The morphology and dynamics of viscoelastic phase separation in polymer solutions are investigated by the use of a graphic process unit (GPU) accelerated three-dimensional numerical simulation of a viscoelastic model for the first time.The results show the bulk stress is a prerequisite to the phase inversion.In agreement with the phase inversion observed in previous experiments

the polymer rich domain first forms a continuous network structure and then shrinks and inverts to a dispersed droplet structure.Interestingly

the growth of the bulk relaxation modulus suppresses the concentration fluctuation in the early stage of phase separation

and the phase inversion is thus delayed by the increase of bulk relaxation modulus.On the other hand

the growth of the bulk relaxation modulus increases the domain growth rate in the late stage of phase separation and leads to larger-sized polymer rich domains.Additionally

the growth of the shear relaxation modulus can help polymer rich domains to maintain network-like structures

and in the case of a larger shear relaxation modulus

the shear stress can exist for a longer time due to the slow relaxation of irregular polymer-rich domains in the late stage of phase separation.