4.6.3. Surface Tension and Temperature

As the name implies that at the interface of the two fluids or fluid with two liquids or fluid and the gas what it actually happens it if you look at it that way that I have the liquid molecules if you look at this figures okay. I have the liquid molecules and this is the free surface I have the gas. So if I look at what is the intermolecular forces is there, okay like for example if fluid is at rest conditions, the molecules at these points is having the attracting force between the surrounding molecules. There is a same molecules are there so the cohesive force are acting on this. So this cohesive force are making these fluid molecules in moment, moment considerations.

Surface tension occurs at the interface between two different fluids, such as a liquid and gas. At the surface of the liquid, molecules experience forces from all directions except upward, where they encounter air. This results in a net inward force, creating a tension at the surface, which acts like a stretched elastic membrane. These forces can affect the behavior of objects on the surface, like allowing small insects to walk on water.

Imagine a trampoline—when you stand in the middle, the surface stretches downward due to your weight. Just like the trampoline, the surface of water stretches because of the cohesive forces between water molecules, creating surface tension.

As the surface tensions is defined is a force acting per unit length and that is what will be N/m, and the at the surface tension the water with air interference 0.074 N/m at 20oC. And if you look at the molecular perspective view that as the temperature is going to increase it so you will have a decrease of the cohesive forces. As the cohesive forces decreases, you can know if the net force is going to decrease. So resulting effect the surface tensions will have a decreasing trend.

Surface tension is quantified as the force exerted along a line at the liquid's surface, measured in newtons per meter (N/m). For example, water has a surface tension of 0.074 N/m at 20°C. However, as temperature rises, the cohesive forces between liquid molecules weaken, which in turn decreases the surface tension. This means that as liquids warm up, they become less 'sticky' at their surfaces.

Think of a warm bubble bath: as the water heats up, the bubbles can become bigger and more easily pop because the surface tension becomes less strong. Warm water allows for more movement and less 'stickiness' of water molecules, making bubbles less stable.

If you have the surface tension if you can now there will be a net balancing effect of the force component which results us the pressure difference. Let us consider it is the surface tension is given very simple examples of raindrops okay. Any raindrop if you look at that, if you take that drop and make it two splits. At the interface surface there will be surface tension is working it. The surface tension force is acting between the water and the air.

Surface tension can create a pressure difference across the surface of a liquid drop. For example, consider a tiny raindrop; the surface tension exerts an inward force that results in higher pressure inside the droplet compared to the outside atmosphere. This pressure difference is fundamental to the droplet's formation and stability.

Think of a balloon: when you blow air into it, the inflating pressure inside the balloon is higher than the pressure outside. Similarly, in a water droplet, the higher internal pressure provides stability, while the surface tension keeps the droplet intact.

Next interesting point is coming is that if a liquid interfacing with the solids whether it will be wet or not wet, the wetting condition or not wetting condition. That what is a interface between the three of things.

When a liquid meets a solid, its ability to wet the surface depends on the balance of cohesive forces within the liquid and adhesive forces between the liquid and solid. This results in a contact angle: if the angle is less than 90 degrees, the liquid wets the surface; if greater, it does not. This concept is critical in various applications like paint adhesion or inkjet printing.

Consider how water beads up on a waxed car versus how it spreads out on a sponge. This difference in behavior is due to the contact angle—the smooth surface of the wax creates a high contact angle (causing beads), while the porous sponge allows for lower angles (allowing spreading).

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