What are the methods of measuring surface tension?

Surface tension is the property of the surface of a liquid that allows it to resist an external force due to the cohesive nature of its molecules. There are several methods to measure surface tension, and the choice of method depends on the specific properties of the liquid and the precision required. Here are some common methods for measuring surface tension:

Capillary Rise Method:

This method involves measuring the height to which a liquid will rise or fall in a small-diameter capillary tube due to capillary action. Surface tension is related to the capillary rise height through the Young-Laplace equation.
Maximum Bubble Pressure Method:

In this method, a gas bubble is introduced into a liquid. By measuring the pressure required to maintain the bubble at a constant size, surface tension can be calculated using the Young-Laplace equation.
Wilhelmy Plate Method:

A thin flat plate (usually made of glass or metal) is partially immersed in the liquid, and the force required to detach the plate from the liquid's surface is measured. Surface tension can be calculated based on the dimensions of the plate and the force applied.
Drop Weight or Drop Volume Method:

A drop of liquid is allowed to form at the end of a thin tube, and the time it takes for the drop to fall or detach from the tube is measured. Surface tension is related to the drop shape and time of detachment.
Pendant Drop Method:

A droplet of liquid is suspended from the end of a thin tube or needle, and the shape of the droplet is analyzed using optical techniques or image analysis. Surface tension is determined by analyzing the shape of the droplet.
Spinning Drop Method:

A small droplet of the liquid is rotated in another immiscible liquid. The shape of the droplet changes due to the balance of surface tension and gravitational forces. Surface tension is calculated by analyzing the droplet's shape and rotational speed.
Wilhelmy Plate Method:

A thin flat plate (usually made of glass or metal) is partially immersed in the liquid, and the force required to detach the plate from the liquid's surface is measured. Surface tension can be calculated based on the dimensions of the plate and the force applied.
De Nouy Ring Method:

A platinum or stainless steel wire ring is carefully dipped into the liquid and then slowly pulled out. The force required to detach the ring is measured, and surface tension is calculated using the De Nouy equation.
Drop Shape Analysis (DSA):

This modern technique uses high-speed cameras and image analysis software to capture and analyze the shape of a liquid droplet hanging from a needle or a liquid sessile drop on a solid surface. Surface tension is determined from the droplet's geometry.
Each of these methods has its own advantages and limitations, and the choice of method depends on factors such as the nature of the liquid, the available equipment, and the required accuracy of the measurement.