Discussion
For a solid/liquid interface the following equation is applicable :
\( \dfrac{\gamma_{SV} - \gamma_{SL}}{\gamma_{LV}} = \mathrm{cos}\,\theta \)
where θ is the contact angle, γSV, γSL and γLV are the surface tension of solid, interfacial tension of S/L and surface tension of liquid.
If a metal pan has to be made non-sticking for cooking appliance :
Answer: C
The pan should be coated with a low energy substance.
From Young's equation, food or water sticks least when it wets the surface least, which means a large contact angle and a small cosθ. That requires a small γSV, a low-energy solid surface. This is why non-stick pans are coated with PTFE (Teflon), whose surface energy is very low.
A high-energy coating would raise γSV and increase wetting and sticking. Surfactants in the water lower γLV and γSL, which improves wetting, the opposite of what is wanted.
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