Porous Membrane Cross-Sectional Pore Size Gradient
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Solution Overview
Problem
Existing porous membranes for water filtration struggle to balance high blocking performance with high water permeability, particularly in clarifying river water for tap water, as they often have small cross-sectional pore size gradients that limit water permeability.
Innovation Solution
A porous membrane with a cross-sectional pore size index of 40 or more in specific regions, formed from a vinylidene fluoride-based resin, featuring a three-dimensional network structure and varying pore sizes to enhance water permeability while maintaining blocking performance, with a compression resistive strength of 0.40 MPa or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cross-sectional pore size is reduced to improve blocking performance, then virus and germ removal is enhanced, but water permeability decreases
Solution Approach 1:
The membrane employs a non-uniform pore size distribution where the cross-sectional pore size varies through the membrane thickness. The pore size is smaller near the feed water side (0-0.1 normalized thickness) for effective blocking, and progressively larger toward the permeate side (0.6-1.0 normalized thickness) to facilitate water permeation. This local variation in pore quality resolves the contradiction between blocking performance and water permeability.
Solution Approach 2:
The invention transitions from considering only the surface pore size to incorporating the pore size gradient through the membrane thickness dimension. By defining cross-sectional pore size at different normalized thickness positions (0-1) and establishing specific index requirements (e.g., index ≥40 at position 0.1-0.2, index ≥70 at position 0.2-0.3), the solution adds the thickness dimension to optimize both blocking and permeability simultaneously.
2Strength
If the membrane thickness is increased to improve strength for long time use, then mechanical strength is enhanced, but water permeability decreases
Solution Approach 1:
The membrane structure employs local quality variation by creating different pore size characteristics at different thickness positions. The region near the feed water side (0-0.3 normalized thickness) has smaller cross-sectional pore sizes for blocking, while the region near the permeate side (0.6-1.0 normalized thickness) has larger cross-sectional pore sizes for permeation. This allows the membrane to maintain adequate strength while optimizing water permeability through the thickness gradient.
Solution Approach 2:
The membrane uses a composite pore structure combining regions of different pore sizes within a single layer. This composite architecture integrates the blocking function (small pores) and permeation function (large pores) in different spatial zones, achieving both mechanical strength and high water permeability without requiring multiple separate membrane layers.
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 membrane achieves high blocking performance and excellent water permeability, ensuring stable filtration over a long period with improved chemical resistance and resistance to fouling substances.
Implementation Method 1
A porous membrane having a cross-sectional pore size index of 40 or more in a region where the membrane thickness position ranges from 0.1 to 0.2 within the membrane thickness which is normalized by defining one surface position as 0 and the other surface position as 1 and divided into ten regions in the membrane thickness direction
Data Source
AI summary
Provided is a porous membrane having a high blocking performance suited for filtration application as well as being excellent in water permeability performance, which is capable of providing stable filtering operation over a long period of time. The porous membrane has a cross-sectional pore size index of 40 or more in a region where a membrane thickness position ranges from 0.1 to 0.2 within the membrane thickness which is normalized by defining one surface position as 0 and the other surface position as 1 and divided into ten regions in the membrane thickness direction, the cross-sectional pore size index being calculated by: Cross-Sectional Pore Size Index=(Cross-Sectional Pore Size in the Range)/(Pore Size of the One Surface).