Colloids are a class of material that is relevant in the whole daily life: food (milk), cosmetics (shaving cream), weather (fog), pharmacy (paste), chemistry (paints) , biology (blood), materials (compounds) etc. In particular colloidal dispersions are mixtures of two or more substances on a mesoscopic scale – e.g solid particles (dispersed phase) which are homogeneously distributed in a liquid (dispersion medium).
One important property defining colloidal dispersions is the size range of the dispersed phase consisting of particles smaller in a size range of about 10nm - 10 µm. Colloidal systems are an important part of the field of soft condensed matter physics. ‘Soft’ because the elastic moduli of soft matter (e.g. gel) are about 1010 times smaller than compared to hard matter (e.g. iron). They are soft although the interaction between the colloidal particles is of the same order as between atoms in the solid state. The reason is that the inter particle distance in colloids is about 103 larger than in atomic systems.