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Define Surface Tension and Surface Energy
Let us define surface tension and surface energy. Everything is composed of molecules. All molecules exhibit varying degrees of attraction to each other. Because of this intermolecular attraction, the molecules in your drink, including the ice in it, stick together in a glass on your tabletop rather than falling apart in the air. The attraction force exerted by the molecules at the surface of the liquid towards one another is known as its surface tension.
Surface energy is the force present in the molecules on the surface of a substance. This force of attraction forms a cohesive structure. The term “surface tension” is typically used in relation to liquids. Likewise, surface energy is talked about when we mention solids. However, they both are exactly the same. To know more about this, let us obtain the relation between surface tension and surface energy.
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How to obtain the relation between surface tension and surface energy?
Surface energy refers to the work done per square inch by the force that forms the surface. The forces that bind liquid molecules create the phenomenon that is known as surface tension. To determine the relationship to surface tension and energy, think of a film of liquid produced within the rectangular frame ABCD in which the crosspiece BC with length L could slide easily between the lengths of DC and AB.
Since liquid surfaces behave like a stretched membrane and are prone to contract, surface tension will be felt on every part of BC at a right angle and tangential to the film’s surface. In the course of this force, the arm BC will move towards AD that of the frame. To hold the wire to its place, the same force must apply in a reverse direction. If the surface tension is T and the length of BC = l, that means the force inward on BC caused by surface tension is
F = 2L x T
Because the film has two surfaces: one at the top and one on the bottom, the length, also known as BC, equals 2L. To ensure that the BC is constant, the same force opposing surface tension must be applied.
The force needed to maintain the wire to its location, F = 2LT
The arm BC is moved slowly, over an angle of x perpendicular to its length, to reach the BC position.
The task was performed against the surface tension,
W= Force x displacement is F x X = 2LTx
The work that is done to enhance the size of its film is unity = Work/Increase of Area
= W / (2/x) = (2LTx) / (2Lx) = T
Where 2Lx represents the total increase in surface (2 is taken to represent both surfaces on the film)
However, work is being performed for the purpose of increasing the size by one as the potential energy per square metre is surface energy. We can therefore draw the conclusion that the tension on the surface is equivalent to the energy of the surface.
Examples to determine the relationship between surface tension and surface energy
To determine the relationship between surface tension and surface energy, you will notice if a ring made of wire is submerged in soap solution before being brought out? There will be soap film thinly forming within the rings.
When the ring of wire is positioned on the film or soap water, the external and internal force tangentially affects every point on the ring, the two forces balance out each of their respective forces, and the ring remains there in a circular form with a soap film.
The relationship between surface tension and surface energy
Surface energy and tension are crucial as they are quantities that show the strength of attraction between molecules. The most powerful surface energy (or tension) substances are those with high boiling points; they must be heated up to counteract the intermolecular attraction to create steam or vapour.
Consider a soap film that is isothermally stretched in an area enclosed with a rectangular-shaped frame, ABCD, and a cross-piece Q. This piece can slide along the frame smoothly. Let T be soap solution’s surface tension, and PQ the length of the wire that is in contact with a soap film.
The film has two surfaces that are in direct contact with the wire. The film can contract by exerting a force upon wire PQ. Because such a surface exerts force TL on the wire, the total force on it is 2L. Let us say the wire PQ was pulled outward slowly, to P’Q’ through a distance Dx. The film’s force was against the wire PQ.
W= applied force x displacement.
The film’s area will increase due to the displacement. Due to the film having two surfaces, its surface area increases.
A=2Ldx
The work done per unit area thus is
W/A = 2TLdx/2Ldx =T
This work is stored in a unit surface area as potential energy. This potential energy can be called the surface.
The above relationship shows that the surface tension is equal in surface energy per unit of liquid. This is the place where surface tension and surface energy create adhesion.
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Conclusion
Surface tension and energy are two measures of intermolecular force that make up a substance. Because of these intermolecular factors, liquid surfaces are always being pulled inward. It is necessary to work with the intermolecular force to stretch the liquid surface. The pressure on the liquid’s surface and the amount required to stretch it can be measured. These measurements correspond with the surface tension (or surface energy). The main difference between surface energy and surface tension is that surface energy measures how much work is required per unit area to stretch, while surface tension measures the force per unit length.
