Changes in water vapor adsorption and water film thickness in clayey materials as a function of relative humidity

Abstract

Soil water, with adsorbed water being an important component, plays an important role in fluid flow and chemical movement in the unsaturated zone. The adsorbed water consists of water film and interlayer water, and its content is related to the relative humidity (RH). This study theoretically and experimentally focuses on the variation in adsorbed water content in clayey materials as the RH changes. Based on a slit-pore model, three types of water (water film, interlayer water, and capillary water) could be present in the water vapor adsorption process. The variation of water film is obtained from the analysis of interfacial forces, and then the total water content can be quantitatively subdivided into these three types of water for different RH values. The slit-pore adsorption model was used with experimental measurements (water vapor adsorption and N 2 physisorption) to quantify the amounts and interrelationships of these three different types of water to six clayey materials, namely three clay minerals (kaolinite, montmorillonite, and illite-smectite mixed layer) and three clay-rich sediments from the Jianghan Plain in China. The main results are that (a) the volumes of water vapor adsorption are much greater than those of N 2 adsorption except for kaolinite; (b) interlayer water largely dominates the growth of total water content in montmorillonite and results in a concentration of 0.090 ml g −1 at 95% RH; and (c) the minimum thickness of water film is calculated to be 0.23 nm, and the maximum value is one-third of the pore width by considering the interfacial forces. 1 INTRODUCTION Soil water supports plant growth, affects nutrient transport, and is involved in many geophysical and geochemical

DLVO-Based Analyses of the Water Vapor Adsorption and Condensation in Hydrophilic Nanopores of Low-Rank Coal

“…The electrical double layer between the two interfaces overlaps when the distance between the interfaces is less than the thickness of the Debye layer; then, the electrostatic interactions will be generated. According to Lin et al, 48 the strength of Π e can be expressed as…”

“…The electrical double layer between the two interfaces overlaps when the distance between the interfaces is less than the thickness of the Debye layer; then, the electrostatic interactions will be generated. According to Lin et al, the strength of Π e can be expressed as where ε is the electric permittivity of water, which is the product of vacuum permittivity and the dielectric constant of water, 7.21 × 10 –10 F/m when the temperature is 298 K, k B is the Boltzmann’s constant (1.38 × 10 –23 J/K), e is the electron charge, 1.6 × 10 –19 C, and z is the ion valence.…”

Elucidating the role of water films on solute diffusion in unsaturated porous media by improved pore‐scale modeling

“…The average thickness of water films $$\bar d$$ in unsaturated porous media relates to many factors such as saturation level, humidity, particle/pore size, and surface roughness, and ranges from several nanometers to a few micrometers (Carminati et al., 2008; Gao et al., 2021; Jiang et al., 2020; Lin et al., 2020; Tokunaga et al., 2017). When the thickness of the water film is in the order of some nanometers, the liquid–solid interface, especially the electrical double layer effect, will have a non‐negligible impact on solute transport.…”

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“…For instance, the water layer thickness in the pores will increase during water vapor adsorption. [26] This reduces the available free space or leads to the full saturation of small pores. [6,27,28] The Knudsen effect is then increased and reduces the effective gas diffusion significantly.…”

“…[ 21,29 ] In addition, swelling of the material due to interlayer water further reduces the free space for molecular diffusion. [ 26 ] In cement‐based materials, gas diffusion coefficients at dry state of m 2 s −1 are reduced to m 2 s −1 at high saturation levels above 80%. [ 13,30 ] Odeh et al computed the effective pore radius due to water adsorption and its effect on Knudsen diffusion.…”