Hydraulic Permeability Of Electrospun Fibrous Membranes

The electrospun fibrous membrane has been widely studied and achieved applications in many fields due to its high porosity,large specific surface area and excellent mechanical properties.At present,there are few studies on the permeability characteristics of non-woven and quasi-parallel fibrous membranes inland.The permeability of electrospun polyacrylonitrile(PAN)fibrous membranes and the liquid entry presssure of poly(vinylidene fluoride)(PVDF)fibrous membranes have been studied in this work on a custom-built hydraulic penetration device.The parameters of fibrous membranes and fluids have been taken into consideration.The non-woven and quasi-parallel fibrous membranes of different concentrations of PAN and PVDF solutions were prepared by controlling parameters of electrospinning process.The parameters of membranes such as surface morphology,diameters,porosity etc.were characterized.The results indicate that the pores of fibrous membranes are interpenetrating,the surface of the fibers are smooth,the diameter of fibers are at sub-micron level,and the minimum diameter of fibers can reach to 200 nm.The porosity of PAN and PVDF fibrous membranes are 80% ~ 95% and 70% ~ 85%,respectively.The fibers with smaller diameter have the higher porosit,and the porosity of the quasi-parallel fibrous membrane is smaller than that of the nonwoven membrane with the same diameter due to its fiber alignment.Secondly,nonwoven and quasi-parallel PAN and PVDF fibrous membrane with three fiber diameters were selected for hydraulic penetration experiments.The influence of different membrane parameters as well as the flow velocity of deionized water on the permeability of the fibrous membrane were investigated.The results indicate that water will drag fibers when it flows into pores of the PAN fibrous membrane and then the slippage,bending and adhesion will happen in the fibers.The PAN fibrous membrane is compressed,resulting in the decline of porosity and permeability.However,PVDF fibrous membrane needs pressure to let water flow into its pores due to the hydrophobicity.When the pressure reaches a certain value,the water can permeate into pores of the PVDF fibrous membranes.And this pressure is named LEP(Liquid Entry Pressure).LEP is related to the pore diameter of the PVDF fibrous membrane,the diameter of the fibers and the surface tension of fluid.Finally,the influences of dynamic viscosity and surface tension on the permeability of the fibrous membrane were investigated by controlling the temperature of deionized water,the mass concentrations of NaCl solutions and ethanol solutions.The results indicate that the permeability of PAN fibrous membrane increased as the fluid dynamic viscosity increased.And the experimental results were consistent with the theoretical formulas.For deionized water,its dynamic viscosity will decline as temperature increases so that the permeability of the membrane will reduce.But as internal energy and molecular kinetic energy of water increases,the diffusion velocity of water molecules increases that will cause the improvement of the permeability.According to the result of the experiment,permeability is not related to temperature.With the surface tension of the fluid increasing,the LEP of the PVDF fibrous membrane increased,and the experimental results were consistent with the theoretical formulas.