Branch of Physics dealing with physical properties of colloidal systems (i.e. motion, forces, etc. at the scale of the colloidal system).
The branch of soft matter dealing with colloids has a close connection with the other subjects of Condensed matter physics, like Solid-state physics. This is because colloidal Suspensions in many ways can behave analogously to solids, whether crystalline or glassy. Colloidal particles have also been used as model systems for atoms or molecules, and so there are some connections with Atomic physics and Molecular physics.
These are important in Active matter (see Active colloid), in Biophysics, and Nanotechnology.