Final answer:
Repression of the double layer involves neutralizing the charged layer of a colloid particle, leading to its destabilization and subsequent aggregation and precipitation. When opposite-charged ions from the surrounding medium interact with the colloidal particles, they can cancel out the charge, causing the particles to clump together and settle out of the solution.
Step-by-step explanation:
Repression of the double layer refers to the process that leads to the destabilization of colloidal systems. In colloids, particles are surrounded by an outer charged layer, often achieved through the adsorption of ions from a surrounding medium to their surfaces. This creates a double layer with the colloid particle itself and the adsorbed ions with the opposite charge. When this layer is neutralized by ions with an opposite charge from the surrounding medium, the colloidal stability is compromised, leading to aggregation and precipitation of the particles.
For example, in inland waterways, positively charged clay particles form a stable colloidal suspension. However, when this suspension flows into the sea, the high concentrations of salts in seawater can supply ions that neutralize the charge on these clay particles. As a result, the repulsion between particles is reduced, and they can come together to precipitate, leading to the formation of new land at the mouths of rivers, as observed in the Mississippi River delta. This phenomenon is an application of charge neutralization which has practical importance in environmental engineering, such as in reducing particulate emissions from power plants.