Capillary flow porometers employ the technique of expelling a wetting liquid from through-pores in the sample. Gas pressure is automatically applied to one side of the sample and as pores empty the resulting gas flow through the open pores is accurately measured by the on-board microprocessor. The actual pressure at the sample is measured independently of the pressure control circuit to ensure the highest quality data.
Capillary flow porometers can also measure permeability. Without modification they can acquire gas permeability data at a single desired pressure, with stabilization defined by pressure or flow, and across a range of pressures at chosen stabilization times. Liquid permeabilities can also be determined using an optional accessory.
Pressure is just one aspect of porometry. The other is flow rate. As the pressure is increased to empty smaller and smaller pores of the wetting fluid, gas flow continues through previously opened pores, and must be continuously and accurately measured. A small number of pores results in a low flow, a larger number of pores results in a larger flow. The same number of large pores as small pores also results in a higher flow rate
While in theory any wetting liquid could be used, in practice useful porometry work requires a liquid with predictable performance and desirable physical properties. Porofil, a fluorocarbon, is such a liquid. It has a very low surface tension (just 16 dynes/cm), will even wet polytetrafluoroethylene (PTFE), is chemically inert, and will not swell materials like water and alcohol can.
Read more about pore size distribution and analysis.
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