Simple tools for complex phenomena: viscoelastic phase separation captured by disconnectable springs.

Viscoelastic phase separation is characterized by the formation of a transient gel upon phase separation. A transient gel state is widely observed in complex fluids including polymer solutions, colloidal suspensions, and protein solutions, but its physical description is quite difficult due to its intrinsically nonequilibrium nature. We have modeled this transient gel state using a type of Brownian dynamics simulation in which coarse-grained particles interacting with a Lennard-Jones potential are connected by elastic springs, which can be disconnected with the probability controlled by the ratio of the stored elastic energy to the thermal energy. The simulations well reproduce pattern evolution in a transient gel of a polymer solution. Our simulations indicate that domain morphology is controlled by two key physical factors: (i) the ratio between the nucleation and growth rates of domains of the less viscoelastic phase and (ii) the fragility of the transient gel.