Important Points Regarding Capillarity Action

A substance’s capacity to flow up in a tight tube despite gravity is known as capillary action. It is the consequence of the interaction of two forces: cohesive force and adhesive force. Cohesive force is the attraction between molecules in a liquid, whereas adhesive force is the attraction between molecules in a liquid and molecules on the tube’s surface. The amount of liquid elevated is determined by the container’s diameter and gravitational forces. While water has this unique feature, liquid-like mercury does not since it has a stronger cohesive force than a sticky force.

The Rise of Liquid in a Capillary Tube

A circular capillary tube is dipped vertically in a surface tension liquid. Its meniscus is curved upward as the liquid rises in it. This is the angle of contact between the solid and liquid. The tensional surface force will operate tangentially inward per unit length of the liquid-solid contact line. The force’s direction will produce an angle with the tube wall. The glass wall will feel a force in the direction of the tangent along the line of contact with the liquid. According to Newton’s third law, every action has an equal and opposite response.

As a result, the liquid meniscus faces an equal and opposing force from the glass wall. The response may be broken into two parts: (i) cos vertically up and (ii) sin horizontally outward. The horizontal components cancel out when considering the entire meniscus, whereas the vertical components are added together. 

The entire vertical force supports the column of a liquid standing in the tube on the liquid meniscus. The total vertical force = length of the meniscus force per unit length.

There are a few things you should be aware of:

• Cohesive force: Cohesive force is the force of attraction or repulsion between molecules of the same material. The molecular range is the maximum distance at which molecules may attract one another. If a sphere is thought to be constructed with the molecular range as the radius and the molecule’s position as the centre, the sphere is termed the sphere of influence.
• Adhesive force: Adhesive force is the force of attraction between molecules of different substances. The intermolecular force is 1011 N, whereas the gravitational force is on the order of 1050 N. Intermolecular distances are in the 1010 m range.

The distinction between adhesive and cohesive forces may be remembered by remembering that with adhesive forces, you add another set of molecules, the surface molecules, for the liquid to connect with.

Eotvos Equation for Surface Tension Variation with Temperature

The surface tensions of liquids usually decrease as the temperature rises. Eotvos discovered an empirical relationship between surface tension and temperature. If V is the molar volume and Tc is the critical temperature, the surface tension is calculated as γV2/3 = k(Tc − T), where k is constant for all liquids.

A Few Important Points

1. Capilla is a Latin word that means ‘hair’.
2. Consider it a vertical capillary tube with a circular cross-section (radius a) put into a water vessel open on one side.
3. Water rises in a tight tube against gravity due to a pressure differential across a curved liquid-air contact.

Surface Energy

The structure GBCH consists of two thin wires bent at right angles twice. Another wire AD can glide along BG and CH’s horizontal arms without causing friction. A thin film ABCD will develop in the gap if the framework is immersed in soap solution and removed. 

As a result, surface tensional forces will act perpendicular to and tangential to the film’s surface at every point on the wire AD, and the wire AD will slowly advance towards the framework’s arm BC. To maintain the wire AD in place, an equivalent force in the opposite direction must be applied to maintain the wire AD in place.

Excess Pressure Inside a Spherical Soap Bubble

The bubble is nothing more than air encased in a spherical soap solution coating. The bubble has two surfaces: one on the inside and one outside. Surface tension causes molecules on both sides to feel an inward push. The pressure inside the bubble must be larger than the pressure outside. Otherwise, the bubble would lose its spherical shape.

Conclusion

When one end of a capillary tube is dipped vertically in the water, the liquid rises up the tube until it reaches a point above the vessel’s level. When the same capillary tube is dipped in mercury (or any other non-wetting liquid), the mercury level in the tube falls below the level in the vessel. This leads to a mercury column depression in the tube. Capillarity, or capillary action, is the ascent or fall of liquid in a capillary tube. It causes oil to rise to the top layer of the soil, the wick of a lamp, beneath the water in the soil, and to some extent, in the roots and stems of plants.