Question

Consider the following diagram where an oil droplet is formed on a fabric immersed in water. At equilibrium, the balance of various interfacial forces acting on the droplet is given by the following equation:
$\gamma_{FW} = \gamma_{FO} + \gamma_{OW} \cos \theta$
When a surfactant is added to water, assuming that $\gamma_{OW}$ and $\gamma_{FO}$ remain unchanged, the following happens:

• A. $\gamma_{FW}$ decreases and the oil droplet tends to become rounder
• B. $\gamma_{FW}$ increases and the oil droplet tends to become flatter
• C. $\gamma_{FW}$ decreases and the oil droplet tends to become flatter
• D. $\gamma_{FW}$ increases and the oil droplet tends to become rounder

Answer 1

Answer: (A)

$\gamma_{FW}$ decreases and the oil droplet tends to become rounder

Answer 2

The correct option is (A): $\gamma_{FW}$ decreases and the oil droplet tends to become rounder