Calorimetry for active systems

TL;DR

This paper develops a theoretical framework for calorimetry in active particle systems, using simulations to explore heat capacity behavior and identify activity-related phenomena like peaks and negative values.

Contribution

It introduces a theoretical basis for calorimetry in active particles and demonstrates how heat capacity measurements can reveal activity and phase transitions.

Findings

Heat capacity exhibits Schottky-like peaks at low temperatures.

Negative heat capacity regimes occur at high propulsion speeds.

Heat capacity increases significantly at low temperatures in active systems.

Abstract

We provide the theoretical basis of calorimetry for a class of active particles subject to thermal noise. Simulating AC-calorimetry, we numerically evaluate the heat capacity of run-and-tumble particles in double-well and in periodic potentials, and of systems with a flashing potential. Low-temperature Schottky-like peaks show the role of activity and indicate shape transitions, while regimes of negative heat capacity appear at higher propulsion speeds. From there, a significant increase in heat capacities of active systems may be inferred at low temperatures, as well as the possibility of diagnostic tools for the activity of self-motile artificial or biomimetic systems based on heat capacity measurements.