Study On The Preparation And Salt Responsive Properties Of Smart Membrane With Ultrahigh Gating Ratio

Smart membrane,a separation membrane with stimulus responsive characteristics,can automatically adjust the physical and chemical properties of membrane surface and change the membrane pore size according to the changes of external stimulus signals,such as temperature,pH,light,electric field,magnetic field,the types or concentrations of ions/molecules and so on,so as to conveniently control the selectivity and permeability of the separation membrane remotely.So it has great application potentials in many fields,such as controlled transport,drug release,fine separation,tissue engineering and sensors and so on.Smart membrane is generally composed of two parts a common polymer membrane substrate and a stimulus responsive functional material,and its responsive capability is mainly determined by the nature or structure of the stimulus responsive functional materials.Stimulus responsive functional materials are mainly divided into three types:linear polymer chains,three-dimensional cross-linked network gels,and microgel spheres.At present,researchers often use only one stimulus responsive material to construct the smart membrane.As a result,due to the limited responsive capability of one stimulus responsive material,the responsive gating ratio(the ratio of the permeating flux of the smart membrane when stimulated to the permeating flux of the smart membrane when not stimulated)of smart membrane is usually low,which leads to its weak regulation ability for fluid transport and seriously limits its wide application.Therefore,it is very significant to develop smart membrane with high gating ratio.In this thesis,two kinds of stimulus responsive materials,linear polymer chains and nanohydrogels,were introduced onto the traditional polymer membrane substrate.Under the synergistic effect of two stimulus responsive materials,a salt responsive smart membrane with ultrahigh gating ratio was successfully prepared.The specific content is divided into the following two aspects(1)Zwitterionic nanohydrogels with amino groups were prepared by inverse phase microemulsion polymerization.And through adjusting the amount of emulsifier,the amount of water,the concentration of monomer and the addition of co-emulsifier,the inverse phase microemulsion polymerization system was gradually optimized,thereby increasing the production yield of zwitterionic nanohydrogels from 0.72%to 5.35%The average size of the prepared zwitterionic nanohydrogels is in the range of 55 nm to 65 nm.The salt responsive behavior of the zwitterionic nanohydrogels was tested.The experimental results show that the volume of the zwitterionic nanohydrogels remains basically unchanged in low concentration salt solutions,while the volume expands in high concentration salt solutions.(2)The zwitterionic nanohydrogels were grafted onto the poly(acrylic acid)chains on the surface and the pore wall of poly(acrylic acid)-grafting-poly(vinylidene fluoride)(PAA-g-PVDF)porous membrane through surface amidation reaction.As a result,a salt responsive smart membrane with ultrahigh gating ratio was successfully prepared Under the synergistic effect of the two functional materials,PAA chains and zwitterionic nanohydrogels tethered on PAA chains,the smart membrane exhibits an ultrasensitive salt responsiveness with a gating ratio of up to 89.6 times for Mg2+ions and 89.3 times for Ca2+ ions.In addition,the response of the smart membrane to the stimulus source is very rapid.In the process of continuous filtration,once the type or the concentration of salt solution is changed,the membrane permeating flux changes immediately.These characteristics show that the salt responsive smart separation membrane has an enormous application prospect in the controllable fluid transport.