Development of membranes with well-dispersed polyampholytic copolymer via a composite coagulation process

Polyampholytes, particularly zwitterionic polymers, are commonly used for the surface modification of membranes. This helps to improve the antifouling properties, anti-adhesion properties, and biocompatibility of the membranes. Surface coating and grafting are common surface modification methods; however, these methods lead to pore blocking and stability problems because polyampholytes exist only on the membrane surface. We propose a strategy to fabricate membranes with well-dispersed polyampholytic copolymers via a composite coagulation process. Negatively charged membranes are fabricated in a coagulation bath containing a polyampholytic copolymer. Thus, both membrane preparation and modification via electrostatic adsorption can be achieved via a one-step process. Moreover, the polyampholytic copolymer is expected to be dispersed within the membrane matrix as well as on the membrane surface. The chemical compositions within the membrane were analyzed using X-ray photoelectron spectroscopy combined with argon beam etching technique. The results indicated that the polyampholytic copolymer was well dispersed within the membrane matrix fabricated via this composite coagulation process, whereas only a thin coating layer was formed on the membrane surface via the normal surface coating method. The newly fabricated membrane exhibited greater water flux, better antifouling properties, and higher stability than pristine and surface-coated membranes. This paper presents a method to prepare high-performance membranes with polyampholytic copolymers.