Feedback between chemical reactions and physical interactions plays a central role in the self-organization of biomolecules within living cells.  For example, intracellular protein/RNA droplets that form spontaneously can modify the spatial distribution of enzymes and metabolites and thus shape metabolic pathways [1].  At the same time, chemical reactions can also tune the driving forces for phase separation and thus alter the landscape for biomolecular condensate formation [2].  Most interestingly, when reactive fluxes are spatially inhomogeneous and driven out of equilibrium by a chemical fuel source, such as ATP, exciting new physics can emerge [3, 4].  Such “chemically active” mixtures can exhibit arrested coarsening, in which phase-separated droplets cease to grow at a length scale determined by nonequilibrium reactive fluxes [5]; tunable surface tensions, in which nonequilibrium reactions modify the fluctuations at phase-separated interfaces [6]; and droplet motility, in which phase-separated droplets swim along concentration gradients at steady state [7, 8].  These inherently nonequilibrium features have crucial implications for droplet size selection [3, 5], nucleation dynamics [6, 9, 10], and pattern formation [11, 12] in living cells.  Exciting efforts are also underway to engineer these features in synthetic soft matter systems [13, 14, 15], with the ultimate goal of developing de novo protocells [16] and bioreactors [17, 18].

Despite the intense interest in this topic over the past few years, fundamental theoretical and computational challenges remain unsolved.  A wide variety of simulation models have been proposed, which treat nonequilibrium reactions and many-body effects at different scales and coarse-graining resolutions [19].  Building on a rich tradition of continuum-level reaction-diffusion models, active Cahn–Hilliard and sharp-interface models [3, 5, 9] have been developed to study droplet size selection and pattern formation.  Related approaches that incorporate hydrodynamic effects [20] have also been introduced to study droplet motility.  By contrast, microscopic simulation models have been utilized to study fluctuations at finer scales [6, 21, 22, 23].  As these methods differ in their treatment of irreversibility and microscopic fluctuations, it is not surprising that they have not always arrived at consistent predictions.  Moreover, parallel advances taking place theoretically, in terms of nonequilibrium statistical mechanics and stochastic thermodynamics [24, 25], and experimentally, with the development of new platforms for testing theoretical predictions [7, 15], need to be reconciled and integrated with these modeling approaches.  It is therefore an opportune time to address how these multiscale modeling strategies interface with one another and with state-of-the-art experiments.

The key emphasis of the workshop will be on bridging theoretical and computational approaches at different scales [26, 27], with a focus on thermodynamically consistent treatments of nonequilibrium reactions, many-body effects [28, 29], and microscopic fluctuations.  This workshop will address these gaps in existing theoretical treatments and stimulate the development of improved computational methods to advance the exciting science of chemically active mixtures.