Research Topics

Collective phenomena - Active Matter

Active matter represents a vibrant research arena consisting of non-equilibrium systems, such as bacteria, cells and animals. The individual units of these systems self-organize and show fascinating collective phenomena, ranging from clustering and phase separation, as well as spontaneous velocity alignment, spatial velocity correlations and flocking phenomena. This research line aims to discover novel effects and phenomena spontaneously arising in minimal active matter models. This may strengthen our understanding of biological systems as well as guide the engineering of novel materials, for instance showing self-repairing properties.

Reference papers:
i) L. Caprini, U. Marini Bettolo Marconi, A. Puglisi. Physical review letters 124 (7), 078001, 2020. "Spontaneous velocity alignment in motility-induced phase separation".
ii) L. Caprini, H. Löwen. Physical Review Letters 130 (14), 148202, 2023. "Flocking without alignment interactions in attractive active brownian particles".

Vibro-robots - Active granular particles

Vibrobots, i.e. granular robots that vibrate because of internal motors or vibrating plates activated by electromagnetic shakers, represent an experimental system to reproduce and investigate the behavior of active particles. With a combination of experiments and simulations, this project aims to explore novel collective effects arising from the interplay between activity, typical of active matter systems, and dissipative collisions typical of granular particles. This research line has the final goal of engineering novel materials with fascinating properties, ranging from self-assembly and self-repairing.

Reference paper:
L. Caprini, A. Ldov, R.K. Gupta, H. Ellenberg, R. Wittmann, H. Löwen, C. Scholz. Communications Physics 7 (1), 52, 2024. "Emergent memory from tapping collisions in active granular matter".

Stochastic thermodynamics and linear response theory

The theory of stochastic thermodynamics proposes to extend classical thermodynamics to small systems where fluctuations play a crucial role. This leads to the generalization of observables, such as work, heat and entropy production, to systems described by stochastic dynamics. In this field, modern challenges call for theoretical analysis ranging from thermodynamics uncertainty relations to the application of stochastic thermodynamics theory to non-equilibrium systems, such as active matter. With the help of linear response theory and out-of-equilibrium fluctuation-dissipation relations, this may lead to the design of efficient engines based on non-equilibrium principles.

Reference paper:
L. Caprini, U. Marini Bettolo Marconi, A. Puglisi, A. Vulpiani. Journal of Statistical Mechanics: Theory and Experiment 2019 (5), 053203, 2019, "The entropy production of Ornstein–Uhlenbeck active particles: a path integral method for correlations".

Non-reciprocal interacting (odd) systems

Over the past decade, there has been a remarkable surge of interest in the properties of fluids with odd viscosity, solids with odd elasticity, and systems with general odd transport coefficients. These systems do not conserve energy, violate time-reversal symmetry, and remain far from equilibrium. To produce such unusual macroscopic properties, odd materials must consist of out-of-equilibrium microscopic units whose interactions break parity symmetry. Examples include granular systems where transverse pairwise interactions arise from friction, spinning colloids where these forces are induced by the flow field advection generated by particle rotations, and colloidal magnets spun by a magnetic field. This research line aims at exploring the properties of these non-reciprocal systems, unveiling hidden collective effects as well as their behavior in confinement.

Reference paper:
L. Caprini, U. Marini Bettolo Marconi, Preprint arXiv:2407.06837, 2024. "Bubble phase induced by odd interactions".

Active particles in complex environments

Typically, active matter systems move in complex environments: bacteria swim in our stomach and several animals run in random landscapes with several obstacles, food sources or dangerous sites. Understanding how simple active matter models behave in complex environments, perhaps with some degree of viscoelasticity, represents a fundamental research step in active matter. This research line may lead to the development of optimal navigation protocols fundamental for food search applications and exploration problems.

Reference paper:
L Caprini, F Cecconi, A Puglisi, A Sarracino Soft Matter 16 (23), 5431-5438, 2020. "Diffusion properties of self-propelled particles in cellular flows".

Self-propelled colloidal systems

Self-propelled colloids are a prototype system to understand the behavior of active matter. In recent years, these active colloids have been used to reproduce collective phenomena, such as motility-induced phase separation. In addition, recently, the spontaneous assembly of colloidal particles made possible the formation of reconfigurable active molecules that show self-avoidance and self-steering similar to the cells of epithelial tissues. Here, theoretical and numerical investigations are needed to explore the interactions between these active molecules as well as the interaction with obstacles. This analysis may shed light on the behavior of biological systems, such as cells.

Reference paper:
I Buttinoni, L Caprini, L Alvarez, FJ Schwarzendahl, H Löwen, Europhysics Letters 140 (2), 27001, 2022. "Active colloids in harmonic optical potentials".

Page updated

Report abuse