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Why does a slightly damp sponge absorb water so much better than the same sponge when it is bone dry?
Chris Daniel
Colwyn Bay, Conwy, UK
Sponges for dish washing can be made of polyester, which has mechanical properties that make it useful as a cleaning material, as well as being soft to handle when dry or wet. However, the polymer is hydrophobic, or water-repellent, which means its surface energy is lower than the surface energy, or surface tension, of water.
A dry sponge will therefore tend to float when placed on water, only absorbing liquid gradually. It can…
