Study On Preparation And Performance Of Thermo-and PH-Responsive Smart Gating Membranes

Environmental stimuli-responsive smart membranes show potential applications in many fields,for instance,controlled release,intelligent control separation,sensors and chiral separation.So far,there are very few reports on the research of smart gating membranes with both temperature and pH response.The research on the smart gating membrane for constructing microgel-like water gates on pore surface by in-situ self-assembly technology has not been reported.Therefore,it is of great significance to study the preparation method,structure-activity relationship and stimuli-resposive mechanism of these smart gating membranes,and to further construct thermo-and pH-responsive membranes with excellent gating ratios and reversible response performance.In this work,several kinds of thermo-and pH-responsive smart gating membranes were successfully designed and fabricated by constructing water gates on the pore surface of polymeric porous membranes and the layer spacing of graphene oxide sheets.A two-step free radical polymerization method was used to prepare dual responsive P4VP core/PNIPAM shell microgels.Then,the thermo-and pH-responsive smart gating membranes were prepared by phase-inversion method using polyvinylidene fluoride?PVDF?as the membrane material.The stimuli-responsive microgels underwent in-situ surface segregation and uniformly decorated on the surface of internal channels during the phase-inversion process.The hydraulic permeability performance of smart gating membranes has been studied within 20⁵0°C and a wide pH range?spanning pH 2⁶?.The results show that these prepared membranes have positive thermo-responsive behaviors and positive pH-responsive characteristics.Moreover,these prepared smart gating membranes have excellent dual response performance.The water flux of optimized membrane?M2?varied from 1.94 kg m^-2 h^-1 at 20?°C/pH 2 to 474.91 kg m^-2h^-1 at 50?°C/pH 6,with a high gating ratio of 245.Investigations revealed that microgels based on different thickness of PNIPAM shell conferred different thermo-/pH-responsive properties to the SGMs.For example,the thicker PNIPAM shell enhanced the thermo-responsive property,while the pH-responsive performance was restrained.A series of single or dual thermo-/pH-responsive smart gating membranes were prepared by in-situ assembled stimuli-responsive microgels as water gates.The highly cross-linked poly?N-isopropylacrylaminde-co-methylacrylic acid?P?NIPAM-MAA?microgels underwent in-situ surface segregation during the acetic acid-assisted phase-inversion process,and they were uniformly decorated on membrane surface and inner channels surface.The hydraulic permeability performance of SGMs was studied within a temperature range of 25⁷0°C and series of wide pH gradients?spanning 3¹1pH units?.Incredibly high stimuli-responsive gating coefficient of about 134.6 could be obtained from the dual responsive membrane M0.2.Investigations revealed that microgels based on different NIPAM/MAA ratios conferred different thermo/pH-responsive properties to SGMs.Higher NIPAM/MAA ratios determined the thermo-responsive performance,and higher MAA/NIPAM ratios dominated the pH-responsive performance.Moreover,the SGMs with in-situ assembled microgels on surface and channels surface have enhanced gating coefficients,stimuli-reversible behaviour and self-cleaning performanceBased on the nanochannels in the graphene oxide?GO?membrane,we designed positive thermo-and negative pH-responsive GO/hydrogel composite membranes?GOGMs?through a simple filtration-assembly technology.In the self-assembly of GO and hydrogel,the shape-flabby hydrogels can be perfectly inlaid between two GO sheets by changing their shape,and the hydrogels also act as a bond between GO and substrates.Thermo-and pH-responsive hydrogels embedded between the GO sheets impart adjustable water channels to the GO membranes.The channel tunability of hydrogel-studded GO membrane is controlled by the size conversion of hydrogels and the constant layer spacing of GO sheets.The results revealed that membrane thickness and the ratio of microgel to GO both have effects on the water permeation and response performance of GOGMs.The prepared smart gating membrane has high thermo-and pH-responsive gating coefficient,reversible response performance and intelligent penetration of small molecules.In summary,this study successfully designed and prepared several thermo-and pH-responsive smart gating membranes by using phase-inversion method and assembly technology.The prepared smart gating membranes were studied through structural analysis,thermo-and pH-responsive flux experiments,reversible response experiments,self-cleaning experiments and stimuli-responsive permeation/interception experiments.The results showed that these smart gating membranes have excellent thermo-and pH-responsive behaviors,reversible response,self-cleaning properties and intelligent separation performance.