Colloidal suspensions are comprised of microscale particles dispersed in a solvent. We use colloids every day, including in paints, aerosols and milk, making their study of great practical value. Yet they also represent a rich source of experimental model systems, as the Brownian motion of colloidal particles is analogous to the thermal motion of atomic systems, but their characteristic size allows for detailed study using simple optical microscopy and even manipulation at the single particle level by external fields. When combined with the possibility of extensive tunability with respect to their shape and surface chemistry, this allows for a vast range of systems to be mimicked. 
Colloidal models, for example, offer the opportunity to study the physics of condensed matter systems with the very simplest interactions – hard spheres– up to those with particles that exhibit the specific and directional bonding required for the self-assembly of colloidal molecules.
Understanding membrane transport