Tuning nucleation kinetics via nonequilibrium chemical reactions

Unlike fluids at thermal equilibrium, biomolecular mixtures in living systems can sustain nonequilibrium steady states, in which active processes modify the conformational states of the constituent molecules. Despite qualitative similarities with liquid-liquid phase-separation at thermal equilibrium, the extent to which the phase-separation kinetics differ in nonequilibrium steady states remains unclear. Here we consider the influence of driven chemical reactions, which couple molecular conformational changes to a chemical fuel source. We show that driven chemical reactions can alter the nucleation kinetics of liquid-liquid phase separation in a manner that is consistent with classical nucleation theory, but can only be rationalized by introducing a nonequilibrium interfacial tension. We demonstrate that deviations from equilibrium kinetics arise when the chemical reactions are driven inhomogeneously between the phases, leading to different effective thermodynamics on either side of the interface. Finally, we identify conditions under which nucleation can be accelerated without changing the energetics or supersaturation, thus breaking the correlation between fast nucleation and strong driving forces that is typical of phase separation and self-assembly at thermal equilibrium.