A Model for Detachment of a Partially Wetting Drop from a Solid Surface by Shear Flow

Area of Science:

• Fluid Dynamics
• Surface Science
• Materials Science

Background:

• Liquid drop detachment from surfaces is crucial in various industrial processes.
• Understanding detachment mechanisms under shear flow requires analyzing dynamic contact angles and forces.
• Existing models often simplify the complex interplay of forces governing drop behavior.

Purpose of the Study:

• To model liquid drop detachment from a solid surface subjected to simple shear flow.
• To differentiate detachment mechanisms based on the drop's equilibrium contact angle and shear rate.
• To validate the model using experimental data for Pristane and Squalane drops.

Main Methods:

• Development of an approximate mathematical model for partially wetting drop detachment.
• Analysis of drop deformation, dynamic contact angles, and forces (drag, retentive, lift, adhesive, gravitational, buoyancy).
• Comparison of model predictions with experimental data for different liquid drops (Pristane, Squalane).

Main Results:

• Drop detachment occurs when shear flow drag overcomes retentive forces or when lift force balances other forces.
• Drops with high equilibrium contact angles (near 180°) detach via sliding.
• Drops with lower equilibrium contact angles detach via lift force at higher shear rates.

Conclusions:

• The developed model accurately predicts drop detachment modes (sliding vs. lift) based on equilibrium contact angle.
• Pristane drop detachment (high contact angle) is well-modeled by sliding, while Squalane drop detachment (lower contact angle) is well-modeled by lift.
• The study provides a framework for understanding and predicting liquid drop behavior in shear flows.