Consider a bowl filled with water on which some black pepper powder have been sprinkled uniformly. Now a drop of liquid soap is added at the center of the surface of water. The picture of the surface immediately after this will look like.

The water surface exerts a surface tension. When the pepper powder is sprinkled uniformly on the water surface, the powder particles remain at their position. But as soon as a drop of liquid soap is added at the center of water surface, surface tension of water breaks at the center, so the remaining part of water exerts a net surface tension outwards and the water spreads outwards taking the powder particles outwards along with it as shown in the figure C.