Related Experiment Video
Updated: May 8, 2026
10:22
High Speed Droplet-based Delivery System for Passive Pumping in Microfluidic Devices
Published on: September 2, 2009
Trapped liquid drop at the end of capillary
Zhengjia Wang1, Hung-Yu Yen, Cheng-Chung Chang
1Department of Chemical and Materials Engineering, National Central University , Jhongli, Taiwan 320, R.O.C.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 6, 2013
Summary
Contact angle hysteresis (CAH) significantly influences liquid drop behavior in capillary valves and pendant drop tests. CAH alters contact angles, enhancing capillary forces and modifying drop shapes, impacting valving pressure and drop stability.
Area of Science:
- Fluid dynamics
- Surface science
- Materials science
Background:
- Liquid drops at capillary ends are crucial in capillary valves and pendant drop techniques.
- Contact line pinning and contact angle hysteresis (CAH) affect drop behavior.
- Understanding these phenomena is key for controlling fluid flow and drop stability.
Purpose of the Study:
- To theoretically and experimentally investigate the behavior of liquid drops captured at capillary ends.
- To analyze the impact of contact angle hysteresis (CAH) on drop shape and capillary forces.
- To determine the influence of CAH on valving pressure in capillary valves and drop regimes in pendant drop tests.
Main Methods:
- Theoretical analysis of capillary forces and drop equilibrium.
- Experimental investigation of liquid drop behavior.
- Surface Evolver simulations for modeling drop shapes.
- Comparison of simulation results with experimental data.
Main Results:
- Contact line pinning allows the lower contact angle to exceed the intrinsic angle.
- Contact angle hysteresis (CAH) enables the upper contact angle to decrease, increasing capillary force.
- CAH elevates valving pressure in capillary valves due to enhanced capillary force.
- In pendant drops, CAH leads to four distinct regimes, including a 'light bulb' shape with lower contact angles >180°.
- Simulations and experiments showed good agreement.
Conclusions:
- The coupling between upper and lower contact angles dictates the equilibrium shape of captured drops.
- CAH plays a critical role in modifying capillary forces and drop stability.
- The findings are relevant for designing capillary valves and understanding pendant drop behavior.
Related Concept Videos
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.
01:19Capillarity 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...
01:28Capillary Exchange
The cardiovascular system's chief role is to disseminate gases, nutrients, waste, and other substances to the body's cells. Small molecules like gases, lipids, and lipid-soluble substances directly diffuse through capillary wall endothelial cell membranes. Glucose, amino acids, and ions, including sodium, potassium, calcium, and chloride, use transporters for facilitated diffusion via membrane-specific channels. Glucose, ions, and bigger molecules may also pass through intercellular clefts.
01:20Capillary Beds
Capillary beds are networks of tiny blood vessels that play a crucial role in the circulatory system. These beds are where the exchange of gases, nutrients, and waste products occurs between the blood and surrounding tissues. Each capillary bed consists of numerous capillaries, which are the smallest blood vessels in the body, typically only one cell-thick. This thinness allows for the efficient diffusion of substances.
Capillaries connect arterioles, small branches of arteries, to venules,...
Capillaries connect arterioles, small branches of arteries, to venules,...
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...
01:13Excess 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.