Evapoporometry for Pore-Size Distribution in Membranes
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Solution Overview
Problem
Current methods for determining pore-size distribution in hollow fiber membranes are limited by the need for expensive equipment, high pressures that can deform the material, and the inability to accurately characterize small or irregular pores, particularly in ultrafiltration membranes.
Innovation Solution
The method involves using evapoporometry, which involves placing a porous material in a chamber with a volatile liquid, allowing evaporation to determine pore-related parameters based on mass loss over time, utilizing the Kelvin equation to relate vapor pressure depression to pore diameter, and requiring only multi-purpose laboratory equipment like a microbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If liquid displacement porometry is used to determine pore-size distribution, then continuous pores can be characterized, but high pressure causes compaction that alters the pore-size distribution and limits characterization to pores larger than approximately 10 nm
Solution Approach 1:
The patent uses gas adsorption and desorption phase transitions (condensation and evaporation) to characterize pores. The condensable gas condenses in pores at specific relative pressures according to the Kelvin equation, and evaporates during desorption, allowing pore-size distribution determination without applying high pressure that would deform the membrane structure.
Solution Approach 2:
The patent replaces the mechanical high-pressure liquid displacement system with a thermal field-based gas adsorption/desorption system. Instead of using high pressure to force liquid into pores, the method uses controlled gas adsorption driven by partial pressure gradients and temperature control, eliminating mechanical deformation of the porous material.
2Measurement precision
If mercury porosimetry is used to determine pore-size distribution, then both dead-end and continuous pores can be included, but very high pressures are required due to the high surface tension of mercury
Solution Approach 1:
The patent utilizes gas condensation and evaporation phase transitions to determine pore-size distribution. By controlling the partial pressure of condensable gas and monitoring condensation/desorption events, the method characterizes pores without requiring high pressure, unlike mercury porosimetry which must overcome mercury's high surface tension.
Solution Approach 2:
The patent changes the working parameters from high-pressure liquid/mercury systems to low-pressure gas systems with controlled partial pressures. By using gases with appropriate vapor pressures and controlling temperature, the method achieves pore characterization at much lower pressures than mercury porosimetry.
3Measurement precision
If gas adsorption/desorption is used to determine pore-size distribution, then both continuous and dead-end pores are included, but the determined PSD must be corrected for the t-layer
Solution Approach 1:
The patent employs feedback mechanisms where the adsorption and desorption data are used to iteratively determine and correct for the t-layer thickness. The method uses the hysteresis loop characteristics and adsorption/desorption isotherm data to calculate and apply corrections for the adsorbed layer, improving the accuracy of pore-size distribution determination.
4Measurement precision
If permporometry is used to determine pore-size distribution, then only continuous pores are determined, but it requires control and measurement of non-condensable carrier gas and condensable gas flow rates and partial pressures across the membrane as well as temperature
Solution Approach 1:
The patent extracts and eliminates the complex multi-parameter control requirements of permporometry by using a simplified gas adsorption/desorption method. The approach removes the need for simultaneous control of carrier gas flow, condensable gas flow, partial pressures, and temperature, focusing instead on controlled gas adsorption at defined relative pressures.
5Measurement precision
If direct observation methods such as SEM are used to determine pore-size distribution, then the pore structure can be directly imaged, but high vacuum and drying are required which can alter the pore structure
Solution Approach 1:
The patent replaces direct mechanical/optical observation methods (SEM, AFM) with an indirect thermodynamic method based on gas adsorption/desorption equilibrium. This substitution avoids the need for vacuum drying and conductive coating, preventing alteration of the native pore structure while still providing accurate pore-size distribution data through thermodynamic measurements.
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
Evapoporometry provides a cost-effective and accurate characterization of pore-size distribution across a wide range of pore sizes, from nanometers to microns, without deforming the material, and can assess internal pore fouling, offering advantages over traditional methods by characterizing larger membrane areas with higher accuracy and sensitivity.
Implementation Method 1
allowing evaporation to determine pore-related parameters based on mass loss over time
Implementation Method 2
utilizing the Kelvin equation to relate vapor pressure depression to pore diameter
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
According to embodiments of the present invention, a method for determining at least one pore-related parameter of a porous material is provided. The method includes supplying a volatile liquid into a chamber, placing a porous material within the chamber, spaced apart from and over the volatile liquid, determining an effective mass of the chamber over a period of time, and determining at least one pore-related parameter of the porous material based on the effective mass determined. According to further embodiments of the present invention, an arrangement for determining at least one pore-related parameter of a porous material is also provided.