Viscosity and Surface Tension

The properties of viscosity and surface tension are determined by molecular interactions.

Viscosity, on the other hand, is caused by the collaboration of molecules of the same molecules that are found in the same material as one another (in case of fluids).

Contrary to this, surface tension is determined by the difference in interactions between molecules of a fluid and molecules of a substance that is directly in touch with the fluid’s molecules.

What is Surface Tension and how does it work

It is the amount of energy necessary to expand the surface area of a liquid by one unit of area that is known as surface tension. In other words, it is also a feature of the liquid surface that it is resistant to being pushed on. The force that holds the liquid molecules together is intuitively described as maintaining a barrier between foreign materials and the liquid itself.

For example, if we add soap to water, the surface tension of the water reduces, allowing the liquid with soap to more easily combine with the dirt on the hand and so cleaning it. It is also a feature of the liquid surface that it resists being pushed on.

On the surface, it appears to act as a barrier between foreign materials and the liquid. This is the force that binds the liquid molecules together as they form a solid bond.

By adding soap to water, the surface tension reduces, allowing the liquid with soap to more easily mix with the filth on our hands and clean it as a result of the soap.

Surface tension is sometimes expressed as a quantity of energy. More surface tension equals more energy, and therefore fluids take on the shape with the smallest surface area possible in order to reduce energy consumption and maximize efficiency. Water droplets are spherical due to the fact that they have a sphere-like shape. For a given volume, a spherical has the smallest possible surface area.

The definition of viscosity

The viscosity of a fluid is defined as its resistance to flow.

In the case of oil, for example, it has a high viscosity; but, when it is heated in a car, it becomes less viscous and flows more smoothly through the engine and other sections of the automobile. The higher the viscosity of the liquid, the slower the liquid flow will be. With some exceptions, the viscosity of a liquid reduces as the temperature rises.

Viscosity is also referred to as the frictional forces that act between a fluid and the surface with which it comes into contact. The surface can either be a solid surface, such as a pipe, or it can be a fluid surface, such as water. Viscosity is the term used to describe the resistance supplied by the pipe to the water flow. Viscosity, on the other hand, can develop between two fluids that are moving at different speeds.

The phenomena of viscosity described above is extremely specific to liquids, and more specifically Newtonian fluids. While this is true, the interactions between non-Newtonian fluids are quite odd, making them extremely challenging to describe and comprehend.

Surface tension is caused by a variety of factors.

In the presence of cohesive forces, a liquid molecule that is located away from the surface is pulled equally in all directions by neighboring liquid molecules, resulting in a net force equal to zero. The molecules at the surface do not have the identical molecules on all sides of them, and as a result, they are being drawn inside by the surrounding molecules. This results in a small amount of internal pressure and forces liquid surfaces to compress to their smallest possible area.

Because of the cohesive structure of water molecules, there is also a tension parallel to the surface at the liquid-air contact that will resist an external force.

Cohesive forces are those that act between molecules of the same type, whereas adhesive forces are those that act between molecules of different types. Cohesive forces are those that act between molecules of the same type, whereas adhesive forces are those that act between molecules of different types. The degree of wetting, the contact angle, and the shape of the meniscus are all determined by the balance between the cohesion of the liquid and the adhesion of the liquid to the material of the container. At vertical walls, when cohesion dominates (particularly, when adhesion energy is less than half of cohesion energy), the wetting is low and the meniscus is convex, indicating that the meniscus is concave (as for mercury in a glass container). When adhesion predominates (adhesion energy greater than half of cohesion energy), on the other hand, the wetting is high and the corresponding meniscus is concave (as in water in a glass).

The shape of liquid droplets is determined by the surface tension of the liquid. Droplets of water, despite the fact that they are easily distorted, are drawn into a spherical shape by the imbalance in cohesive forces present in the surface layer. Drops of practically all liquids would be approximately spherical if there were no other forces acting upon them. According to Laplace’s law, the spherical shape reduces the amount of “wall tension” that must be applied to the surface layer.

Surface tension’s effects

With ordinary water, a variety of surface tension phenomena can be observed.

Rainwater beading on a waxy surface, such as a leaf. Water clusters into drops because it sticks weakly to wax but strongly to itself. Because a sphere has the smallest possible surface area to volume ratio, surface tension gives them their near-spherical shape.

When a liquid mass is stretched, drop formation happens. The animation (below) depicts water clinging to the faucet and developing mass until the surface tension can no longer keep the drop attached to the faucet. The drop then divides, and surface tension shapes it into a sphere. If there was a stream of water coming out of the faucet, it would break up into drops as it fell. The stream is stretched by gravity, then compressed by surface tension into spheres.

Flotation of nonwettable items denser than water happens when the object’s weight is minimal enough to be supported by surface tension forces. Water striders, for example, use surface tension to walk on a pond’s surface in the following manner. Because there is no connection between the molecules of the water strider’s leg and the molecules of the water, when the leg presses down on the water, the surface tension of the water just seeks to recover its flatness from the leg’s distortion. The water’s action pulls the water strider upward, allowing it to stand on the water’s surface as long as its mass is small enough for the water to support it. The water’s surface behaves like an elastic film: the insect’s feet make indentations in the surface, increasing the water’s surface area, while the water’s inclination to minimise surface curvature (so area) pushes the insect’s feet higher.

A strain at the surface between dissimilar liquids causes separation of oil and water (in this case, water and liquid wax). The term “interface tension” is used to describe this form of surface tension, but the chemistry is the same.

Conclusions 

Molecular interactions control viscosity and surface tension.

However, viscosity is caused by molecules working together in the same medium (in case of fluids).

Surface tension is determined by the difference of interactions between the substance (fluid) molecules in contact.

Surface tension is the energy required to raise the liquid’s surface area. In other words, the liquid surface resists force. Intuitively, it keeps external objects out of the liquid and keeps the liquid molecules together.

Viscosity is sometimes regarded as frictional forces between fluid and contact surface. The surface can be solid, like a pipe, and the fluid can be water. The pipe’s barrier to water flow is now viscosity. However, viscosity can occur between two fluids moving at varying speeds.