Rigid Polymers Enhance the Mechanical Resilience of High-Flux Poly(vinylidene fluoride) (PVDF) Antifouling Membranes

Hydrophilic modification is widely used to improve the permeability and antifouling properties of PVDF membranes. However, introducing flexible hydrophilic segments significantly reduces the membrane’s resistance to deformation. To address this contradiction, a mature amphiphilic copolymer─fluoride-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA)─was used as the hydrophilic component, while a multiarm rigid polystyrene (referred to as Star-PS) was introduced as a structural regulator. With the increase in Star-PS content, the average pore size and porosity first increased and then decreased. At the optimal Star-PS content of 0.5 g, M₂ exhibited the largest average pore size of 67.4 nm and the highest porosity of 75.1%; while when the content increased to 0.8 g, these values decreased to 59.8 nm and 71.3%, respectively. During the nonsolvent-induced phase separation process, Star-PS undergoes local aggregation and microphase separation, forming microspheres rich in polystyrene (PS), with an apparent equivalent diameter of approximately 250–350 nm. These retained rigid microregions can regulate the evolution process of the polymer-rich and polymer-poor phases, promote the growth and connection of finger-like channels, and limit the deformation of the surrounding polymer matrix. However, excessive Star-PS will increase the viscosity of the casting solution and delay phase separation, thereby partially inhibiting pore formation. Therefore, M₂ achieved a pure water flux of 556.4 L/(m²·h), a sodium alginate (SA) retention rate of 86.72%, and a flux recovery rate of 77.4%. Compared with M₀, its hardness, elastic modulus, and storage modulus increased from 1.6, 25.34, and 24.84 MPa to 9.5, 125.82, and 35.9 MPa, respectively. Thus, the contribution of this study lies in the use of the in situ formed rigid microregions of Star-PS to compensate for the mechanical performance degradation caused by hydrophilic modification, while maintaining good permeability and antifouling properties.