arXiv subjects

Jose Martin-Roca

Publications and source records attributed to Jose Martin-Roca.

3 recordsLinked to original sources

arXiv2026

How Phase Coexistence affects the mechanical properties of heterogeneous 2D suspensions

Although numerical simulations of rheological measurements typically focus on homogeneous systems, heterogeneity can profoundly impact material properties. We report on the rheological properties of a suspension of two-dimensional Lennard-Jones particles across the gas/liquid and the gas/solid coexistence lines of the system. We show how the presence of multiple coexisting states has a significant impact on the mechanical properties of these systems when compared with their homogeneous reference counterparts. Our results establish an extended map to navigate a landscape where not only density and temperature, but also phase coexistence, dictate the transition from viscous to elastic-dominated behavior under shear. These results provides a benchmark for future research into heterogeneous fluids where the coexistence of complex dynamic states is frequently observed.

cond-mat.soft↗

arXiv2022

Simulating active agents under confinement with Dissipative Particles (hydro)Dynamics

We study active agents embedded in bulk or in confinement explicitly considering hydrodynamics and simulating the swimmers via an implementation inspired by the squirmer model. We develop a Dissipative Particle Dynamics scheme for the solvent. This approach allows us to properly deal not only with hydrodynamics but also with thermal fluctuations. On the other side, this approach enables us to study active agents with complex shapes, ranging from spherical colloids to polymers. To start with, we study a simple spherical colloid. We analyze the features of the velocity fields of the surrounding solvent, when the colloid is a pusher, a puller or a neutral swimmer either in bulk or confined in a cylindrical channel. Next, we characterise its dynamical behaviour by computing the mean square displacement and the long time diffusion when the active colloid is in bulk or in a channel (varying its radius) and analyze the orientation autocorrelation function in the latter case. While the three studied squirmer types are characterised by the same bulk diffusion, the cylindrical confinement considerably modulates the diffusion and the orientation autocorrelation function. Finally, we focus our attention on a more complex shape: an active polymer. We first characterise the structural features computing its radius of gyration when in bulk or in cylindrical confinement, and compare to known results obtained without hydrodynamics. Next, we characterise the dynamical behaviour of the active polymer by computing its mean square displacement and the long time diffusion. On the one hand, both diffusion and radius of gyration decrease due to the hydrodynamic interaction when the system is in bulk. On the other hand, the effect of confinement is to decrease the radius of gyration, disturbing the motion of the polymer and thus reducing its diffusion.

cond-mat.soft↗

arXiv2022

Dynamical anomalies and structural features of Active Brownian Particles characterised by two repulsive length scales

In this work we study a two-dimensional system composed by Active Brownian Particles (ABPs) interacting via a repulsive potential with two-length-scales, a soft shell and a hard-core. Depending on the ratio between the strength of the soft shell barrier and the activity, we find two regimes: If this ratio is much larger or smaller than 1, the observed behaviour is comparable with ABPs interacting via a single length-scale potential. If this ratio is similar to 1, the two length-scales are relevant for both structure and dynamical properties. On the structural side, when the system exhibits a motility induced phase separation, the dense phase is characterised by new and more complex structures compared with the hexatic phase observed in single length-scale systems. On the dynamical side, as far as we are aware, this is the first representation of an anomalous dynamics in active particles.

cond-mat.soft↗