Many of the phases of matter discussed so far, such as gases, liquids, pure solids, solid solutions, liquid crystals, and orientationally disordered crystals, are homogeneous. Both in nature and in the laboratory, materials can be combined to give new materials with different properties. There are important states of matter that are heterogeneous; an Irving Langmuir–Blodgett film is but one example. The film is different from the substrate, making it heterogeneous. Gas, liquid, or solid can be either the dispersed phase or the dispersing medium, and this distinction leads to eight types of colloidal dispersion. However, colloidal dispersions can be kinetically stabilized, and can last for a long time. Some colloidal dispersions can be kinetically stabilized by the presence of surface charges on the dispersed particles; they do not flocculate due to the mutual repulsion between particles. Colloidal microgels have applications in drug delivery, oil recovery, and as viscosity modifiers. Micelles are another heterogeneous phase of matter involving aggregates.