Modeling the Influence of Side Stream and Ink Bottle Structures on Adsorption/Desorption Dynamics of Fluids in Long Pores

Abstract

We apply dynamic mean field theory to study relaxation dynamics for lattice models of fluids confined in linear pores with side streams and with ink bottle structures. Our results show several mechanisms for how the pore structure affects the dynamics, and these are amplified in longer pores. An important conclusion of this work is that features such as side streams and ink bottle segments can substantially slow the equilibration of fluids confined in long pore systems where the pore lengths can be more than 100 micrometers, such as in porous silicon. This may make it difficult to properly equilibrate these systems for states close to those where the pores should be completely filled with liquids. The presence of trapped bubbles in the system may change the desorption characteristics of the system and the shape of the hysteresis loops.

Sequential N2 Adsorption by the Nanopore Entrance Filling Scheme in Nanopores of Carbon Nanotubes

“…Condensed molecules adsorbed in the neck parts were then gradually slid and filled into the cavity part. The adsorption mechanism in the ink-bottle pore was also reported elsewhere. ,− Thus, the adsorption mechanism in the ink-bottle pore was phenomenologically similar to the nanopore entrance filling mentioned above (Figure c). However, the necks in the ink-bottle pore were composed of solid carbon walls, whereas the “neck” comprised preadsorbed molecules in the nanopore entrance filling in 3 nm CNTs.…”

“…However, the pore blocking feature was hardly observed because adsorption proceeded without a considerable kinetic adsorption barrier, as mentioned later. The structure of preadsorbed molecules stacked at nanopore entrances looked similar to an ink-bottle pore, ,− indicating the similar adsorption/condensation mechanism at the nanopore entrances of 3 and 5 nm CNTs. In ink-bottle pores, condensation was first observed at the neck and then condensation at the cavity was observed.…”

Modeling the Impact of Mesoporous Silica Microstructures on the Adsorption Hysteresis Loop

“…Several theoretical and numerical models have been developed to study both the density distribution and thermodynamics of fluids in porous materials as well as to describe the sorption hysteresis. − In particular, mean-field density functional theory (MFDFT) applied to lattice fluid models of mesoporous systems provides a coarse grained approach to modeling sorption on length scale approaching experimental conditions. − Developments in electron tomography permit the complementary reconstruction of the morphology of mesoporous materials, offering unprecedented insight into the material structure at nanoscopic length scales. − In a recent paper, we applied MFDFT for calculating nitrogen adsorption–desorption isotherms for a mesoporous silica sample from the skeleton of a hierarchical, macro–mesoporous silica monolith . The reconstructed image of the sample obtained by electron tomography was used directly to build the pore structure used in the MFDFT.…”

Advancing Computational Analysis of Porous Materials—Modeling Three-Dimensional Gas Adsorption in Organic Gels

“…In an effort to advance toward more computationally efficient adsorption analysis, more recent studies have taken a coarse-grain approach using lattice-based mean field theory (MFT), with studies focusing on understanding the adsorption mechanism within individual pores of varying sizes and geometries − and further work extending to adsorption analysis within complex porous structures. , This approach has also been applied to silica gels, using it predominantly as a tool to elucidate the mechanisms behind hysteresis formation. , The work presented here builds upon this approach, applying these lattice-based MFT calculations to three-dimensional simulated porous organic gels to model adsorption analysis within materials produced across a range of synthesis parameters, allowing an extensive range of structures to be explored and analyzed, with a view to enable material tailoring.…”