Depletion interactions

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Definition

Depletion interactions.
As the colloidal particles in the solution come together (yellow), the polymer bundles (green) are excluded from the depletion zone. (Image from http://bit.ly/1pHFHN)

Depletion interactions occur when a solution contains particles that have a size or length scale between that of the other suspended particles and the solvent molecules in a solution. These intermediately sized particles could be for example polymers (dissolved and not absorb onto the surface of the other particles). Depletion interactions are due to osmotic pressure and are attractive interactions. As colloidal particles come together in a solution, the polymer bundles are pushed away and excluded from the "depletion zone" between the particles. The solution will then become unbalanced and the other colloidal particles will continue to attract.

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