Nanoscale Capillary Freezing of ionic liquids confined between metallic interfaces

Par Jean Comtet, Laboratoire de Physique Statistique, Ecole Normale Supérieure

Mardi 13  Mars, 14h, Salle des séminaires (215), 2ème étage, Bâtiment A4N

Abstract :

Ionic liquids are composed of equal amount of positive and negative ions, without any solvent. They recently received considerable attention as a new class of materials with fundamental importance for energy storage and active lubrication. Their unique properties result from the competition of strong electrostatic interactions with properly designed molecular structure to avoid crystallization at room temperature. They are however unusual liquids, which challenge fundamentally the classical frameworks of electrolytes. In this talk, we show how we can use quartz tuning fork based AFM nanorheological measurements to explore the properties of ionic liquids in nanometric confinement. We unveil a dramatic change of the ionic liquid towards a solid-like phase below a threshold thickness, pointing to capillary freezing in confinement. This threshold thickness is found to be intimately related to the metallic nature of the confining materials, with more metallic surfaces facilitating capillary freezing. We interpret this behavior in terms of the shift of the freezing transition, taking into account the influence of the electronic screening on ionic liquid wetting of the confining surfaces.