Computer simulation of the formation of anti-fouling polymeric ultrafiltration membranes with the addition of amphiphilic block copolymers

Abstract

The formation of an anti-fouling polymeric ultrafiltration membrane with the addition of amphiphilic block copolymers by immersion precipitation was simulated by applying a polymer bond fluctuation lattice model with the Monte Carlo method. First, the isothermal phase diagram of the quaternary system with the addition of block copolymers was calculated with the approximation method of ternary components. It was found that with the amount of amphiphilic block copolymer increasing the meta-stable section of phase diagram became wide and the unstable section became small. Our simulation showed that the amphiphilic copolymer with more and longer hydrophilic segments could increase the diffusion ability of nonsolvent in the process of membrane formation. The aggregation of amphiphilic block copolymers could induce the formation of closed pore structures. With the hydrophilic segment length of the amphiphilic block copolymer increasing, the closed pores coalesced to form the interconnected pore structures. By comparison, pentablock copolymers exhibited better performance in inducing the formation of porous structures than triblock or diblock copolymers because the pentablock polymers had more joining points which distributed at the phase interface and made the pore structures more stable. It was further found that M–N–M–N–M and M–N–M style copolymers (M and N were the hydrophilic and hydrophobic parts, respectively) as pore-formation agents were better than N–M–N–M–N and N–M–N style copolymers, respectively. These results were valuable to deeply understand and to tune the formation of the anti-fouling and high-flux polymeric ultrafiltration membranes using amphiphilic block copolymers.