Determination of the porous channels size of filter materials

Abstract

Exploring advanced porous materials is of critical importance in the development of science and technology. Porous polymers, being famous for their all‐organic components, tailored pore structures, and adjustable chemical components, have attracted an increasing level of research interest in a large number of applications, including gas adsorption/storage, separation, catalysis, environmental remediation, energy, optoelectronics, and health. Pore structure use to describe the porosity, pore size, pore size distribution, and pore morphology of a porous medium. Maximum-sized pores play a significant role in the filtering process, since they determine the maximum sizes of particles of mechanical impurities that can pass through the filter material. Average pore diameters are used as a characteristic of porous materials when comparing them. To find the pore size distribution, the following methods are used: injecting mercury into the pores, displacing fluid from the pores, studying microphotographs, gas adsorption, X-ray scattering, etc. A common method of estimating the pore size distribution in filter materials is the mercury indentation method. Studies have been carried out on porous PTFE with various porosities. The materials were made by pretreating a mixture of dispersed pore-forming agent and polymer powder, followed by pressing at room temperature, heat treatment, leaching of the pore-forming agent and drying. Sodium chloride was used as a porogen. Leaching of the porogen was achieved by boiling in distilled water. Drying of the samples was carried out at t = 1000C for 12 hours. The volumetric porosity was regulated by the ratio of the amounts of the porogen and the polymer and varied in the range from 64 to 76%. The pore size was determined mainly by the dispersion of the porogen and the base material. A comparison of methods of obtaining data on the sizes of pore channels has been made. The most reliable values of the porous channels sizes are shown to be provided by the hydraulic method based on the joint solution of the Darcy and Hagen-Poiseuille equations. The maximum and average diameters of narrow sections of the pore channels, the tortuosity coefficients, and the permeability of porous polytetrafluoroethylene in the range of porosity values from 0.64 to 0.76 have been determined. It is established that an increase in the porosity of the material from 0.64 to 0.76 is accompanied by a decrease in the coefficient of tortuosity of the porouse channels from 2.4 to 1.3 and an increase in their permeability from 1.85 to 101.23D. With an increase in porosity, an increase in the ratio dmax and dav is also observed, which indicates an increase in the inhomogeneity of the pore structure.