Transport phenomena are fundamental and irreversible processes that occur due to the random motion of particles in condensed and gas phases of matter out of equilibrium, according to the second law of thermodynamics. The exchange of quantities such as energy, charge, and mass between different domains of a system is characterised and quantified, in the linear response regime, by transport coefficients, such as thermal and electrical conductivities, diffusivity, etc., which represent the proportionality factor between an external “thermodynamic force” (like a gradient of temperature, electrical potential or concentration) and the induced flux of heat, charge, or particles of a given type.
Transport phenomena are ubiquitous in material science and technology, influencing the efficiency of devices, fuel cells, heat exchangers: for instance, in the current quest for solid-state electrolytes for next generation batteries, a tradeoff between the flow of ionic charge - needed for fast charging and large powers - and a safe Joule-heat dissipation must be found to avoid overheating or explosions. The ability to understand, and then tune, materials’ transport properties is thus of paramount importance for next future technological development with vast societal impact.
From a more speculative standpoint, transport properties play a crucial role also in planetary science, where they govern the behaviour of materials at the extreme conditions typical of the interior of celestial bodies, allowing to construct evolutionary models of planets able to explain their current characteristics, like their temperature profile, luminosity or electromagnetic fields.
Despite their significance in different branches of physical, chemical, and materials sciences, as well as in their applications, our understanding of transport coefficients, including their dependence on microscopic chemical composition, pressure, and temperature, remains incomplete. Moreover, the experimental measurement of transport properties is often challenging for novel materials in the energy and industrial sectors, hazardous substances, or systems in extreme geophysical conditions.
Therefore, the development of accurate theories and numerical simulations, that account for the quantum nature of particles and interactions among them, is not only a subject of scientific speculation but also serves a practical purpose in predicting and tailoring properties that would otherwise be inaccessible. This action aimed to achieve fundamental advancements in this research domain, with a specific emphasis on ionic liquids and systems, like superionic materials, characterised by the presence of at least a diffusive species.
