Question

The pressure required to prevent liquid from entering a plug of a finely divided solid is twice as great for a liquid of surface tension 50 mN m"1, which completely wets the solid, as it is for a liquid of surface tension 70 mN m"1, which has a finite contact angle with the solid. Calculate this contact angle

Answer 1

We know that

Wetability is inversely proportional to the surface tension

So pressure required will also be incersly proportional to surface tension

Hence surface tension of liquid will be 25 mN - m

Contact angle ,$\cos\theta =\frac{25}{70}=0.3571$

$$\theta =\cos^{-1}=0.3571=69\degree$$