One of the ways to describe surface tension in fluids is: the property of a liquid’s surface that resists force. It serves as a barrier to foreign materials and holds the liquid together. This ever-present property is caused by unbalanced forces on surface molecules that pull toward the main part of the liquid.

What are some of the primary conditions that affect surface tension? The surface tension characteristics of a fluidic substance stay basically stable,📷 but can be changed by temperature variations, chemicals that modify the bonding characteristics of the molecules, oxidation and the presence of impurities. Let’s consider the effects of these four conditions on surface tension:

Temperature

As temperature decreases, surface tension increases. Conversely,  as surface tension decreases strong; as molecules become more active with an increase in temperature becoming zero at its boiling point and vanishing at critical temperature.

Chemical Additions

📷Adding chemicals to a liquid will change its surface tension characteristics. The effect of adding an unrelated chemical to a substance, and thereby changing its surface tension, is demonstrated by the example of putting soap (a surfactant) in water to reduce the surface tension, which allows the dirt on your hands to more easily mix with the water.

Oxidation

Oxidation directly affects surface tension. As surface tension increases, intermolecular forces increase. Oxygen in the atmosphere is known to decrease the surface tension of various substances.  The Presence of ImpuritiesThe presence of impurities on the surface of, or dissolved in, a substance directly affects the surface tension of the liquid. The surface tension of water, for example, will increase when highly soluble impurities are added to it.

Surfactant

Now that we've considered the effects of variation in temperature, the addition of chemicals, oxidation, and the presence of impurities on surface tension, maybe we should next consider the effect of a surfactant over time and how we observe and measure this effect.

The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m–1) than under equilibrium conditions (∼72 mN m–1) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments

Article The Dynamic Surface Tension of Water

Surface Tension: "The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules."

The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface of a glass of water do not have other water molecules on all sides of them and consequently they cohere more strongly to those directly associated with them (in this case, next to and below them, but not above). It is not really true that a "skin" forms on the water surface; the stronger cohesion between the water molecules as opposed to the attraction of the water molecules to the air makes it more difficult to move an object through the surface than to move it when it is completely submersed

As surface tension increases, inter-molecular forces increase. ... The surface tension of water, for example, will increase when highly soluble impurities are added to it.

When detergent is added to water, it decreases the surface tension of the water. Compounds that lower water's surface tension are called surfactants, which work by separating the water molecules from one another.

Soaps and detergents: These help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas. Washing with cold water: The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent

Adding salt to water does increase the surface tension of water, although not by any significant amount. ... However, experiments done with salt water show that surface tension actually increases when salt is added to pure water.

It has been reported in the literature that sugars such as dextrose and sucrose increase the surface tension of water. The effect was interpreted as a depletion of the solute molecules from the water-air interface. ... The surface tension decreases continuously with increasing concentration

The increase in interfacial tension with increasing brine salinity from 40,000 to 200,000 ppm NaCl is due to that, the positive charge of sodium (Na+) attracts to the negative charge of the polar moiety (hydrofoil) and consequently decreases the solubility of oleic acid in water.

After noting the density of each liquid it became clear that the higher the density the greater the surface tension. The experiment showed that water, the liquid with the highest density, has the highest surface tension; while alcohol,the liquid with the lowest density, has the lowest surface tension

How does temperature influence surface tension? In general, surface tension decreases when temperature increases because cohesive forces decrease with an increase of molecular thermal activity. The influence of the surrounding environment is due to the adhesive action liquid molecules have at the interface

Does surface tension increase with surface area?

Surface tension is the energy, or work, required to increase the surface area of a liquid due to intermolecular forces. Since these intermolecular forces vary depending on the nature of the liquid (e.g. water vs. Water droplets form on the surface of the water pool because of surface tension

Does surface tension change with pressure?

A decrease in surface tension with increasing pressure is, however, due to more similar densities between these dissimilar constituents. Related to this, it is found that the slope of surface tension with temperature itself decreases at higher pressures.

Does the surface tension of water change (increase/decrease), as the surface area changes?

If you use a standard surface tension measuring device to measure the surface tension of water in a pail or in a lake you'll get the same measurement (assuming the same water composition and temperature). So, the surface tension of water is independent of the area of the water body.

But maybe you refer to the case of a film of liquid stretched within a wire frame (as is commonly used to illustrate the concepts of surface tension and surface energy)

All details about surface tension via Science direct here

https://www.sciencedirect.com/topics/materials-science/surface-tension

Gamal B. Abdelaziz - Thank you for your swift response and link to the paper. From what I gather, the addition of salt increases the surface tension of water however is there a value in terms of N/m for comparison with pure DI water(72.8 dynes/cm). Thank you.

The water molecules attract one another due to the water's polar property. The hydrogen ends, which are positive in comparison to the negative ends of the oxygen cause water to "stick" together. This is why there is surface tension and takes a certain amount of energy to break these intermolecular bonds. Same goes for other liquids, even hydrophobic liquids such as oil. There are forces between the liquid such as Van der Waals forces that are responsible for the intermolecular forces found within the liquid. It will then take a certain amount of energy to break these forces, and the surface tension. Water is one liquid known to have a very high surface tension value and is difficult to overcome.

This is a very good link

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/States_of_Matter/Properties_of_Liquids/Surface_Tension

Please read this document:

http://www.youngscientist.com.au/wp-content/uploads/2016/01/216-report.pdf

Good document Dhinakaran Veeman

Please, tell me about the surrounding gas and the material of the substrate.

Possibly by reducing the temperature. Or we can go for additives such as glycol if it chemically satisfies the situation we are dealing with.

Dear Ajith Krishnan Rohini

Yes. Decreasing temperature and Addition of surface tension decreasing materials is solutions of the problem

A molecule at the surface of a liquid experiences net inward cohesive forces. Usually, we try to reduce those forces in water so it can wet surfaces more easily. Water does not wet waxed surfaces because the cohesive forces within the drops are stronger than the adhesive forces between the drops and the wax.

most inorganic solutes increase the surface tension of water. Another source suggests that surface tension could be increased if you increase the polarity of water by adding a more polar substance. But there seems to be contradictory evidence both NaOH and Na2S2O3 decrease the surface tension of water. And there is an article (given DOI) that shows 8 M NaCl to have a surface tension of about 85 dyne/cm. So it would seem that if there is an effect, it is small.

DOI: 10.5194/acp-2017-1013

Dear Saumya Gulati just in case that this question is still of interest to you: Please have a look at the following useful link

Chemicals to increase the surface tension of water

https://chemistry.stackexchange.com/questions/134390/chemicals-to-increase-surface-tension-of-water