Metastable lattice of droplets in phase separating polymer blends

Phase separation in a polymer mixture with an off-critical composition is described by a Ginzburg-Landau Hamiltonian that contains both cubic and quartic terms in the deviation of composition from its mean value in the homogeneous phase. Our analysis suggests that when a blend is brought in the vicinity of the spinodal, the initial homogeneous phase becomes unstable against the formation of a metastable lattice of spherical droplets whose lifetime diverges in the limit of infinite molecular weight. The composition of the droplets approaches that of the background phase and their size diverges with the approach to the critical point, but the composition contrast is enhanced and droplet radii become comparable to polymer dimensions, away from criticality. The connection between our predictions and the results of recent neutron scattering experiments is discussed, and new experiments that could probe the proposed droplet lattice are proposed.