Meaning
Measurement of pore throat geometry in porous media utilizes this technique to relate the pressure required to force a non-reacting gas through a liquid-saturated sample to the diameter of the largest pore restriction. Capillary flow porosimetry determines the pore size distribution and gas permeability of separators, membranes, and filters by increasing pressure incrementally until gas breaks through the liquid surface tension. This method relies on the Washburn equation to convert pressure data into specific pore diameters.
Analytical Procedure
Testing begins by wetting the sample with a fluid of known surface tension that occupies all available void spaces within the structure. Gradual gas pressure application creates a transition from liquid to gas phase transport across the smallest openings first and then the progressively larger ones until the sample sits completely dry. Automated sensors detect the flow rate at each discrete pressure step to generate a comprehensive distribution profile.
Physical Mechanism
Fluid movement inside porous matrices depends on the balance between external gas pressure and the capillary force acting at the liquid-pore interface. Smaller pores require higher pressure for gas penetration than larger openings due to the inverse relationship between diameter and pressure. Variations in pore connectivity and tortuosity influence the final data output by impacting the fluid resistance encountered during the displacement cycle.
Operational Significance
Selection of the appropriate wetting liquid determines the measurable pore size range and chemical compatibility with the test specimen. Accurate characterization of these void structures governs the liquid electrolyte retention capability and the ion transport efficiency of electrochemical cells. Proper assessment of pore dimensions allows manufacturers to predict the susceptibility of a separator to dendrite penetration or internal short circuits.
