Surface Energy

The breaking of intermolecular connections that happens when a surface is formed is quantified by interfacial free energy or surface energy. Surfaces must be axiomatically less energetically favourable than the bulk of the material (the molecules which appear on the surface possess greater energy in comparison to the molecules present in the bulk of material)in solid physics; otherwise, there would be a driving force for surfaces to be produced, reducing the mass of the substance. As a result, surface energy may be interpreted as either the excess energy at a material’s surface relative to the bulk, or it can be described as the effort necessary to produce an area of a specific surface. Another approach to look at surface energy is to compare it to the amount of work necessary to cut a bulk sample into two surfaces. There is “extra energy” as a result of the now-incomplete, unmet link between the two surfaces.

When we stretch a spring, we state that some work is done on it, and that work is retained in the form of Potential energy referred to as Elastic potential energy. There will be no potential energy if the body is in its austenitic state. Likewise, when we talk about free surfaces of liquids, we know that the free surfaces of liquids are considered to be stretched membranes, so the surface will retain some potential energy due to the stretched surface, which is referred to as Surface energy or Surface free energy because it is only at the liquid’s surface.

When a solid body is cut into fragments, its interactions are disrupted, increasing surface area and hence surface energy. If the cutting is done transiently, the energy utilised by the cutting process will be equal to the energy implicit in the two new surfaces created. All other factors being equal, the unit surface energy of a material would therefore be the energy of cohesion; in actuality, this is true only for a freshly created vacuum surface. Surfaces frequently deviate from the basic “cleaved bond” concept described above. They are discovered to be highly dynamic zones that easily reorganise or react, resulting in energy reduction via processes like passivation or adsorption.

Difference between Surface Tension and Surface Energy: 

Surface tension and surface energy are measures of the intermolecular forces that make up a substance. Because of these intermolecular interactions, a liquid’s surface is continually being drawn inward. Work should be done to offset intermolecular forces when extending the surface. The surface tension and surface energy of a liquid may be measured, as can the time and energy necessary to extend that surface. The primary distinction between surface energy and surface tension is that surface energy is used to calculate the amount of labour necessary to stretch a surface per unit area, whereas surface tension is used to calculate force per unit length of the surface.

High Surface Energy

There is a difference in the surface energy which ranges from higher to low level. It depends on the chemical composition. Surface molecules are so strongly attracted to one another that they will happily be persuaded to liquid molecules as well. As a result, these materials are quite simple to wet out and bind. Many metals and glasses have surface energies on the order of 100s or 1000s of dynes/cm, making them high surface energy materials.

High surface energy is essential for solution wetting, particularly in procedures such as spin coating. When exposed to air conditions, most solids with high surface energy will lose their high-energy surface. Hydrocarbon impurities in the air will adsorb on the surface of the solid, lowering the surface energy. Surface treatment, which is often aimed to boost the energy by removing impurities or generating high surface energy functional groups, is the most frequent way of adjusting surface energy. Many of these strategies only create short-term changes in surface energy. This is due to the fact that adsorption of low surface energy molecules occurs gradually over time, lowering the average surface energy.

Surface energy formula 

Surface energy is mathematically represented as- 

Surface energy = Work Done/Area .joule/m2

Therefore, the SI unit of surface energy is newton/metre or joules/m².  

Example – Let the surface tension of water be 72 10-³ N/m, and the length of the two parallel lines be 20 cm each. If the separation between the two parallel wires is 1cm, then what is the work required to increase the surface area by 2mm. 

Solution – From the statement mentioned above, we can gather the following information- 

The length of the two wires is 20 cm each. 

The separation between the two wires is 1cm = 10-² m 10–³ m. 

The surface tension of the water = 72 10-³

Increase in the surface area = 2mm = 2  

As we have established in an earlier segment, increase in surface energy = T increase in the surface area. 

Increase in surface area = 2x 20x 2x 10–³ = 80 × 10-³ m2 

Increase in surface energy = (72 10-³) (80 × 10-³) = 5.76 10-³ J 

Therefore, the required work to be done is 5.75mJ in order to increase the surface area by 2mm.

Conclusion:

The extra energy of the surface, as opposed to the volume of the material, is referred to as the surface energy. It describes how a solid body behaves when immersed in a liquid medium. As a result, it aids in assessing the adhesion between the two states, solid and liquid. If the surface area is tiny, the liquid surface will exert a lot of surface energy (Ex: Oxides, Metals, Ceramics). The energy exerted by the surface is reduced if its area is large.  Low surface energy materials are materials that have low surface energy.