Related Experiment Video
Updated: Aug 11, 2026
07:08
Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films
Published on: August 18, 2018
Experiments on the motion of drops on a horizontal solid surface due to a wettability gradient
Nadjoua Moumen1, R Shankar Subramanian, John B McLaughlin
1Department of Chemical and Biomolecular Engineering, Clarkson University, Potsdam, New York 13699, USA.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 8, 2006
Summary
Researchers studied the movement of tetraethylene glycol drops on a silicon surface with a controlled wettability gradient. A theoretical model generally matched experimental drop velocities, with adjustments for hysteresis improving predictions.
Area of Science:
- Surface Science
- Fluid Dynamics
- Materials Science
Background:
- Understanding fluid behavior on surfaces with varying properties is crucial in many scientific and industrial applications.
- Wettability gradients significantly influence droplet dynamics, presenting complex challenges for theoretical modeling.
- Previous models often struggled to accurately predict droplet motion in non-uniform surface energy environments.
Purpose of the Study:
- To experimentally investigate the motion of tetraethylene glycol drops on a silicon surface featuring a controlled wettability gradient.
- To compare experimental results with predictions from a recently developed quasi-steady theoretical model.
- To refine the theoretical model by incorporating factors like contact angle hysteresis to improve prediction accuracy.
Main Methods:
- Creating a wettability gradient on silicon wafers using dodecyltrichlorosilane vapor exposure.
- Capturing high-resolution video images of moving tetraethylene glycol drops along the gradient.
- Analyzing video data to determine drop size and velocity as a function of position.
- Measuring static contact angles to quantify the local wettability gradient.
Main Results:
- Droplet velocity exhibited a strong dependence on the position along the wettability gradient.
- A quasi-steady theoretical model, balancing hydrodynamic resistance and driving force, generally aligned with experimental observations.
- Discrepancies between observed and predicted velocities were significantly reduced when the model accounted for contact angle hysteresis.
Conclusions:
- The quasi-steady theoretical model provides a reasonable framework for understanding droplet motion on wettability gradients.
- Contact angle hysteresis plays a critical role in droplet dynamics and must be considered for accurate theoretical predictions.
- Further refinement of models incorporating surface energy effects can enhance the predictability of fluid behavior on engineered surfaces.
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...
01:19Capillarity in Fluid
Capillarity describes the movement of liquid in small spaces without external forces acting on it. The capillarity is driven by surface tension and adhesive interactions between the liquid and surrounding solid surfaces. This effect is often seen in narrow tubes, porous materials, and fine particles.
Surface tension is crucial to capillarity. It results from cohesive forces between liquid molecules at the liquid-air boundary, forming a skin that resists external forces. When the capillary tube...
Surface tension is crucial to capillarity. It results from cohesive forces between liquid molecules at the liquid-air boundary, forming a skin that resists external forces. When the capillary tube...
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...
01:18Rise of Liquid in a Capillary Tube
When very thin cylindrical tubes, called capillaries, are dipped in a liquid, the liquid rises or falls in the tube compared to the surrounding liquid. This phenomenon is called capillary action. Capillary action occurs due to the combination of two opposing forces: the cohesive forces of the liquid, which cause it to stick to itself and form a rounded shape, and the adhesive forces between the liquid and the walls of the container, which cause the liquid to be attracted to the container walls.
01:17Viscosity
When water is poured into a glass, it falls freely and quickly, whereas if honey or maple syrup is poured over a pancake, it flows slowly and sticks to the surface of the container. This difference in the flow of different kinds of liquids arises due to the fluid friction between the liquid layers and the liquid and the surrounding material. This property of fluids is called fluid viscosity. In this example, water has a lower viscosity than honey and maple syrup.
The SI unit of viscosity is...
The SI unit of viscosity is...
01:13Excess Pressure Inside a Drop and a Bubble
The shape of a small drop of liquid can be considered spherical, neglecting the effect of gravity. This drop can further be considered as two equal hemispherical drops put together due to surface tension. The forces acting on the spherical drop are due to the pressure of the liquid inside the drop, the pressure due to air outside the drop, and the force due to the surface tension acting on the two hemispherical drops.