Missing Eutectic Transition in Electrolyte Solutions in Confinement Due to Ion Accumulation in the Interfacial Layer.

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Aqueous electrolytes exhibit unusual behavior under nanoconfinement.
• Eutectic transitions in nanoporous dilute solutions are often inhibited.
• Understanding these anomalies is crucial for natural and industrial processes.

Purpose of the Study:

• To investigate the reasons behind the inhibited eutectic transition in confined electrolyte solutions.
• To identify the key factors controlling salt crystallization under nanoconfinement.
• To elucidate the role of interfacial layers in ion distribution and phase behavior.

Main Methods:

• Calorimetric measurements of CaCl2 and NaCl solutions.
• Systematic studies using nanoporous silica with varying pore sizes.
• Controlled variation of salt concentration and pore filling degree.

Main Results:

• Eutectic transition is inhibited when the interfacial layer is ion-unsaturated.
• Absence of salt crystallization occurs in solutions with insufficient ion supply.
• Simultaneous ice and salt crystallization at the eutectic point is observed in saturated interfacial layers and concentrated core solutions.
• Pore size, salt concentration, and filling degree critically control the eutectic transition.

Conclusions:

• Preferential ion accumulation in interfacial layers dictates phase behavior in nanoconfined electrolytes.
• Ion depletion in the pore core contributes to the absence of salt crystallization.
• Interfacial layer saturation is key for observing the eutectic transition under nanoconfinement.