A Mean Field Theory of Phase Transitions Affected by Molecular Interconversion

In this paper, we describe the diffusive and interconversion properties of a symmetric mixture of two different dynamics, characteristic for conserved and non-conserved order parameters, in the presence or absence of an external "source" of interconversion. We show that the interactions of the two competing dynamics of the order parameter (diffusion and interconversion) results in the phenomenon of "phase amplification," when one phase grows at the expense of another one. This phenomenon occurs when the order parameter exhibits even a small probability of non-conserved dynamics, thus breaking the particle conservation law. Also, we show that the addition of a source of interconversion drives the system away from equilibrium and creates the possibility for arrested phase separation - the existence of non-growing (steady-state) mesoscopic phase domains. These steady-state phase domains are an example of a simple dissipative structure. The change of the dynamics from phase amplification to microphase separation can be considered as a nonequilibrium "phase transition" in the dissipative system. The theoretical description is used to describe phase transitions affected by interconversion of an equilibrium and nonequilibrium lattice model.