What Is Surface Tension

Causes of Surface Tension

Surface tension allows a liquid's surface to resist external forces, playing a key role in various natural and technological processes.

Surface tension is primarily caused by the cohesive forces between liquid molecules. In liquids like water, hydrogen bonds create strong attractions among molecules, especially at the surface. These intermolecular forces cause the surface to behave like a stretched elastic membrane, minimizing the surface area and maintaining the integrity of the liquid's surface.

Measurement of Surface Tension

Accurate measurement of surface tension is essential in both scientific research and industrial applications. Several methods are commonly used:

Capillary Rise Method

This technique measures the height a liquid climbs in a narrow tube due to surface tension. The height is directly related to the surface tension and can be calculated using established formulas.

Du Noüy Ring Method

In this method, a ring is gently lowered onto the liquid surface and then lifted. The force required to detach the ring from the liquid provides a measure of the surface tension.

Wilhelmy Plate Method

A thin plate is submerged vertically into the liquid, and the force exerted on the plate by the liquid's surface tension is measured. This force is used to determine the surface tension value.

For more information, please check Stanford Advanced Materials (SAM).

How to Break Surface Tension

Breaking or reducing surface tension involves disrupting the cohesive forces between liquid molecules. Common approaches include:

• Adding Surfactants: Surfactants are compounds that lower surface tension by interfering with the hydrogen bonds between liquid molecules.
• Increasing Temperature: Heating a liquid can weaken intermolecular forces, thereby reducing surface tension.
• Mechanical Agitation: Stirring or shaking a liquid introduces energy that disrupts the surface layer, decreasing surface tension.

Examples of Surface Tension in Nature and Technology

Surface tension is evident in numerous natural phenomena and technological applications:

• Water Striders: These insects utilize surface tension to walk on water without sinking.
• Formation of Droplets: Surface tension causes liquids to form spherical droplets, minimizing surface area.
• Inkjet Printing: The formation and ejection of ink droplets rely on precise control of surface tension.
• Detergents: Surfactants in detergents reduce surface tension, enhancing the cleaning process by allowing water to spread and penetrate surfaces more effectively.

Frequently Asked Questions

What is surface tension?

Surface tension is the property of a liquid that allows its surface to resist external forces, caused by cohesive forces between molecules.

How is surface tension measured?

It is measured using methods like the capillary rise, Du Noüy ring, and Wilhelmy plate techniques, each involving different approaches to quantify the force per unit length.

What causes surface tension in water?

In water, hydrogen bonds between molecules create strong cohesive forces, leading to surface tension.

How do surfactants affect surface tension?

Surfactants lower surface tension by disrupting the cohesive forces between liquid molecules, making it easier for liquids to spread and mix.

Can temperature change surface tension?

Yes, increasing temperature generally decreases surface tension by weakening the cohesive forces among molecules.