Chantal Valeriani

Fluid phase equilibrium depends on the external constraints imposed on a system. In a closed system with fixed volume, depending on the average density, a vapor bubble may be stable, metastable, or unstable, with respect to the homogeneous liquid phase. In the case where the bubble is metastable, we study its lifetime, i.e., the average waiting time needed to observe bubble collapse, and the corresponding lifetime of the homogeneous liquid. For the smallest systems, we predict the possibility to observe phase flipping, when the fluid oscillates between states with and without bubble. We provide an example of phase flipping in a simulation of a Lennard-Jones fluid.

We present a tunable mesoscale model to provide a basis for future rheologicalcalculations of of bacterial biofilms, explicitly incorporating reversiblecrosslinking within the extracellular polymeric substance (EPS) matrix. Usinga Dissipative Particle Dynamics framework combined with a Gillespieinspiredalgorithm, bonds between polymers and bacteria dynamically formand break, capturing the intrinsically evolving nature of the network. Weshow that biofilm structure is governed by a competition between polymer–polymer and polymer–bacteria crosslinks, controlled by binding energy,linker availability, and bond stiffness and provide a minimal model that helpsto understand the competition between both species.

Robophysics investigates the physical principles that govern living-like robots operating in complex, real-world environments. Despite remarkable technological advances, robots continue to face fundamental efficiency limitations. At the level of individual units, locomotion remains a challenge, while at the collective level, robot swarms struggle to achieve shared purpose, coordination, communication, and cost efficiency. This perspective article examines the key challenges faced by bio-inspired robotic collectives and highlights recent research efforts that incorporate principles from active-matter physics and biology into the modeling and design of robot swarms.

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.

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.

Collective motion is ubiquitous in active systems at all length and time scales. The mechanisms behind such collective motion are usually alignment interactions between active particles, effective alignment after collisions between agents, or symmetry-breaking fluctuations induced by passive species in active suspensions. In this article, we introduce a new type of collective motion in the shape of a traveling band induced purely by confinement, where no explicit or effective alignment is prescribed among the active agents. We study a suspension of run-and-tumble particles confined in microchannels comprising asymmetric boundaries: one flat wall and one array of funnel-like obstacles. We study the phase behavior of the confined active suspension upon changes in the packing fraction and persistence length to define the stability region of the traveling band. We characterize the traveling band structurally and dynamically and study its stability with respect to the geometry of the microchannel. Finally, we describe the mechanism of motion of the band, which resembles the tracked locomotion of some heavy vehicles such as tractors, finding that a counter-flux of active particles in the lower part of the band, explained in terms of source–sink and vacancy diffusion mechanisms, is the facilitator of the traveling band and sustains its motion. We name this new collective phenomenon confinement-induced tracked locomotion.

Water shows numerous thermodynamic, dynamic, and structural anomalies. Recent experiments [Eichler et al., Phys. Rev. Lett. 134, 134101 (2025)], based on measurements of shear and bulk viscosities of liquid water up to 1.6 GPa, have reported the existence of a minimum in the variation of the structural relaxation time τα with pressure at room temperature. Here, we investigate this and related properties with molecular dynamics simulations of the TIP4P/2005 water model, performed at extreme pressures commensurate with the experiments. Specifically, we compute dynamic (self-diffusion, shear and bulk viscosities, and structural relaxation time) and structural (oxygen–oxygen radial distribution function, structure factor, and translational order parameter) properties down to 220 K and up to 2.7 GPa. We find good agreement with the experimental observations and confirm the existence of a minimum in τα. The microscopic information obtained from the simulations suggests that this anomaly is related to the sudden reorganization of the hydrogen bond network induced by pressurization.

We report an approach to obtain effective pair potentials which describe the structure of two-dimensional systems of active Brownian particles. The pair potential is found by an inverse method, which matches the radial distribution function found from two different schemes. The inverse method, previously demonstrated via simulated equilibrium configurations of passive particles, has now been applied to a suspension of active particles. Interestingly, although active particles are inherently not in equilibrium, we still obtain effective interaction potentials which accurately describe the structure of the active system. Treating these effective potentials as if they were those of equilibrium systems, furthermore allows us to measure effective chemical potentials and pressures. Both the passive interactions and active motion of the active Brownian particles contribute to their effective interaction potentials.