Speaker
Description
Volumetric water vapour sorption isotherms have been carried out in nanoporous monolithic glass membranes (Vycor) in both empty and salt solution (Li-/NaCl) filled pores in order to investigate the relative humidity and pore-filling fraction associated with capillary condensation and peak desorption/desorption-tension, and the impact of salt solution activity/chemical nature on such processes. Subsequently, optical reflectance (imaging) measurements have been
conducted on the same systems (Vycor membranes filled with different salt solutions) using a home-made controlled environment (temperature and relative humidity under vacuum) setup in order to identify the thermodynamic signatures of specific processes, such as adsorption/desorption tension activity, formation of salt solution clusters, and crystallisation. The correlation between the volumetric and optical experiments have been investigated to unravel the pore filling/emptying mechanisms, and the role played by salt ions in mediating the transport of water molecules. The results of this analysis have been compared to the ones obtained from molecular dynamics simulations of desorption of salt solutions from an interconnected pore network . Ongoing studies reveal a second order transition from vapour to condensed liquid filled pores for salt solutions, contrary to a clearly defined first order capillary condensation observed for empty pores. Results also indicate that the salt solution clusters develop within the pores during the desorption process strongly retard the escape of water molecules, causing the desorption process to spread over a wide humidity range. Further thermodynamic treatment of the sorption isotherms help attain a clearer understanding of the associated pore-emptying mechanisms, such as homogeneous meniscus recession/cavitation/pore-blocking under a simultaneously occurring ionic-rearrangement of the salt along the pore walls. The next step involved investigating the kinetics of vapour phase imbibition of nanoporous membranes filled with salt solutions, followed by drying once the pore filling reached saturation. In such experiments, the Vycor membranes were sealed on all sides, except one left free for transport of water molecules. This led to a 1D imbibition/drying front, the progress of which could be plotted against time for its analysis by appropriate kinetic models. Preliminary analysis suggests that both wetting and drying processes are significantly retarded when salt is present inside the nanopores. Results also indicate that the drying kinetics is strongly governed by the activity of the confined salt solution, as a dynamically developing humidity gradient along the length of membrane may lead to a gradient in the salt percolation network. At present, evaporation of water from isolated horizontal nanochannels filled with salt solutions is being investigated, which may be connected to vertical nanopores in future studies (in a different nanofluidic device) to quantify the mass transport of water from a single model pore geometry and the impact of salt solution activity/chemical nature on it.
| Participation | In-Person |
|---|---|
| Country | France |
| Energy Transition Focused Abstracts | This abstract is related to Energy Transition |
| MDPI Energies Student Poster Award | Yes, I would like to submit this presentation into the student poster award. |
| Acceptance of the Terms & Conditions | Click here to agree |
