Rupture of ultrathin solution films on planar solid substrates induced by solute crystallization.

Area of Science:

• Materials Science
• Physical Chemistry
• Fluid Dynamics

Background:

• Understanding the rupture of ultra-thin films is crucial for applications involving thin-film deposition and coating.
• Binary mixtures of volatile solvents and nonvolatile solutes present complex thinning and rupture dynamics.

Purpose of the Study:

• To investigate the rupture behavior of ultra-thin films composed of binary solvent-solute mixtures during spin casting.
• To determine the factors influencing the critical rupture thickness (h_rupture) of these films.
• To establish a universal model for film rupture behavior.

Main Methods:

• On-line optical imaging of continuously thinning planar films in a spin cast configuration.
• Systematic variation of initial solute concentrations (c₀) in binary mixtures.
• Analysis of film rupture thickness (h_rupture) as a function of c₀.

Main Results:

• Pure solvents completely wet silica substrates.
• Solution films rupture at a thickness dependent on initial solute concentration (c₀).
• At low c₀, h_rupture is proportional to c₀; at high c₀, h_rupture is approximately 50 nm, independent of c₀.
• Solute crystallization at the liquid/substrate interface upon supersaturation drives localized film rupture.
• A rescaled data analysis reveals a universal rupture behavior across different solvent/solute mixtures.

Conclusions:

• Solute enrichment and subsequent crystallization at the substrate interface govern ultra-thin film rupture.
• The findings provide a unified understanding of rupture phenomena in diverse binary solvent-solute systems.
• This work offers insights into controlling thin-film stability and rupture in material processing.