Question

a)

What are the two important physical quantities that characterize wetting and liquid repellency of a

solid surface? Name them, and explain the difference between these two quantities

b)

Peter is playing around with four different solid surfaces (labelled as A, B, C, and D) by placing

different types of liquids onto these surfaces. Peter found something very puzzling: When he

placed small drops of water and oils onto Surface

A, all of these liquids stick to the surfaces.

However, when he placed water and oils droplets onto Surface B, only water can roll off the

surface but oils remain stuck to the surface. Peter

also

found that both water and oils droplets are

highly mobile o

n Surface C, and can be rolled off from the surface. Finally, when Peter placed

both water and oils droplets onto Surface D,

oil droplets are highly mobile but the water droplets

appear to spread completely on the surface. Please provide possible

physical

explanations to all

the above scenarios. Please remember to include schematics and important physical quantities in

your explanations

Answer 1