Spreading dynamics of terraced droplets.

Area of Science:

• Materials Science
• Surface Science
• Soft Matter Physics

Background:

• The de Gennes and Cazabat (dGC) model describes the terraced spreading of liquid droplets.
• Understanding droplet dynamics is crucial for thin-film deposition and microfluidics.
• The liquid crystal (-)7S5 on a silicon oxide wafer presents a simplified system for studying terraced spreading.

Purpose of the Study:

• To investigate the applicability and limitations of the dGC model for a two-terraced liquid crystal droplet.
• To analyze the dynamic behavior of droplet spreading, specifically the formation of a central hole.
• To develop an extended dGC model that incorporates the observed hole formation.

Main Methods:

• Experimental observation of (-)7S5 liquid crystal droplet spreading on an oxide-covered (100) Si wafer.
• Analysis of droplet morphology, including terrace thickness and hole development.
• Theoretical modeling using an extended de Gennes and Cazabat (dGC) framework.

Main Results:

• A two-terraced droplet of (-)7S5 liquid crystal was observed spreading on a silicon wafer.
• A central hole spontaneously formed in the upper terrace of the droplet.
• The extended dGC model, including the hole, reasonably described the average spreading dynamics.

Conclusions:

• The dGC model is unstable to hole formation in the upper terrace of a two-terraced droplet.
• The extended dGC model provides a good approximation but struggles with quantitative accuracy due to experimental border irregularities.
• Further model refinement is needed to account for time-dependent irregularities in terrace borders.