Computer Simulation Of Modified Polyvinylidene Fluoride Membranes

Membrane separation is a technique that allows specific components to pass through the membrane and intercepts the other impurities,it has been extensively applied in seawater desalination,wastewater treatment,biological medicine etc.While the driving force for filtration roots in the concentration difference between both sides of the membrane.During the filtration process,the separated impurities in the material can interact with the membrane,such as adsorption or deposition on the membrane surface or in the pore,resulting in smaller pore size or blockage of the membrane,which limits the further promotion of membrane separation technology.The research and preparation of anti-fouling membranes with good stability has become an important part for improving membrane separation technology.Polyvinylidene fluoride(PVDF),with hydrophobic,non-toxic and outstanding thermodynamic stability,has been widely used as a raw material for preparation of membranes.In the process of PVDF film synthesis,adding some modified materials to improve the performance of the film has been proved to be convenient and promising in the application.However,at the molecular level,the film formation process,the influence of modified materials on the film formation structure and its distribution on the film surface are still not fully understood.Through computer simulation,it is possible to explore related influencing factors more intuitively at the microscopic level,to predict experimental results and to provide guidance for the molecular design of functional materials.In this thesis,the dissipative particle dynamics(DPD)simulation method was used to study the influence of different modified materials on PVDF film formation.The influences of morphology change and different conditions on the pore size and surface material composition of PVDF film formation were also analyzed in depth.Firstly,the zwitterionic poly(carboxybetaine methacrylate)(PCBMA)was grafted to PVDF,it was added into the casting solution as a blend additive to simulate the process of non-solvent induced phase separation(NIPS).The effects of copolymer concentration,blend ratio and initial casting solution thickness on the membrane formation were investigated.Low blend ratio(10%)leads to low coverage rate of modification materials on membrane surface.Increasing the blend ratio to 15% can improve the surface coverage rate.The higher the proportion of PVDF-g-PCBMA/PVDF blends,the smaller the pore size.With the increase of the thickness of the initial casting solution,the interfacial mass transfer rate is accelerated due to the full interaction between the polymer and the solvent,which makes the film uniform.Then,we choose zwitterionic polymer brush poly(sulfobetaine methacrylate)-Tetraethyl orthosilicate(PSBMA-TEOS)grafted silicon dioxide nanoparticles(SNPs)and add them into PVDF polymer casting solution as a kind of additive.The formation process of zwitterionic polymer brush grafted SNPs blend membrane via NIPS method was discussed.The influence of PSBMA-TEOS structure on the anchorage of SNPs onto the membrane surface was studied by DPD simulations.With the increase of polymer concentration,the migration rate of SNPs to the surface becomes slower.When the concentration reaches 40%,some SNPs are embedded in the membrane.The length of PSBMA and the grafting ratio had certain effects on the membrane formation.When the grafting ratio of SNPs was 1,some SNPs were eluted into the solution.When the grafting ratio was 5,SNPs were uniformly dispersed and concentrated on the membrane surface.Finally,the formation process of zwitterionic nanogels was explored and used for PVDF membrane blending modification.Simulations could mimic and restore the microscopic process in experiments.A single factor approach was used to explore the influences of different concentrations and different polymer chain lengths on the formation of zwitterionic nanogels,as well as the morphology of PVDF modified membranes.