What is micropore filling? What is capillary condensation? -Huaqiang Electronic Network

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Microporous filling: Due to the enhancement of the adsorption potential, there is obvious adsorption enhancement in the micropores, and the adsorption molecules at low relative pressure have a relatively strong capturing ability. This mechanism of promoting adsorption at a very low relative pressure due to the overlap of the adsorption potentials of the opposite pore walls in the micropores is called microporous filling.
Capillary agglomeration: In a porous adsorbent, if a concave liquid surface can be formed at the initial stage of adsorption, according to the Kelvin formula, the vapor pressure on the concave surface is always smaller than the saturated vapor pressure on the flat surface, so when it is less than the saturated vapor pressure, The surface of the concave liquid has reached saturation and the condensation of steam occurs. The effect of this steam condensation always moves from the small hole to the large hole. As the gas pressure increases, the capillary pores where the gas condenses become larger and larger; At the same time, since the radius of curvature of the liquid surface after capillary aggregation is always smaller than that before capillary condensation, the desorption pressure is always smaller than the adsorption pressure at the same adsorption amount.
Micropore filling is similar to capillary condensation in that the pores are filled, but are essentially different. Microporous filling is a microscopic phenomenon that depends on the enhanced potential energy between the adsorbed molecules and the surface, occurs in the micropores, and the relative pressure is very low; while capillary condensation is a macroscopic phenomenon depending on the characteristics of the meniscus of the adsorbed liquid. The necessary condition for capillary condensation is that the pores can accommodate at least the next two layers of particles, occurring in the mesopores, and under intermediate relative pressure. Nitrogen is the adsorbate and generally has a radius of about 1.6 nm.