Through-Thickness Micropore Polymer Membrane via Unidirectional Freezing
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Solution Overview
Problem
Current methods for preparing PTFE membranes are complex, inefficient, and difficult to scale commercially, as they do not form micropores through the thickness direction, leading to low permeability and potential solvent retention issues, especially in energy devices.
Innovation Solution
A method involving unidirectional freezing of a polymer solution followed by freeze-drying to create membranes with through-thickness micropores, allowing for controlled pore size and structure, reducing tortuosity and enhancing permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methods (solvent/non-solvent conversion or thermal phase separation) are used to prepare PTFE membranes, then the preparation process is complex and scaling is difficult, but the method does not form micropores through the thickness direction resulting in low permeability
Solution Approach 1:
The invention utilizes phase transition of the solvent (freezing and sublimation) to create through-thickness micropores. By unidirectionally freezing the polymer solution and then freeze-drying it, the solvent crystallizes and sublimates to leave interconnected pores extending through the membrane thickness, dramatically improving permeability compared to conventional methods
Solution Approach 2:
The invention transitions from forming pores in the plane direction to forming pores through the thickness direction by applying unidirectional freezing. This dimensional change in pore formation creates straight through-thickness channels rather than tortuous in-plane pores, enhancing permeability while simplifying the preparation process
2Productivity
If conventional solvent extraction method is used, then amorphous pores are formed increasing overall porosity, but the pores are not aligned in thickness direction and tortuosity increases
Solution Approach 1:
By utilizing the phase transition of solvent crystallization during unidirectional freezing, the invention creates aligned micropores through the thickness direction. The directional solidification process naturally forms pores that extend straight through the membrane, eliminating tortuosity while maintaining high porosity
Solution Approach 2:
The invention introduces asymmetry in the freezing process by applying temperature gradient unidirectionally through the membrane thickness. This asymmetric thermal field creates preferential crystal growth direction, resulting in aligned through-thickness pores rather than random amorphous pore structures
3Productivity
If high boiling point solvent is used in conventional method, then membrane preparation takes long time and solvent extraction is prolonged, but the solvent may remain in the membrane affecting energy device performance
Solution Approach 1:
The invention uses freeze-drying (sublimation) to remove the solvent instead of thermal extraction. The solvent transitions directly from solid ice to vapor, completely removing it from the membrane in a controlled manner. This eliminates solvent retention issues that would affect energy device performance while providing a clear endpoint for the process
Solution Approach 2:
The invention replaces the thermal extraction process with a mechanical phase transition process (freeze-drying). Instead of using heat to evaporate and extract the solvent over prolonged periods, the process uses controlled freezing followed by sublimation under reduced pressure, dramatically reducing preparation time and ensuring complete solvent removal
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method results in membranes with improved permeability and uniform pore size and wall thickness, minimizing fouling and enabling effective use in porous substrates, microfiltration, and energy device applications.
Implementation Method 1
unidirectional freezing in a thickness direction of a solvent
Implementation Method 2
forming micropores by extracting the solvent having a high volatility temperature that is soluble in water
Implementation Method 3
freeze-drying the resulting frozen material by the freezing
Data Source
AI summary
A polymer or polymer composite membrane having through-thickness micropores and a method of preparing the same are provided. More particularly, a polymer or polymer composite membrane having a pore structure such that micropores are aligned in a mesh structure in the thickness direction of the polymer or polymer composite membrane due to unidirectional freezing in the thickness direction of a solvent. The membrane has through-thickness micropores, and thus has improved permeability in the thickness direction and superior uniformity in size of the micropores and wall thickness between the micropores. For these reasons, the membrane can be used for a porous membrane substrate, microfiltration membrane, etc.