Surface energy (E) = Energy × [Area]-1 . . . ( 1) Since, Energy = Force × displacement = m × a × displacement. Or, Energy = [M1 × M0 L1 T-2 × L1] Therefore, the dimensional formula of energy = [M1 L2 T-2] . . . (

As the planar density increases, the number of nearest atoms in the plane increases, which results in an increase in the number of satisfied atomic bonds in the plane, and a decrease in the number of unsatisfied bonds. (That is, surface energy decreases with an increase in planar density.)

As we know that the potential energy of a molecule on the surface of liquid is higher than that inside a liquid, there is some energy required to form the surface. This energy is known as the surface energy for that liquid. Surface energy per unit area is known as the surface energy density.

Surface energy quantifies the disruption of intermolecular bonds that occurs when a surface is created. It is also called as surface free energy or interfacial free energy. In simple language, surface energy can be defined as the work per unit area done by the force that creates the new surface.

Surface energy is a term used to describe the excess interaction energy that exists at the surface of a given substrate. A high surface energy (HSE) means a strong molecular attraction, therefore easier to bond, whereas a low surface energy (LSE) means a weak molecular attraction, therefore harder to bond.

Surface energy can be defined as the energy required per unit area to increase the size of the surface, and as such is often quoted in units of mN/m. Surface tension of the liquid will also play a role, as will the type of interactions between the liquid and solid.

The attractive force of the molecules present at the surface of a liquid towards each other is called the surface tension of that liquid. Surface energy is the equivalent attractive force present between the molecules at the surface of a solid substance.

Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.

Critical Surface Tension. The critical surface tension of a solid surface is an indication of its relative water-hating or water-loving character. A low critical surface tension means that the surface has a low energy per unit area. The quantity is based on experiments with a series of pure liquids.

Wettability is the ability of a liquid to maintain contact with a solid surface, and it is controlled by the balance between the intermolecular interactions of adhesive type (liquid to surface) and cohesive type (liquid to liquid).

Such “polymer brushes” allow researchers to control surface properties such as friction or interactions with water. Adding these kinds of particles can change the properties of the liquid, making it anticorrosive, for example.

Wettability can be measured through contact angle When the contact angle is above 90° the wettability is bad, when it is below 90° the wettability is good. When water is used as a measuring liquid, the surface is called hydrophobic when the contact angle is above 90° and hydrophilic when it is below the same value.

Wettability of a solid surface is commonly measured with an optical tensiometer by utilizing the sessile drop method. A water droplet is placed on the surface and the formed contact angle is measured from the three-phase boundary where liquid, gas and solid intersect.

Here is an example of calculating surface tension by using the formula.

1. Compute the surface tension of a given liquid whose dragging force is 7 N and length in which the force acts is 2 m?
2. Solution:
3. T = F/L.
4. ⇒ T = 7/2.
5. ⇒ T = 3.5 N/m.

Calculate the contact angle For example, if the gradient is 3, then you can use the relationship tan(θ) = (opposite/adjacent) = (3/1) to calculate the angle. Once you have the baseline and the droplet edge, you can calculate the angle between them.

The effect of surface tension on capillary pressure is more complicated: on one hand, the capillary pressure is directly proportional to the surface tension. On the other hand, high surface tension liquids typically also have higher contact angles, which lower the capillary pressure.

The angle of contact depends upon the liquid’s nature and the solid in contact and the medium which exists above the free surface of the liquid.

Contact angle is a measure of wettability Water contact angle will immediately give an indication of the wettability of the solid. If the measured contact angle is above 90 degrees, the solid is said to have poor wetting and is termed hydrophobic. If the contact angle is below 90 degrees, a term hydrophilic is used.

When an interface exists between a liquid and a solid, the angle between the surface of the liquid and the outline of the contact surface is described as the contact angle θ (lower case theta). The contact angle (wetting angle) is a measure of the wettability of a solid by a liquid.

When the liquid surface is curved concave upwards, the angle of contact is acute and when the liquid surface is curved convex upwards, the angle of contact is obtuse. Characteristics of the Angle of Contact: The angle of contact is constant for a given liquid-solid pair.

For pure water and perfectly clean glass, the angle of contact is 0°. For ordinary water and glass, it lies between 8° and 18°. For pure water and pure silver, the angle of contact is 90°. When pure water is put in pure silver vessel, the surface of water is flat.

Baneroft. s) The mercury-glass contact angle is of the order of 140~ 9 Using this value in equation 4, we get ~ = 0.12. Therefore, when a drop of mercury is plaeed on a glass plate, one-eighth of the ” Apparent solid- liquid interfaee” represents actual contact between the mercury and the glass.

When the angle of contact is between the solid and liquid is 900, cohesive force is equal to adhesive force because they will be in equilibrium state and we will get the flat meniscus in this case.

convex

If θ is obtuse, i.e; θ >90°, then liquid meniscus will be convex upwards. If angle of contact is acute angle, i.e; θ <90°, then liquid will wet the surface.

What does the high surface tension do to the number of liquid molecules that can stay together? It keeps the liquid molecules together, The higher the surface tension the more molecules stay on. The water had the highest surface tension and the soapy water had the lowest surface tension.