Why does a damp sponge work better to mop up a spill than a dry one?

Question

I would expect that a dry one would have more capacity to absorb the spill, but it just pushes it around.

In: 1

Answer 1

With a dry sponge, you’re trying to get the liquid to “stick” to the sponge through adhesion (liquid-solid interaction). With a wetted sponge, the water has already adhered to a lot of the sponge surface. What happens instead is that the spill liquid mixes with the water that’s already on the surface; liquid-liquid mixing is pretty fast, so this happens quickly. The mixed liquid is physically “held” by the property of cohesion, which is a liquid’s attraction/stickiness to itself.

So you’re trading the slow process of adhesion of the spill liquid for the faster process of liquid-liquid mixing and cohesion.