# Is the surface tension of a liquid droplet stable?

• lionelwang
In summary, the surface tension for water is typically 72mN/m at RT, but this value may be lower due to surface contamination, surfactants, or other solutes. The curvature of a droplet can vary and can support spatial gradients, such as Marangoni flow, if there is a temperature or concentration gradient. This does not change the interfacial energy, which remains a property of the two phases.
lionelwang
Hi all,

Typically, we know that the surface tension for water is about 72mN/m at RT. so do this mean that the surface tension over the whole droplet is exactly the same? Moreover, we know that the Laplace pressure may be different over the whole droplet as the curvature in different parts might be different. How to explain those phenomena?
Waits for your wisdom, and thanks for any help!

the value you quote is for pure water- surface contamination, surfactants, or other solutes will drastically lower the value.

The curvature is allowed to vary with, for example, height in a gravitational field (hydrostatic pressure head). This does not change the interfacial energy, which is a property of the two phases.

The interfacial energy can support spatial gradients (Marangoni flow, for example) if there is a temperature or concentration gradient.

does that help?

## 1. What is surface tension and how does it affect the stability of a liquid droplet?

Surface tension is the force that causes the molecules on the surface of a liquid to stick together. It is responsible for the shape and behavior of liquid droplets. The higher the surface tension, the more stable the droplet will be.

## 2. How does the size of a liquid droplet affect its surface tension and stability?

The smaller the droplet, the higher the surface tension. This is because there is a higher ratio of molecules on the surface compared to the volume of the droplet. As a result, smaller droplets tend to be more stable than larger droplets.

## 3. Can the surface tension of a liquid droplet be manipulated?

Yes, the surface tension of a liquid droplet can be manipulated by adding certain substances, such as surfactants, which can decrease the surface tension. This can make the droplet less stable and more likely to break apart into smaller droplets.

## 4. How does gravity affect the stability of a liquid droplet?

Gravity plays a significant role in the stability of a liquid droplet. It pulls down on the droplet, causing it to spread out and flatten. This can decrease the surface tension and make the droplet less stable. However, if the droplet is small enough, the surface tension can overcome the force of gravity and keep the droplet intact.

## 5. What factors can cause the surface tension of a liquid droplet to change?

The surface tension of a liquid droplet can change due to temperature, the presence of other substances, and the size of the droplet. It can also be affected by external forces such as gravity, air currents, and vibrations. All of these factors can alter the stability of a liquid droplet.

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