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Two-Step Wetting of Nanoporous Carbons: Small-Angle Scattering Analysis of Capillary Rise
François Chaltin1, Martin Rosenthal2,3, Alexandre F Léonard4
1Department of Chemical Engineering, University of Liège, B6A, Allée du Six Août 13, 4000 Liège, Belgium.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 20, 2024
Summary
Water wetting in nanoporous materials occurs in two steps: first filling micropores, then mesopores. Micropore filling transforms hydrophobic mesopores into hydrophilic ones, enabling classical wetting models for these carbon xerogels.
Area of Science:
- Materials Science
- Nanotechnology
- Physical Chemistry
Background:
- Nanoporous materials are crucial for many applications, often requiring liquid filling.
- Understanding the wetting behavior of liquids in nanometer-sized pores is technologically vital but poorly understood.
Purpose of the Study:
- To investigate the wetting process of water in nanoporous carbon xerogels at the nanoscale.
- To elucidate the phenomenology and conditions governing liquid imbibition in confined nanoporous structures.
Main Methods:
- Capillary rise experiments were conducted with water in carbon xerogels.
- Synchrotron small-angle X-ray scattering (SAXS) was employed for in situ nanoscale observation.
- Cassie-Baxter analysis was used to determine contact angles and surface properties.
Main Results:
- A distinct two-step wetting process was observed: initial water permeation into micropores followed by mesopore imbibition.
- Water presence in micropores was found to alter mesopore surface properties from hydrophobic to hydrophilic.
- Wetting kinetics in mesopores were quantitatively described by the Washburn model.
Conclusions:
- The study reveals a two-step wetting mechanism in nanoporous materials, influenced by pore size and surface chemistry.
- The transformation of mesopore wettability by micropore filling is a key factor in the overall wetting process.
- Surface barriers hinder water transfer from mesopores to micropores, impacting imbibition dynamics.
