Achieving superior Laplace pressure in electrospun PVDF/PAN Janus membranes: A morphological approach

Janus membranes have asymmetric wettability on each side. This contrasting structure gives them an internal driving force for spontaneous fluid transport (caused by Laplace pressure). The objective of this research is to attain the maximum Laplace pressure for electrospun PVDF/PAN Janus membranes by adjusting the fiber diameter and, consequently, the pore size and contact angle in each layer of the membrane. To achieve this goal, the Taguchi method was employed, and the parameters of the electrospinning process were modified to determine the optimal conditions for obtaining the smallest and largest fiber diameters for PAN and PVDF polymers. Accordingly, four distinct types of Janus membranes with different morphologies in each layer were synthesized. SEM analysis was employed to characterize the structural and morphological properties of the fibers in each layer. Additionally, the contact angle (CA) was measured to assess the hydrophilicity of each layer and determine the droplet penetration rate across the membrane. According to the results, the maximum Laplace pressure (205.60 kPa calculated by the analysis of SEM images and 197.4 kPa calculated by the bubble point test) and highest droplet penetration rate (0.83 µL/s) were attributed to the Janus membrane with the lowest pore size in the hydrophilic layer (0.65 µm) and the highest pore size in the hydrophobic layer (3.44 µm). The performance of the optimized membrane was evaluated with respect to unidirectional water transport and water–oil mixture separation. The results showed a rectification ratio of 3.92, a permeate flux of 7.9 × 104 L·m−2·h−1·bar−1, and a separation efficiency of 96.8 %. Finally, it was demonstrated that the Laplace pressure of the optimal Janus membrane in this study is 2.66 times superior to that of the best similar one in previous studies. The appropriate and allowable range for pore size and contact angle, necessary to attain a satisfactory Laplace pressure (exceeding 100 kPa), has been explored, determined, and recommended for future researchers to foster inspiration in the field of Janus membranes.