisotropic particle assemblies. We also discuss an efficient $\mathcal{O}(N^2)$ iterative scheme for computing the mutual magnetization, enabling accurate simulations of large dipolar systems.

cond-mat.soft↗

arXiv2024

Capturing the slow relaxation time of superparamagnetic colloids in time-varying fields

Superparamagnetic colloids present interesting assembly dynamics and propulsion in time-varying magnetic fields due to their magnetic relaxation. However, little is known about the mechanisms governing this magnetic relaxation, which is commonly attributed to the interactions and polydispersity of the ferromagnetic nanoparticles distributed within the colloid. We measure this relaxation from the effective potential between colloids subjected to rotating magnetic fields. Remarkably, our results indicate the presence of magnetic relaxation times much longer than what has been reported, which furthers our understanding of the magnetization of colloids in complex magnetic fields.

cond-mat.soft↗