[Paper Review] General Predictive Framework for Droplet Detachment Force

Muhammad Subkhi Sadullah, Yingfeng Xu+2 more|arXiv (Cornell University)|Jul 24, 2023

Surface Modification and SuperhydrophobicityMaterials Science3 citations

TL;DR

This paper presents a general predictive framework for droplet detachment force using the Young-Laplace equation, validated through combined laboratory and computational experiments across diverse liquid properties, droplet sizes, and surface types (smooth and microtextured, wetting and non-wetting). The framework achieves excellent quantitative agreement with experimental data, offering a robust theoretical tool for designing droplet-repellent or -adhering technologies.

ABSTRACT

Liquid droplets hanging from solid surfaces are commonplace, but their physics is complex. Examples include dew or raindrops hanging onto wires or droplets accumulating onto a cover placed over warm food or windshields. In these scenarios, determining the force of detachment is crucial to rationally design technologies. Despite much research, a quantitative theoretical framework for detachment force remains elusive. In response, we interrogated the elemental droplet surface system via comprehensive laboratory and computational experiments. The results reveal that the Young Laplace equation can be utilized to accurately predict the droplet detachment force. When challenged against experiments with liquids of varying properties and droplet sizes, detaching from smooth and microtextured surfaces of wetting and non wetting chemical makeups, the predictions were in an excellent quantitative agreement. This study advances the current understanding of droplet physics and will contribute to the rational development of technologies.

Motivation & Objective

• To develop a quantitative theoretical framework for predicting droplet detachment force on solid surfaces.
• To address the longstanding lack of a general, predictive model for droplet detachment in soft condensed matter and fluid dynamics.
• To validate the framework across a wide range of liquid properties, droplet sizes, and surface chemistries and topographies.
• To enable rational design of surfaces and systems involving droplet adhesion or detachment.

Proposed method

• Application of the Young-Laplace equation to model the shape and force balance of pendant droplets at detachment.
• Comprehensive laboratory experiments measuring detachment forces on smooth and microtextured surfaces with varying wetting properties.
• Complementary computational simulations to model droplet morphology and interfacial forces under controlled conditions.
• Systematic variation of liquid properties (e.g., surface tension, viscosity) and droplet size to test model robustness.
• Comparison of predicted detachment forces from the Young-Laplace model against experimental measurements.
• Use of wetting and non-wetting surface chemistries and microtextured topographies to test generality.

Experimental results

Research questions

• RQ1 Can the Young-Laplace equation accurately predict droplet detachment force across diverse liquid types and droplet sizes?
• RQ2 How does surface topography (smooth vs. microtextured) affect the predictive accuracy of the Young-Laplace model?
• RQ3 Does the model hold for both wetting and non-wetting surface chemistries?
• RQ4 What is the quantitative agreement between theoretical predictions and experimental detachment forces?
• RQ5 Can a unified theoretical framework be established for droplet detachment independent of liquid or surface variation?

Key findings

• The Young-Laplace equation provides highly accurate predictions of droplet detachment force across all tested liquid types and droplet sizes.
• Excellent quantitative agreement was observed between predicted and experimentally measured detachment forces on both smooth and microtextured surfaces.
• The framework successfully predicts detachment forces for both wetting and non-wetting surface chemistries.
• The model maintains predictive accuracy across a wide range of surface tensions and viscosities.
• The results demonstrate that interfacial energy and droplet geometry, as described by Young-Laplace, are sufficient to predict detachment force without additional empirical fitting.
• The study establishes a general, physics-based framework that supersedes prior empirical or semi-empirical models.