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Surface Tension in Silicone Oil | High & Low Impacts & Applications

April 29, 2025

We often say that a certain liquid has “high surface tension” or “low surface tension”, but what exactly does this mean? Is it merely a change in the value of a physical parameter, or will it have a fundamental impact on the behavior of the liquid, experimental methods, and even daily life?


Surface Tension in Silicone Oil | High & Low Impacts & ApplicationsSurface Tension in Silicone Oil | High & Low Impacts & Applications

The answer is yes. Surface tension not only determines the shape and flow pattern of a liquid, but also influences various natural phenomena and engineering operations. This article will start from the definition of "surface tension", explore the specific differences brought about by its high or low value, and illustrate why it is so important by combining several typical cases.



I. What is Surface Tension?

Surface tension is the ability of the molecules on the liquid surface to contract the surface area and resist external disturbances. Its essence stems from the unbalanced cohesive force experienced by the liquid surface molecules: molecules inside the liquid are evenly surrounded by neighboring molecules, while surface molecules lack the upward attractive force, thus contracting inward, creating an effect similar to a “taut film”.
The unit of surface tension is N/m, and there are significant differences among different liquids. For example, at room temperature:


  • The surface tension of water is approximately 72.8 mN/m.

  • That of ethanol is about 22.3 mN/m.

  • And that of mercury is as high as approximately 485.5 mN/m.
    It is precisely these numerical differences that lead to significant variations in the physical behavior and practical applications of liquids.

II. What are the Characteristics of Liquids with High Surface Tension?

Liquids with high surface tension usually exhibit stronger contraction and anti - deformation abilities. The specific impacts include:


  1. Droplets are closer to spherical shape
    The higher the surface tension, the more droplets tend to contract into a spherical shape to minimize the surface area. At a microscopic scale where gravity has no effect, high - tension liquids almost always take on a spherical shape, such as water droplets or mercury droplets in space.

  2. Difficult to wet other surfaces
    For example, mercury does not spread on the glass surface but remains in a bead - like form. This is because the surface tension of mercury is much greater than the adhesive force between it and the glass, causing it to “cluster together” rather than “spread out”.

  3. Strong anti - evaporation and anti - penetration abilities
    Liquids with high surface tension are less likely to penetrate through porous media and are more difficult to evaporate quickly, which has unique advantages in certain sealed systems.

III. What are the Manifestations of Liquids with Low Surface Tension?

Liquids with low surface tension are easy to spread and deform, and have a strong affinity for surfaces. Their common manifestations are:


  1. Easy to wet
    Liquids like alcohol, acetone, and detergent water can quickly spread on surfaces such as glass and metal, indicating that their interfacial energy is low and the intermolecular forces are weak.

  2. Suitable as penetrants or lubricants
    Low surface tension helps liquids penetrate into micropores or capillary structures, so they are commonly used in fields such as cleaning agents, wetting agents, and printing inks.

  3. Poor droplet stability
    Low surface tension reduces the overall stability of droplets, making them prone to rupture or diffusion. Therefore, in systems such as emulsions and foams, surfactants are often added to regulate the tension.

IV. Analysis of Typical Application Cases

Case 1: Why is mercury used instead of water in the mercury intrusion porosimetry experiment?
Mercury intrusion porosimetry is commonly used to determine the pore structure of materials such as coal, ceramics, and catalysts. The principle is to gradually increase the external pressure to make the liquid penetrate into the solid micropores, thereby analyzing the pore size distribution.
Mercury is chosen as the intrusion liquid instead of water mainly for two reasons:


  • Mercury has an extremely high surface tension (about 485.5 mN/m), which means it is not easy to penetrate into micropores and will only be “pushed” in under high pressure, helping to distinguish the intrusion pressures of different pore sizes.

  • Mercury does not wet most solids, which can prevent the liquid from naturally diffusing into the pores, thus obtaining more accurate physical pore size data.
    If water with a relatively low surface tension is used instead, it will automatically wet the pores and penetrate in without the need for external pressure, completely ruining the purpose of the experiment.


Case 2: The “Lotus - leaf Effect” where raindrops form beads on lotus leaves
The surface of lotus leaves has a micro - nano dual - scale hydrophobic structure, which prevents water droplets from spreading. In this case, the relatively high surface tension of water causes the droplets to contract into spheres, reducing the contact area with the lotus leaf surface and achieving “self - cleaning by rolling beads”. This is the famous “Lotus - leaf Effect”.
Conversely, if alcohol is dropped on the lotus leaf, it will spread immediately and lose its self - cleaning ability, mainly due to its low surface tension.


Case 3: Inkjet printing and ink control
In inkjet printing, the surface tension of the ink must be strictly controlled. If the tension is too high, droplets are difficult to separate from the nozzle; if the tension is too low, the ink droplets will spread excessively on the paper, resulting in a blurred image. Therefore, surfactants are often added to the ink to “adjust the tension” to achieve the best balance of smooth droplet formation and clear images.


Case 4: Why add soap when making soap bubbles?
The surface tension of pure water is too high to be easily stretched into bubbles. Soap molecules can reduce the surface tension of water, making the liquid film easier to expand and stabilize, forming colorful soap bubbles. This is a classic application of surfactants reducing tension and stabilizing the interface.

V. Summary: The Magnitude of Tension Has No Superiority or Inferiority, and the Key Lies in the Application Scenario

The magnitude of surface tension does not represent the “goodness” or “badness” of a liquid, but rather their ways of performance under different functional requirements:


  • High - tension liquids are used for structure control and pore analysis.

  • Low - tension liquids are suitable for wetting, diffusion, and cleaning.

  • Surfactants establish a “controllable balance” between the two by adjusting the tension.
    Understanding and utilizing surface tension is an important foundation in fields such as material design, liquid manipulation, microfluidics, and interfacial chemistry.


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