Fabrication of Porous Polyimide Membrane with Through‐Hole via Multiple Solvent Displacement Method

Abstract

Porous polyimide (PI) membranes are widely used in separation processes because of their excellent thermal and mechanical properties. However, the applications of porous PI membranes are limited in the nanofiltration range. In this study, porous PI membranes with through-holes have been successfully fabricated by the novel multiple solvent displacement method. This new method requires only a porous polyamic acid (PAA) membrane, which was prepared by immersing PAA film in N-methylpyrrolidoneebk; (NMP) prior to immersing it in a mixed solvent consisting of NMP and a poor solvent, followed by immersion only in poor solvent. The pore size, morphology, porosity, and air permeability demonstrated that the fabricated PI membranes had a uniformly porous structure with throughholes over their surface. This new method enabled control of pore size (3-11 μm) by selecting a suitable poor solvent. This multiple solvent displacement method is highly versatile and promising for the fabrication of porous PI membranes.

Polymer Concentration and Liquid—Liquid Demixing Time Correlation with Porous Structure of Low Dielectric Polyimide in Diffusion-Driven Phase Separation

“…The PI sponge films prepared by precipitation for 120 min with 20 wt.% PAA concentration involve a sealed closed-cell surface layer ( Figure 4 ). This observation was consistent with the hypothesis that rapid phase inversion occurred on the outer surface when the PAA solution was directly immersed in a nonsolvent [ 23 ]. Therefore, PAA aggregation affecting the formation of a dense surface was detected.…”

Temperature-Invariant Large Broadband Polyimide Dielectrics with Multimodal Porous Networks

“…At a predetermined polymer concentration and liquid–liquid demixing time between the solvent and nonsolvent, the PPI- g -AMS films formed a sponge-like cross-section and a sealed closed-cell surface layer (Figure S2). This correlated with the hypothesis that a rapid phase inversion occurred at the outer surface when the PAA solution was directly immersed in the coagulation bath . This closed-cell structure helped in weakening WVP by restricting vapor to a cell-by-cell movement (Figures S3–S5).…”

“…This correlated with the hypothesis that a rapid phase inversion occurred at the outer surface when the PAA solution was directly immersed in the coagulation bath. 30 This closed-cell structure helped in weakening WVP by restricting vapor to a cell-by-cell movement (Figures S3−S5).…”

“…The Maxwell–Garnett model indicates that the porous structure in PI films can substantially reduce the dielectric permittivity since the D k of air ( k ≈ 1) is constant. , Porous PIs have been prepared using various methods, such as the use of blowing agents, the decomposition of a thermally labile domain in a phase-separated block or graft copolymer, and the inclusion of porous/hollow ceramic components − or porogens. − Although such methods require additives to create pores in the polymer matrix, thermodynamic phase separation allows the spontaneous formation of asymmetric porous structures in polymer matrix. Nonsolvent-induced phase separation (NIPS) is a method of fabricating a porous polymer film by immersing a homogeneous polymer solution in a poor solvent using the principle of phase separation. , At the beginning of the NIPS method, rapid phase separation can occur at the contact interface between the polymer solution and nonsolvent, resulting in a thin dense layer at the contact surface. , This layer can inhibit large water vapor permeation that deteriorates dielectric properties. An increase in porosity decreases the dielectric constant but tends to deteriorate the thermal and physical properties of the porous polymer. , Caution needs to be exercised regarding the morphological architecture and molecular network of PI to solve the difficulty in developing reliable ultralow-k dielectrics with multiple target properties.…”

“…28,29 At the beginning of the NIPS method, rapid phase separation can occur at the contact interface between the polymer solution and nonsolvent, resulting in a thin dense layer at the contact surface. 30,31 This layer can inhibit large water vapor permeation that deteriorates dielectric properties. An increase in porosity decreases the dielectric constant but tends to deteriorate the thermal and physical properties of the porous polymer.…”