Surface Tension

Water striders are small insects in the water that can walk on the water surface without getting submerged. This is due to their extremely less weight on the water surface. This depends on the solid, liquid, or gas in contact, which are basically the forces of attraction. It is also dependent on the particles within the liquid. The liquid’s surface acts as an elastic sheet.

Surface tension is a feature of liquids that is influenced by intermolecular interactions and is derived from the cohesive forces that exist between molecules in a liquid. According to thermodynamics, systems like paints and inks attempt to achieve a state with the greatest number of beneficial interactions. This means that liquids will take on a structure in which the number of bulk molecules is maximised and the number of surface molecules is minimised.

Surface molecules are partially naked since they are not completely surrounded by their peers at the liquid’s surface. When compared to molecules in the bulk of the liquid, molecules near the liquid-air interface have less favourable interactions and are in a higher energy state. As a result, energy is required to transfer molecules from the liquid’s bulk to the surface. The more energy it takes to expand a liquid’s surface area, the stronger the interactions between the molecules.

The surface tension of water

The International Association for the Properties of Water and Steam (IAPWS) has calculated the surface tension of pure liquid water in contact with its vapour as:

Yw = 235.8 (1-T/TC)1.256[1-0.625 (1-T/TC)]mN/m,

Temperature T and the critical temperature TC = 647.096 K are both given in kelvins. From the triple point (0.01 °C) through the critical point, the complete vapour-liquid saturation curve is valid.

Surface tension examples

• Walking on water: Because their weight is insufficient to penetrate the surface, little insects like the water strider may walk on water.
• Floating a needle: Even though it is several times as dense as water, a precisely placed little needle may be made to float on the surface of the water. The needle will descend quickly if the surface is disturbed to break up the surface tension.
• Don’t get your hands on the tent! : The surface tension of water will bridge the pores of finely woven tent fabrics, making them slightly rainproof. However, if you press your finger on the tent material, the surface tension is broken, and rain will trickle through.

The effect of temperature on surface tension

Surface tension is a feature of liquids that causes them to operate as a stretchy membrane. Surface tension is caused by the attraction of molecules in all directions, causing the liquid’s outermost layer to operate as an elastic membrane. Because surface tension is determined by the intermolecular forces between liquid molecules, as the temperature rises, the molecules gain more energy and become more active, moving randomly. As the temperature rises, the molecule becomes more unstable, reducing the strength of the liquid’s outermost membrane. Thus, the surface tension decreases.

Unit of Surface Tension

Unit of Surface Tension is the Newton per Metre or it can be written as the N/m .

• SI unit = N/m
• And the CGS unit = dvm/cm 

Dimension of Surface Tension

Since we have the knowledge that the formula for surface tension can be written as, 

So, surface tension = F/L

The F is equal to = ma,

Now by putting the value of F into F/L we get, 

ma/L

When into the equation the fundamental quantities are equated, we get,  

we get = MLT-²L-¹

Now, when we solve the equation, we finally get,

we get =MT-²

Therefore, the surface tension dimensional formula can be written as MT-²

For Calculating Surface tension.

With the help of an example, we are going to calculate the surface tension by using its formula, 

For calculating the given liquid’s surface tension whose dragging force is = 7 N

And in which the force acts, the length is = 2 m. 

The Solution, 

So, the given values are, 

F = 7 N, and L = 2 m

The formula of surface tension is, T = F/L

Now, by putting the value of the equation we get, 

⇒ The surface tension (T) = 7/2

⇒ The surface tension (T) = 3.5 N/m

Therefore, the surface tension for the above-mentioned question is = 3.5 N/m

Some Methods of Measurement of the surface tension.

There are many methods for measuring the Surface tension, some of the methods are mentioned below, 

• We can measure the surface tension with the Spinning drop method.
• We can measure the surface tension with the Du Noüy–Paddy method.
• We can measure the surface tension with the During method.
• We can measure the surface tension with the Pendant drop method. 
• We can measure the surface tension with the Capillary rise method
• We can measure the surface tension with the Stalagmometric method.
• We can measure the surface tension with the Bubble pressure method. 
• We can measure the surface tension with the hemispherical liquid drop and the oscillation of a spherical method.
• We can measure the surface tension with the vibrational frequency of the levitated drops method.
• We can measure the surface tension with the Sessile drop method.

Conclusion:

Surface tension is the phenomenon that arises when the surface of a liquid is in touch with another phase, it is explained as per the definition of surface tension. The Van der Waals force is an intermolecular force that mainly brings out the liquid particles together. Towards the rest of the liquid, the particles are pulled, along with the surface. The length L with the force acts from the ratio of the surface force F. The SI unit of Surface Tension. The surface tension of water will link the pores in the tent material from the rainproof ten material. The surface tension also holds accountability for the shape of liquid droplets. We can measure the surface tension with the Bubble pressure method.