Experimentally probing ionic solutions in single-digit nanoconfinement

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Understanding ionic solutions in nanoconfinement is key to explaining behavioral transitions.
• Classical theories struggle when system length scales approach ionic solution energetics and equilibrium near surfaces.

Purpose of the Study:

• To experimentally probe ion transport and distribution in single-digit nanoconfinement.
• To investigate the influence of cation kosmotropic properties on behavior within nanochannels.
• To develop and utilize a novel characterization technique for nanoconfined solutions.

Main Methods:

• Utilized a test vehicle with 3 and 5 nm silica nanochannels.
• Employed interface hard X-ray reflectivity analysis for direct probing.
• Investigated solutions with cations of increasing kosmotropic properties (BaCl2, CaCl2, MgCl2).

Main Results:

• Cation adsorption decreases with decreasing confinement size; smaller cations show favored adsorption.
• Nanochannel clogging was observed, linked to ion pair formation.
• Ion pairs act as prenucleation clusters, potentially leading to phase precipitation.

Conclusions:

• Specific ion effects significantly alter solution properties in single-digit nanoconfinement.
• The developed method offers new possibilities for characterizing ionic solutions and interfaces at the nanoscale.
• Observed phenomena challenge classical models at these reduced length scales.