About the Dominance of Mesopores in Physisorption in Amorphous Materials

Abstract

Amorphous, porous materials represent by far the largest proportion of natural and men-made materials. Their pore networks consists of a wide range of pore sizes, including meso- and macropores. Within such a pore network, material moisture plays a crucial role in almost all transport processes. In the hygroscopic range, the pores are partially saturated and liquid water is only located at the pore fringe due to physisorption. Therefore, material parameters such as porosity or median pore diameter are inadequate to predict material moisture and moisture transport. To quantify the spatial distribution of material moisture, Hillerborg’s adsorption theory is used to predict the water layer thickness for different pore geometries. This is done for all pore sizes, including those in the lower nanometre range. Based on this approach, it is shown that the material moisture is almost completely located in mesopores, although the pore network is highly dominated by macropores. Thus, mesopores are mainly responsible for the moisture storage capacity, while macropores determine the moisture transport capacity, of an amorphous material. Finally, an electrical analogical circuit is used as a model to predict the diffusion coefficient based on the pore-size distribution, including physisorption.

Comparison of the Calcium Carbide Method and Darr Drying to Quantify the Amount of Chemically Bound Water in Early Age Concrete

“…A significant part of it is hydrated, i.e., the liquid water is absorbed by the solid matrix and remains chemically bounded [ 14 ]. In addition, physisorption occurs, i.e., liquid water is adsorbed at the fringe of the emitting pore network [ 15 ]. Although this water interacts with the surface of the solid cement matrix, its binding energy is much lower compared to chemically bound water, even in the case of monolayer adsorption [ 16 ].…”

Micron-Sized Thiol-Functional Polysilsesquioxane Microspheres with Open and Interconnected Macropores: Effects of the System Composition on the Porous Structure and Particle Size of the Microspheres

“…Due to their advantages of large surface area, low density, and unique structure, porous materials have better performance than nonporous materials in many fields. Until now, researchers have always endeavored to obtain porous materials with tunable porous structures to improve their properties and meet different requirements, which depend on the desired speed of mass transfer or release of substances with target molecular sizes [ 9 , 10 , 11 , 12 ]. Macropores, with the pore size over 50 nm, can facilitate mass transfer and enhance interactions between the active sites on the surface and the substances outside the materials [ 13 ].…”