Bicontinuous and cellular structure design of PVDF membranes by using binary solvents for the membrane distillation process

Abstract

With excellent permeability as the foremost requirement for membranes used in the membrane distillation (MD) process, the thermally induced phase separation (TIPS) method is a promising approach for preparing porous membranes with a bicontinuous structure, which is identified as the best morphology for permeation. The structure design of membranes prepared by the TIPS process can be strengthened when a binary solvent is introduced in the casting solution. In this work, the determination principles for binary solvent were explicated in detail, and further employed for the selection of binary solvent for the fabrication of polyvinylidene fluoride (PVDF) membrane with different structures. By the TIPS approach, the porous PVDF hollow fiber membranes with cellular structure were generated by g-butyrolactone (GBL)/dioctyl phthalate (DOP) and GBL/dioctyl adipate (DOA) binary solvents, while the membrane with a bicontinuous structure was produced from GBL/dioctyl sebacate (DOS) binary solvent. The phase diagram was used to explain a feasible mechanism for the formation of the porous structures above.When the morphologies and properties of the membranes were characterized and compared, the membrane with a bicontinuous structure rather than a cellular structure was identified as the potential structure for MD processes with much higher tensile strength, narrower pore size distribution, higher MD flux and excellent long-term performance.

On the Solubility and Stability of Polyvinylidene Fluoride

“…While blended solvent or diluent systems are sometimes used in PVDF processing to achieve specific effects such as a uniform membrane pore structure, these blends are typically composed of an effective solvent and an ineffective one [ 40 , 41 , 42 ]. In some cases, the ineffective solvent can make up as much as 95% of the blended system but nonetheless requires a small amount of effective solvent for dissolution to occur [ 43 ].…”

Robust Preparation and Pore Structure Design of Homogeneous Braid‐Reinforced PVDF Hollow Fiber Membrane

“…Generally, in order to obtain the mixed membrane structure with interconnected pores, many studies used TIPS or lowtemperature TIPS methods to prepare membrane through adjusting the competition of two different phase separation behavior. [35][36][37][38][39][40][41] But these studies all need a higher temperature, so we chose the NIPS method to prepare membrane through introducing DOP in casting solution. In the phase separation process, not only double diffusion of DMAc and water (liquid-liquid demixing) but also the placeholder and movement of DOP occurred.…”

“…And adjusting the composition of casting solution is a direct and effective means to control the phase separation process. Wang et al [35] prepared PVDF membranes with bicontinuous/ cellular structure by using good diluent (g-butyrolactone) and poor diluent (dioctyl sebacate/dioctyl adipate/dioctyl phthalate (DOP)) as mixed diluent based on the thermally induced phase separation (TIPS) method. Lu and Li [36] prepared a PVDF TIPS membrane with the mixed diluent of dibutyl phthalate (DBP, good diluent) and DOP (poor diluent).…”

A Review on Green Polymer Binder-based Electrodes and Electrolytes for All Solid-State Li-ion batteries

“…It acts as a great wall between the anode and cathode to avoid the blast. It plays a major role in the battery, where its properties can directly influence the activity of the batteries [46][47][48][49]. To enhance the performance of the solid-state battery, it should comply with the following properties (see Fig.…”