Difference between a Gas-Liquid Porometer and a Liquid-Liquid Porometer
The difference between a gas-liquid porometer and a liquid-liquid porometer lies in the nature of the fluids used and their interaction with the porous sample being analyzed.
A gas-liquid porometer is a device used to measure the pore size distribution and permeability of a porous material by measuring the flow of a gas through the sample. In this type of porometer, a wetting liquid inside the pores is displaced by a flow of liquid (usually gas), which allows us to establish the pore size and its distribution. By systematically increasing the pressure of the gas, the wetting liquid is pushed out from large to smaller pores, and these displacements are carefully recorded to calculate pore sizes. The gas-liquid porometer is particularly useful for characterizing larger pores and assessing the gas permeability of materials like membranes, filters, and porous ceramics. It provides information about the flow characteristics of gases through the material, helping to understand its transport properties. The pore size range for the Gas-Liquid Porometer is 0.013-500µm.
A liquid-liquid porometer, on the other hand, uses two immiscible liquids to analyze the pore structure of a porous sample. In this technique, the porous material is wetted with a liquid with a know surface tension and is placed in the equipment. This step is same as gas-liquid porometer but the difference is that in the liquid-liquid porometer the top of the sample is filled with a liquid that does not immerge with the liquid inside the pores. By systematically increasing the pressure applied to the liquid, the wetting liquid inside the pores are pushed out from large to smaller pores, and these displacements are carefully recorded to calculate pore sizes. This technique is particularly effective for analyzing smaller pore sizes and assessing the wetting properties of materials like membranes, hollow fibers, and thin films. The pore size range for the Liquid-Liquid Porometer is 0.002-0.2µm.
Comparison and Distinctions:
Despite the difference in using gas or liquid to push out the wetting liquid inside the sample’s pores, both gas-liquid porometer and liquid-liquid porometer uses the same equation to calculate the pore size (Washburn’s equation)
D = [4 γ cos θ] / P
Whereas,
D: Pore diameter, γ: Surface tension of wetting liquid, θ: Contact angle P: Gas/Liquid pressure
In the “surface tension” value mentioned in the calculation above, the interfacial surface tension between the wetting liquid and the gas to push out the liquid is used for the gas-liquid porometer and the interfacial surface tension between the two liquids for the liquid-liquid porometer. The fact is that if you can use a low value on this interfacial surface tension, you will be able to detect a smaller diameter pore using less liquid pressure applied to the sample. For instance, the Galwet wetting liquid has a gas-liquid surface tension of 15.9dyne/cm and this liquid has one of the highest wettability against samples (lowest surface tension). Although, if you use a certain combination of a liquid in the liquid-liquid porometer, the surface tension of the liquids can get as low as few dyne/cm. For instance, if you use a combination of a liquid which has a surface tension of 4dyne/cm, you can theoretically measure the same size pore using ¼ amount of pressure applied to the sample compared to using Galwet in gas-liquid porometer. This technique (liquid-liquid displacement) is especially effective if the sample you are testing is pressure sensitive, which means the pores of the sample might deform or break due to the high pressure of gas-liquid testing. Samples like hollow fibers and thin films are the best fit for the liquid-liquid porometers.
In summary, the key difference between gas-liquid porometry and liquid-liquid porometry lies in the fluids used to push out the wetting liquid from the sample’s pores. The choice between these techniques depends on the desired pore size range and the specific properties of the material under investigation. We offer a one-of-a-kind machine, the Ultra-Nano Porometer, which combines the gas-liquid porometry and liquid-liquid porometry in one single machine to be able to cover vast pore size range of 0.002-500 µm. This ultimate machine has capability of testing samples with small and fragile pores as well as samples with large pores which is difficult to measure using a liquid-liquid type porometer.