  We propose a continuum theory of the liquid-liquid phase separation in an
elastic network where phase-separated microscopic droplets rich in one fluid
component can form as an interplay of fluids mixing, droplet nucleation,
network deformation, thermodynamic fluctuation, \emph{etc}. We find that the
size of the phase separated droplets decreases with the shear modulus of the
elastic network in the form of $\sim[\mathrm{modulus}]^{-1/3}$ and the number
density of the droplet increases almost linearly with the shear modulus
$\sim[\mathrm{modulus}]$, which are verified by the experimental observations.
Phase diagrams in the space of (fluid constitution, mixture interaction,
network modulus) are provided, which can help to understand similar phase
separations in biological cells and also to guide fabrications of synthetic
cells with desired phase properties.
