چكيده لاتين
Janus membranes have garnered significant attention due to their ability to facilitate unidirectional fluid transport and their extensive applications in aqueous-organic phase separation. In this study, a PVDF/PAN Janus membrane was fabricated using electrospinning, and its performance was optimized in terms of Laplace pressure, hydrophilicity, porosity, and mechanical properties. Initially, four types of Janus membranes with different morphologies—JInOn, JInOm, JImOn, and JImOm—were designed and evaluated. The minimum and maximum fiber diameters for PAN and PVDF polymers were measured at (172 ± 38 nm, 991 ± 99 nm) and (139 ± 44 nm, 1002 ± 80 nm), respectively. Contact angle analysis revealed that the JInOm membrane, with the smallest fiber diameter in the hydrophilic layer and the largest in the hydrophobic layer, exhibited the best performance, achieving a total Laplace pressure of 205.60 kPa and a droplet penetration rate of 0.83 µL/s. This performance was attributed to the stronger wicking effect in the hydrophilic layer and the reduced hydrophobicity of the hydrophobic layer. In the second phase of the study, porosity within the PAN fiber layer was enhanced using selective removal (SR) and non-solvent-induced phase separation (NIPS) methods. In the SR method, sacrificial components such as PVP, PEG, NaHCO₃, and Na₂SO₄ were employed to create significant intrafiber porosity. Among these, NaHCO₃ produced the highest porosity (86%) due to CO₂ gas generation during its reaction with HCl. The internal pressure caused by CO₂ generation was the primary factor driving this increase in porosity. Comparatively, PEG outperformed PVP as a sacrificial component because residual PVP within the fiber matrix, confirmed through ATR-FTIR analysis, hindered porosity formation. The NIPS method, combined with vapor-induced phase separation (VIPS), also proved effective. Using a 5% non-solvent concentration provided optimal conditions for increasing porosity while maintaining mechanical properties. These methods improved hydrophilicity and simplified and stabilized the electrospinning process. The third phase of the study focused on enhancing the hydrophilicity of the PAN layer. Alkaline hydrolysis, a simple and cost-effective method, was selected for this purpose. By converting nitrile groups into amide and carboxylic acid groups, surface hydrophilicity was increased. Analysis showed that a hydrolysis time of 18 minutes resulted in optimal conditions, reducing the contact angle to 32° and improving water absorption. Prolonged hydrolysis times, however, negatively affected mechanical properties. The final membrane demonstrated a separation efficiency of 99.4 % and a permeate flux of 12.2×104 L.m-2.h-1.bar-1 in water-oil mixture separation tests. By employing combined and innovative modification approaches, this study successfully optimized the Laplace pressure, porosity, and hydrophilicity of the Janus membrane. The findings open new horizons for the design of advanced membranes tailored for industrial and environmental applications.
