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Oil and water don’t mix, as you’ve seen. You and I get wet, but ducks don’t. Water adheres to mercury, but it does not wet the glass; oil rises in a cotton wick against gravity; sap and water rise to the top of the tree’s leaves, and paintbrush hairs don’t cling together when dry or even when dipped in water but form a fine tip when removed. All of these occurrences and a bunch of others are connected to the free surfaces of liquids. When liquids are poured into a container, they acquire a free surface since they have no defined shape but have a specified volume. These surfaces have a little extra boost. Surface tension is the term for this phenomenon, which only applies to liquids because gases do not have free surfaces. Let’s look at how surface tension works and how it affects us.
What is Surface Tension?
A force per unit of length (or surface energy per unit area) operating in the plane of the liquid-solid interface and any other material is known as surface tension. It is also the additional energy that molecules at the interface have over molecules in the interior. The formula of surface tension is-
γ = F/L
As a result, surface tension can be measured in units of energy (joules) per unit area (square metres). At 20 °C (68 °F), water has a surface tension of 0.07275 joules per square metre. Organic liquids with lower surface tensions, such as benzene and alcohols, have a lower surface tension than mercury, which has higher surface tension. The net force of attraction between molecules decreases as the temperature rises, lowering surface tension.
The excess potential energy of the molecules on the surface compared to their potential energy on the inside causes surface tension. At the interface separating two substances, at least one of which is a fluid, such surface energy exists. It isn’t only a property of a single liquid.
Effect of Surface Tension in everyday life
Surface tension is essential in many common phenomena: it causes little raindrops to adhere to your windows, generates bubbles in your sink when you add detergent, and pushes water-striding insects over pond surfaces. With ordinary water, there are several impacts of surface tension:
Rainwater beads on a waxy surface like a leaf. Water clusters into drops because it sticks weakly to wax but firmly to itself. Because a sphere has the smallest possible surface area to volume ratio, surface tension gives them its near-spherical shape.
When a liquid mass is stretched, drop formation happens. The water clings to the faucet and developing group until the surface tension can no longer keep the drop attached to the faucet. The drop then separates and is shaped into a sphere by surface tension. If a stream of water were to come out of the tap, it would break up into droplets as it descended. The stream is stretched by gravity and then compressed by surface tension into spheres.
Flotation of non-wettable items denser than water happens when the object’s weight is minimal enough to be supported by surface tension forces. Water striders, for example, walk on a pond’s surface using surface tension in the following fashion: Because there is no connection between the molecules of the water strider’s leg and the water molecules. When the leg presses down on the water, the surface tension of the water seeks to recover its flatness from the leg’s deformation. The water strider is pulled upward by the water’s behaviour, allowing it to stand on its surface as long as its mass is small enough for the water to support it. The water’s surface behaves like an elastic film: the insect’s feet make indentations in the surface, increasing the water’s surface area. In contrast, the water’s inclination to minimise surface curvature (space) pushes the insect’s feet higher.
Tension at the surface between different liquids causes oil and water separation (in this case, water and liquid wax). The term “interface tension” is used to describe this form of surface tension, but the chemistry is the same.
Wine tears are droplets and rivulets that form on the side of a glass containing an alcoholic beverage. It is caused by a complex interplay between the various surface tensions of water and ethanol, created by a combination of ethanol changing the surface tension of water and ethanol evaporating quicker than water.
Conclusion
Surface tension is the amount of energy necessary to raise the surface area by a certain quantity. The requirement for this to happen is that strong intermolecular interactions exist between distinct liquid particles. The phenomenon known as surface tension is caused by the cohesive forces between liquid molecules. Because other water molecules do not entirely encircle the molecules at the surface of a glass of water on all sides, they are called surface molecules. They cohere more strongly with those directly related to them (in this case, next to and below them, but not above). It is not true that a “skin” forms on the water surface; the stronger cohesiveness between water molecules, as opposed to the attraction of water molecules to the air. It is more difficult to move an object through the surface than it is to move it while completely immersed.
