  This paper concerns modeling of the evolution of intermittency region between
two weakly miscible phases due to temporal and spatial variations of its
characteristic length scale. First, the need of a more general description
allowing for the evolution of intermittency region is rationalized. Afterwards,
results of the previous work (Wac{\l}awczyk T., 2017, On a relation between the
volume of fluid, level-set and phase field interface models, Int. J. Multiphas.
Flow, Vol. 97) are discussed in context of the sharp interface models known in
the literature and insight into droplet coalescence mechanism recently
recognized in the molecular dynamics studies (Perumanath S., Borg M.K.,
Chubynsky M.V., Sprittles J.E., Reese J.M., 2019, Droplet coalescence is
initiated by thermal motion, Phys. Rev. Lett., Vol. 122). Finally, the physical
and numerical models extending applicability of the equilibrium solution to the
case when intermittency region could also be in the non-equilibrium state is
introduced and verified in several test cases.
