Investigation Of Surface Segregated Ultrafiltration Membrane And Related Anti-fouling Mechanism

Membrane fouling constitutes a bottleneck limiting the wide application of ultrafiltration technology; therefore, investigating the antifouling mechanism and developing methods to inhibit membrane fouling have become an important research issue in ultrafiltration area. In this dissertation, we have prepared different kinds of surface segregated membranes through segregation method, using poly(ether sulfone) as membrane bulk material, different amphiphilic polymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) as membrane surface modifying agent(MSMA), and protein solutions as model system. .DSC, XPS, FTIR, the static contact angle, and SEM were all introduced to characterize PES-Pluronic surface segregated ultrafiltration membranes. Due to the partial compatibility between PES and Pluronic, Pluronic segregated substantially during membrane formation, which increased the hydrophicity of membrane surface. And the SEM results indicated that the addition of Pluronic did not cause remarkable change on the asymmetry structure of membrane. In order to investigate segregation behavior of Pluronic during phase inversion in a wet processs, the surface coverage and residual ratio of Pluronic were calculated basing on XPS and FTIR results. It can be concluded that the molecular weight and the length ratio of hydrophilic segments to hydrophobic segments of Pluronic were two important factors influenceing Pluronic segregation behavior.Separation performance and anti-fouling properties of PES-Pluronic surface segregated ultrafiltration membranes were systematically investigated, and it was found that the addition of Pluronic enlarged the membrane pores, which decreased the protein rejection ratio; and the high density PEO segments appearring at membrane surface rendered the membrane with excellent protein-resistant ability and anti-fouling property. The protein adsorption amount on membrane surface decreased to as low as zero, and the flux recovery ratio could reach as high as 89%, which was much higher than that of PES control membrane, 62%.In order to increase the PEO density on membrane surface, a series of novel branched block polymers were prepared by simple substitution reaction based on Pluronic P123, and the effect of chemical structure of these MSMAs on the separation performance and anti-fouling ability of membranes was studied. The experimental results revealed that the block polymer with higher PEO arms number or PEO content exhibited stronger segregation ability, which rendered the membrane better anti-fouling ability.In order to investigate the effect of Pluronic on the phase behavior of membrane casting solution, the cloudy point line was plotted and coagulation value was measured, the results showed that the addition of Pluronic improved the stability of membrane casting solution. The molecular simulation calculation was conducted to preliminarily invesitgate the segregation performance of Pluronic during membrane formation and the phase behavior of membrane casting solution. The simulation results indicated that the difference of interaction between different components constituted the dominant reason for the different segregation performance of Pluronic; and the addition of Pluronic in casting solution resulted in larger reverse micelle, which might correspondingly lead to larger membrane pore appearing at membrane surface. Finally, the inherent relationship between the structural characteristics of block polymers and the anti-fouling ability of the membranes was studied; the guidance for the rational design and preparation of surface segregated ultrafiltration membrane was tentatively proposed.