Question

The wettability of a surface by a liquid depends primarily on

• A. angle of contact between the surface and the liquid
• B. viscosity
• C. surface tension
• D. density

Answer 1

The Correct Option is A

The wettability of a surface by a liquid is primarily determined by the angle of contact between the surface and the liquid. This concept is described in terms of the contact angle, which is the angle formed at the junction where the liquid, solid, and gas (usually air) phases meet.

• Explanation: The contact angle (\(\theta\)) is a measure of the wettability of a surface by a liquid. It is defined as the angle between the tangent to the liquid surface and the solid surface at the point of contact. This angle is determined by the balance of adhesive and cohesive forces.
• If the angle of contact is less than 90 degrees, the liquid tends to spread, meaning it wets the surface well.
• If the contact angle is greater than 90 degrees, the liquid does not wet the surface well, and it tends to form droplets.

Therefore, the correct answer is the angle of contact between the surface and the liquid. Let's analyze why other options are less relevant in determining wettability:

• Viscosity: Viscosity is a measure of a fluid's resistance to flow and primarily affects the fluid's motion, not wettability.
• Surface Tension: While surface tension is related to the forces at a liquid's surface, it does not directly determine the wettability between a liquid and a solid surface. Instead, it plays a role in the formation of the contact angle.
• Density: Density is unrelated to wettability; it defines the mass of the liquid per unit volume and does not influence how well a liquid spreads over a surface.

Understanding the balance of forces at play at the liquid-solid interface helps in various applications, including coating processes, inkjet printing, and even in nature, like how plants manage water.