Preparation And Control Of High-performance Polymer Micro/Nano Porous Membrane

As a new type of functionalized material,porous polymer membrane has received extensive attention due to its important scientific value and application prospect in many fields such as photoelectricity,biomedical,high efficiency catalysis,separation and filtration,etc.At present,the“Breath Figure”method has attracted considerable in the preparation of porous membranes because of their advantages such as simple operation,low equipment,safe template and controllable pore size.However,the research how to efficiently and conveniently implement the preparation of thermoplastic polymers,especially thermosetting polymer micro/nano porous membrane is still inadequate.Therefore,based on the Breath Figure method,we fabricated a variety of advanced micro-structured thermoplastic porous membranes and high-performance thermoset polymer porous membranes by controlling process parameters to control the pore size,distribution and morphology of the porous membrane.The whole contents are listed as followed:1.Preparation and control of polystyrene（PS）honeycomb porous membranes.Based on Breath Figure method,we fabricated a various of PS porous membranes with different morphology by controlling the mass concentration of PS/tetrahydrofuran（THF）solution and the ambient humidity.The porous membrane was observed by scanning electron microscopy（SEM）,the pore size and porosity were measured,and the average diameter and statistical diameter distribution were calculated,and the conformational entropy of porous membrane was calculated by Voronoi Diagram.The effects of experimental conditions such as membrane concentration and ambient humidity（Relative humidity）on pore size and distribution were studied.The results indicated that the pore size of the porous membrane increases first and then decreases with the increase of the concentration of the membrane liquid,and increases with the increase of the ambient humidity.The PS porous membrane has a pore size distribution ranging from 1 to 5μm and a porosity of 40%to 60%.Porous membranes prepared at concentrations of 15 mg/mL and 90%RH had lower conformational entropy,ie higher ordering.2.Preparation and control of PLLA ordered porous membranes.Based on Breath Figure method,we fabricated a series of PLLA porous membranes with different morphology by controlling the mass concentration of PLLA/dichloromethane（CH₂Cl₂）solution and the ambient humidity.The porous membrane was observed by scanning electron microscopy（SEM）,the pore size and porosity were measured,and the average diameter and statistical diameter distribution were calculated.The effects of experimental conditions such as membrane concentration and ambient humidity on pore size and distribution were studied.The results indicated that the pore size of the porous membrane decreases with the increase of the concentration of the membrane liquid,and rose with the increase of the ambient humidity.The porosity increases first and then decreases with increasing solution concentration and ambient humidity.PLLA porous membrane has a pore size distribution ranging from 0.7 to 5μm and a porosity of 20%to 60%.3.Preparation and control of PLLA micro/nano fibers membrane.Based on Breath Figure method,we fabricated a various of PLLA micro/nano fibers membrane with different morphology by controlling the mass concentration of PLLA/THF solution and the ambient humidity.The porous membrane was observed by SEM,the pore size and porosity were measured,and the average diameter and statistical diameter distribution were calculated.The effects of experimental conditions such as membrane concentration and ambient humidity on pore size and distribution were studied.The results indicated that the PLLA micro/nano fibers membrane had a diameter range of 200¹000 nm,porosity>90%and surface-to-volume ratio range of 6⁸μm^-1 with a smooth and continuous three-dimensional network-like structure.The diameter rose while the concentration of the polymer solution increased,and decreased first and then increased with the increase of ambient humidity.The characteristic 3D nanofibrous architecture of PLLA membrane was formed by a combination thermal induced phase separation（TIPS）with water assisted breath figure mechanism,because of the sharp temperature drop caused by the quick solvent evaporation in the process.The optimal parameters to prepare micro/nano fibers membrane are 50μL（the dosage of PLLA solution）,300 mL/min（gas flow rate）,25 mg/mL（polymer concentration）,50%（environmental humidity）under 25℃dynamic atmosphere and THF as solvent.The micro/nano fibers had an average diameter of 476 nm.The porosity and surface-to-volume ratio of the membrane are up to 96.7%and 8.4μm^-1,respectively.4.Preparation and control of thermoset polymer ordered porous membranes.Based on Breath Figure method,we fabricated a various of benzoxazine（BOZ）/bismaleimide（BMI）porous membranes by controlling the mass concentration of BMI/BOZ solution and the ambient humidity.The curing characteristics of BMI/BOZ resin system was characterized by FT-IR,DSC,gel time test and viscosity test.The porous membrane was observed by SEM,the pore size and porosity were measured,and the average diameter and statistical diameter distribution were calculated.The effects of experimental conditions such as membrane concentration and ambient humidity on pore size and distribution were studied.The results show that the gel time of the BMI/BOZ resin system was shortened with the increase of BMI content and the peak temperature of typical curing exotherm was decreased with increasing BMI content.The pore size of the porous membrane decreases as the concentration of the membrane fluid increases,and increases with the increase of the ambient humidity.PLLA porous membrane has a pore size distribution ranging from 0.5 to 2.5μm and a porosity of 10%to 25%.The thermal stability and solvent resistance tests showed that the porous film remained in a porous structure after being immersed in an organic solvent for 24 hours or in a high temperature environment of300℃ for 2h.