Capillary Flow Porometry
paper filter for capillary flow porometry

Capillary Flow Porometry

Capillary flow porometry (CFP) is a technique used to evaluate the through-pore size distribution and permeability characteristics of a variety of materials used as membranes and filtration media. These materials may include paper, synthetic polymers, textiles, ceramics, foams, hollow fibers, and more.

Through-pores are pores that start at one end of the sample surface and continue through to the opposite end. The largest through-pore size is referred to as the bubble point. For a material used as a separation barrier, the bubble point determines the largest particle size that could pass through the separation barrier. This parameter can be invaluable where rejection of particles above a certain size is required, or for the detection of potential defects in the barrier. Furthermore, the size distribution of the through-pores can help gauge what populations of particle sizes can be excluded, and can dictate flow characteristics or permeability through the filtration media. Permeability can be determined using air flow or a liquid of interest.

For a typical pore size analysis, a sample is wetted with a liquid to fill all through-pores and sealed into a sample holder. The wetting liquid is emptied from largest to smallest pores as increasing gas pressure is applied to one side of the sample. The resulting flow of gas is measured until all pores are emptied. This is referred to as the wet run. Analysis is then repeated on the dried sample without wetting. This is referred to as the dry run. The pore size distribution is subsequently calculated from the wet and dry curves according to the Washburn equation. Optimization of the analysis conditions could include pressure range applied, choice of wetting liquid, and sample size. In addition to thin sheet-like membranes, tubular structures such as hollow fibers could also be analyzed using this technique.

The instrument utilized at PTL can probe through-pores ranging in sizes from <0.02 to 500 µm. As such, this instrument uniquely complements PTL’s existing capabilities for characterizing open pores (any pores with an opening to the sample’s surface) by gas physisorption and mercury porosimetry techniques. The Porometer 3G is compliant with standards ASTM F316, ASTM F2450, and ASTM D6767 for capillary flow porometry as referenced by the instrument manufacturer.

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Advantages

  • Measurement of through-pores
  • Liquid or air permeability capabilities
  • Hollow fiber analysis is also available

Considerations

  • Does not measure closed-end/dead-end pores
  • Currently can accommodate samples up to 8 mm thick, but may be able to discuss other sample dimensions
  • Can measure a wide range of pore sizes overall, but results are optimal when focused on a more narrow pore size range

Sample Requirements

Our standard sample holder is for a 25 mm diameter sample and up to 4 mm thick. We have additional holders that can accommodate samples with diameters ranging from 10 to 50 mm in diameter and up to 8 mm thick. The instrument can actually accommodate many more sample configurations with available attachments.

For additional questions on your sample needs, please contact us to share specifics about your sample and options for suitable sample quantities.

Detection Range

This instrument can probe pores ranging in size from about 0.02 to 500 micrometers, though narrowing down the probed pore size range (e.g. by MIP) first is recommended for the best results.

Data Reported

In addition to the maximum, median, and minimum pore diameter size (µm), the Bubble Point data is also presented. If the thickness of the filter media is known, % porosity can also be estimated.

Instrumentation

Particle Technology Labs uses the Anton Paar/Quantatec Porometer 3G system to measure capillary flow porometry.

Anton Paar/Quantatec Porometer 3G zh

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