| We discuss general features and physical principles governing the motion of colloidal particles in concentration gradients of a solute. Such situations include both external as well as self-generated gradients. The latter can be used for self-propulsion of a colloidal object as first proposed by Golestanian, Liverpool and Ajdari. Such self-propelling particles are examples of microswimmers which are able to move in a fluid, driven by an active process. The analysis of the physical principles underlying such motion highlights the contraints imposed by momentum conservation on the process. |
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