Related Experiment Video
Updated: May 16, 2026
07:18
Measuring the Interaction Force Between a Droplet and a Super-hydrophobic Substrate by the Optical Lever Method
Published on: June 14, 2019
Dynamic measurement of the force required to move a liquid drop on a solid surface
D W Pilat1, P Papadopoulos, D Schäffel
1Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 28, 2012
Summary
Researchers measured the forces needed to slide water drops across surfaces using a novel instrument. They found adhesion forces increase with drop size and sliding speed, revealing insights into liquid-surface interactions.
Area of Science:
- Fluid dynamics
- Surface science
- Materials science
Background:
- Understanding liquid-solid interactions is crucial for various applications, including microfluidics and coatings.
- Quantifying adhesion forces of sessile drops is essential for predicting their behavior on surfaces.
Purpose of the Study:
- To measure the dynamic lateral adhesion forces of sessile water drops on different surfaces.
- To investigate the relationship between adhesion force, drop volume, sliding velocity, and surface properties.
Main Methods:
- Utilized a drop adhesion force instrument (DAFI) to measure forces on water drops (0.1–2 μL).
- Employed a vertical deflectable capillary inserted into the drop to measure dynamic lateral adhesion.
- Studied forces on flat polydimethylsiloxane (PDMS) surfaces and a 3D superhydrophobic pillar array.
Main Results:
- On PDMS, dynamic lateral adhesion force increased linearly with contact area diameter and sliding velocity.
- Observed pinning of the three-phase contact line to individual surface defects.
- On superhydrophobic surfaces, simultaneous depinning from multiple pillars caused force peaks.
Conclusions:
- The DAFI provides a method for dynamic adhesion force measurement.
- Adhesion forces are predictable based on drop size and velocity on homogeneous surfaces.
- Surface topography significantly influences adhesion dynamics, especially on superhydrophobic structures.
Related Concept Videos
01:22Surface Tension of Fluid
Surface tension is a fundamental property of fluids, occurring at the boundary between a liquid and a gas or between two immiscible liquids. This phenomenon arises from the cohesive forces between molecules at the fluid's surface, creating an effect similar to a stretched elastic membrane. Inside each fluid, molecules are equally attracted in all directions by neighboring molecules, but surface molecules experience a net inward force, resulting in surface tension.
Surface tension varies with...
Surface tension varies with...
02:57Surface Tension, Capillary Action, and Viscosity
Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
01:20Stokes' Law
Viscous forces, like friction, are intermolecular forces that resist the relative motion of molecules over each other. When a solid body moves through a liquid, viscous forces drag it in the opposite direction. The force's magnitude depends on the solid's shape and size, as well as its speed and the liquid's coefficient of viscosity, density and temperature.
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...
01:16Measurement of Fluid Pressure
Fluid pressure is commonly measured using devices called manometers, which rely on liquid columns to indicate pressure differences. The height of a liquid column in a manometer reflects the pressure exerted by the fluid, providing a simple yet effective means of measurement. Different types of manometers serve specific purposes based on their configurations and the type of fluids involved.
A basic form of manometer is the piezometer, a vertical tube open at the top and filled with the same...
A basic form of manometer is the piezometer, a vertical tube open at the top and filled with the same...
01:16Surface Tension and Surface Energy
When a paint brush is immersed in water, the bristles wave freely inside the water. When it is taken out, the bristles stick together. The reason behind this effect is surface tension.
Consider a beaker filled with liquid. The bulk molecules in the liquid experience equal attractive forces on all sides with the surrounding molecules. However, the surface molecules experience a net attractive force downward due to the bulk molecules. The surface of the liquid behaves like a stretched membrane,...
Consider a beaker filled with liquid. The bulk molecules in the liquid experience equal attractive forces on all sides with the surrounding molecules. However, the surface molecules experience a net attractive force downward due to the bulk molecules. The surface of the liquid behaves like a stretched membrane,...
01:27Dimensional Analysis
Dimensional analysis is a valuable technique in fluid mechanics for simplifying complex problems by reducing them into dimensionless groups. These groups capture the essential relationships between the variables involved, allowing researchers and engineers to analyze fluid flow without dealing with each variable individually. This approach reduces the number of independent variables, allowing for easier analysis and better understanding of physical phenomena.
In fluid mechanics, dimensional...
In fluid mechanics, dimensional...