What Is a Capillary Flow Porometry (CFP)?
Capillary flow porometry is optimal for analyzing pores that directly contribute to fluid transport (open, permeable, or through-pores). It has a wide dynamic range of measurable pore sizes and the unique ability to determine through-pore gas permeability and bubble point. Measurements of larger pores are much faster than acquiring gas adsorption isotherms (~30 minutes versus 8-24 hours), which is necessary for nanoscale porous materials.
Other details:
- Must be a solid material with gas-permeable through-pores.
- Must be completely wettable by a liquid suitable for analysis.
- Pore size range between ~ 0.02 to 500 µm.
- Must be sealable using an O-ring – not too rough and rigid.
Wide Measurement Range
Rapid Measurements
Non-Destructive
Why Use CFP?
- Pore size and gas permeability determination of through-pores in permeable materials.
- Determine the pore size distribution in the size range of: ~0.02 to 500 µm.
- Bubble point, cumulative flow percent, and pore density determination.
Measure the Pores That Matter
Fast, Non-Destructive Testing
Full Performance Insight
How CFP Works
A porometry measurement involves first thoroughly wetting the sample with an appropriate wetting solution. This fluid fills the pores and blocks gas from flowing through them via capillary forces that are described by the Washburn equation:
D=(4γ∙cosθ)/ΔP
where D is the pore/capillary diameter, is the known surface tension of the wetting liquid, θ is the contact angle between the liquid and pore surface / capillary wall (should be 0° if fully wetted), and ΔP is the differential gas pressure applied by the porometer.
The sample is sealed between a mesh support screen and an O-ring. Gas pressure is then directionally applied and ramped up. As the gas pressure increases, the wetting fluid is evacuated from more and more pores, with larger pores emptying first due to the lower capillary forces holding the wetting fluid inside. A dry run without the wetting fluid is also performed to determine which phase in the wet run aligns with when the pores have fully evacuated.
Equipment Used for Nanoindentation
Anton Paar Porometer 3G zh
- Minimum Detectable Pore Size: 13 nm.
- Maximum Detectable Pore Size: 500 μm.
- Flow Rate Range: 0.01 to 200 L/min.
- Flow Sensor Temperature Coefficient: < 0.5% / °C
(from 15 to 45 °C). - Maximum Pressure: up to 500 psi (34.5 bar).
- Pressure Accuracy: ± 0.05% f.s.
Key Differentiators
Strengths
- Rapid and reproducible measurements are ideal for applications like filtration media.
- Generally non-destructive and non-toxic analysis conditions.
- Wide dynamic range of measurable pore sizes.
- Only measures open, permeable pores which are relevant to fluid transport.
Limitations
- Not suitable for nanoporous materials (< 20 nm).
- Pore density must not be excessively restrictive to flow.
- Pores must be open and through-connected, i.e., permeable with gas flow.
Example Outputs
Sample Requirements
The sample must be a solid material with gas-permeable through-pores. The standard size is 25 mm with a maximum thickness of 3 mm (other configurations may be possible). The sample must be completely wettable by a liquid suitable for analysis. A pore size range between ~0.02 – 500 µm is generally accepted. The sample must be sealable using an O-ring; not too rough and rigid, but able to withstand 100+ psi of gas pressure during analysis.
CFP Applications by Industry
Battery Separators
Must be permeable to ions to allow charge to move, while providing a non-conductive barrier that stops direct contact between the anode and cathode. Porometry can probe this permeability, though pore size limitations may come into effect in some configurations.
Filtration Media & Membranes
Capillary flow porometry is ideal for analyzing the proper construction and performance of filters and membranes. This includes pore maximum, minimum, and average sizes, pore-size homogeneity, and gas permeability. These filters allow materials of specific sizes to flow efficiently while catching or removing all larger debris.
Textiles
Porometry can be an important technique to test the breathability of textiles by characterizing the pore sizes and gas permeability. This is important for the comfort and safety of the wearer, as heat and air must pass primarily one-way through the material while preventing precipitation, debris, or other material from passing into or through the material.
Techniques That Complement Capillary Flow Porometry
Why Choose Covalent for Your Capillary Flow Porometry Needs?
We offer several complementary techniques for completely characterizing the pores in our clients’ materials of interest and other physical and chemical properties related to the material performance. At Covalent, we can prepare samples in-house to make them measurable and ultimately deliver the valuable data you need.