Phase transitions in disordered mesoporous solids

Abstract

Fluids confined in mesoporous solids exhibit a wide range of physical behavior including rich phase equilibria. While a notable progress in their understanding has been achieved for fluids in materials with geometrically ordered pore systems, mesoporous solids with complex pore geometries still remain a topic of active research. In this work we study phase transitions occurring in statistically disordered linear chains of pores with different pore sizes. By considering, quite generally, two phase change mechanisms, nucleation and phase growth, occurring simultaneously we obtain the boundary transitions and the scanning curves resulting upon reversing the sign of the evolution of the chemical potential at different points along the main transition branches. The results obtained are found to reproduces the key experimental observations, including the emergence of hysteresis and the scanning behavior. By deriving the serial pore model isotherm we suggest a robust framework for reliable structural analysis of disordered mesoporous solids.

Comparative Gas Sorption and Cryoporometry Study of Mesoporous Glass Structure: Application of the Serially Connected Pore Model

“…Microscopic details of how these effects emerge in long chains were explored using combinations of only few pore sections using GCMS simulations (Nguyen et al, 2013a). Analogous studies, but with notably longer chains, have proven the emergence of cooperativity effects and validated the conclusions made earlier (Kondrashova and Valiullin, 2013, 2015; Schneider et al, 2017).…”

“…Similarly, for the desorption transition one has to consider two products of (i) the equilibrium kernel θ g ( x, p ) with the PSD of the empty sections and of (ii) the metastable kernel θn′(x,p) with the PSD of the filled sections. An approximate solution for Equations (2) and (3) is presented in the work by Schneider et al (2017) and the exact derivation can be found elsewhere (Schneider and Valiullin, submitted). In what follows, we present the final results.…”

“…Moreover, because of the simplicity of SCPM, it turns out that the problem of phase transitions with included cooperativity effects can be solved analytically, namely, the transition equation (e.g., isotherm in the context of capillary condensation phenomena) can be derived. The first formulation of the theoretical model related to SCPM (Kondrashova et al, 2016) and its solution (Schneider et al, 2017) have been presented recently. In this work, we show the first application of the SCPM theory for structural analysis of a disordered mesoporous silica material.…”

An experimental and modelling study of water vapour adsorption on SBA-15

“…The presence of irregularities in the SBA-15 mesoporous channels was also suggested from diffusion studies by means of pulse field gradient nuclear magnetic resonance [33]. In this view, the sub-domains inside the same pore can no longer be considered independent of each other and the predicted isotherms resemble the isotherms usually obtained on solids characterized by disordered pore networks [34]. To account for the interactions among the sub-domains, the phenomena of advanced adsorption/condensation and pore blocking have been introduced respectively for the adsorption and desorption mechanisms.…”

“…The first formulation of the model considers a solid made of regular independent cylindrical pores. The second formulation of the model considers nonregular independent cylindrical pores for an improved correlation of the scanning curves, which is similar to the serially connected pore model [34].…”