Multilayer adsorption and wetting of acetone on graphite

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Understanding thin film growth and phase transitions is crucial for materials science and nanotechnology.
• Acetone adsorption on graphite provides a model system for studying two-dimensional (2D) phase behavior.

Purpose of the Study:

• To investigate the adsorption/desorption isotherms of acetone on highly oriented pyrolytic graphite (HOPG) above its bulk triple point.
• To characterize the 2D phase behavior, including monolayer formation and multilayer growth.
• To explore prewetting transitions and their impact on film structure and dynamics.

Main Methods:

• Ellipsometry was employed to measure adsorption/desorption isotherms.
• Experiments were conducted at various temperatures above the bulk triple point of acetone.

Main Results:

• Conventional 2D gas-liquid and 2D liquid-solid coexistence regions were observed in the monolayer and submonolayer regimes.
• Multilayer growth occurred layer-by-layer on top of the completed monolayer.
• A prewetting-type transition was identified between 190 K and the triple point, characterized by a thin-thick jump during adsorption and layer-wise desorption.

Conclusions:

• The first adsorbed monolayer of acetone on graphite solidifies with perpendicular molecular orientation below the triple point.
• Higher adsorbed layers form orientationally disordered polar liquids.
• The observed prewetting transition highlights complex interfacial phenomena in 2D film formation.