Dissipative particle dynamics simulation on the polymer membrane formation by immersion precipitation

The kinetics of membrane formation by immersion precipitation is investigated using dissipative particle dynamics (DPD) simulation method. We study the influences of varying the chain length (N) of the polymer composing the membrane, the solvent size in the polymer solution, and the nonsolvent size and amount in the nonsolvent bath on the liquid-liquid demixing process and the membrane morphology in detail. The results are analyzed in terms of the characteristic domain size (R) in the polymeric membrane. R is as a function of simulation time, which first decreases, then increases due to the changes of the number of the interfaces between membrane polymer and nonsolvent. Moreover, the occurrence from spinodal decomposition to late stage domain coarsening is faster for the system with N = 40 than N = 100. When we take the chain-like instead of the one-site solvent, R turns to be larger at the same simulation time for the same system. But when we enlarge the nonsolvent size, it is surprising that the nonsolvent can not diffuse into the polymer solution to exchange for solvent. In addition, the domain size increases with increasing the amount of the nonsolvent, especially in the R coarsening process.