Molecular Simulation Method Of The Effects Of Additives On The Structure And Properties Of Polyethersulfone (PED) Membranes

PES（polyether sulfone）is widely used as polymer membrane materials due to its excellent mechanical properties and good chemical stability.Additives are usually used to regulate pore structure and properties in membrane preparation.However,at present,the effect of additives on film properties remains at the level of experimental research,and there is still a lack of understanding of the interaction mechanism between additives and film materials,as well as the effect mechanism of additives on film structure and properties.In this study,PES membrane models including various additives were created using a combination of molecular dynamics simulation and mesoscopic simulation.The effects of additives on the microstructure and characteristics of PES membranes were investigated at the molecular and mesoscopic levels.This work has a good reference significance for revealing the action mechanism of additives and guiding the development and design of membrane materials from the molecular level.The main contents are as follows:（1）The effects of several typical additives on membrane structure and properties were studied.Polyethylene pyrrolidine（PVP）,and lithium chloride（Li Cl）and polyethylene glycol（PEG）was added to the PES membrane model to explore the effect of the type of additive on pore shape and size,membrane structure stability,the pure water flux and the anti-fouling properties of the PES membrane.After the modification of PES membrane with PEG additive,the membrane pore became larger,the water diffusion coefficient increased,and the PES membrane structure became more stable.（2）The effects of molecular weight（200 Da,400 Da,600 Da）and content（4%,12%,24%）of PEG on PES membranes were studied.The interaction between PES molecules,the movement of PES molecular chains,the free volume in PES membranes,the diffusion coefficient of water molecules,and the adsorption of humic acid（HA）on PES membranes were analyzed.After the addition of PEG,the molecular motility of PES was weakened and the stability of PES membrane was improved.When the PEG content increased from 4%to 24%,the free volume in the membrane increased from48%to 75%.When the addition amount of PEG was 4%,the free volume of membrane with different molecular weight PEG were all 48%.With the addition of 4%PEG 200,the diffusion coefficient of water molecules in the membrane increased to0.57×10^-6 cm²·s^-1,and the pure water flux of the membrane also increased by 2times.This indicates that PEG can increase the pure water flux of the membrane,but compared with the content,PEG molecular weight has less effect on the membrane pore and water flux.In addition,the analysis of adsorption energy and interaction energy of HA on the membrane proved that the hydrogen bond between HA and PEG enhanced adsorption,but this effect would be weakened with the increase of the addition amount,the adsorption site of HA on the membrane would also be reduced because of the curve of PES.In other word,PEG is not beneficial to the anti-fouling performance of PES membrane.（3）Dissipative particle dynamics（DPD）was employed to explore the effect of PEG on PES membrane structure on a larger scale.The mesoscopic model of PES membrane with different PEG molecular weight and addition amount was established,The cluster radius of PEG 200,PEG 400,and PEG 600 were all close to 33（?）when the PEG content was 4%.When the concentration reached 12%,the radius of all clusters grew to 40（?）.When the concentration increased to 24%,the radius of all clusters approached 46（?）.It proves more directly that the amount has significant effect on pore size and structure of PES membrane comparing to the molecular weight of PEG.