Soft matter

We usually distinguish three states of matter:

• the gaseous state, of low density, where the atoms (or molecules) are almost independent of each other;

• the liquid state, where atoms (or molecules) are condensed but there is no long-range order;

• the solid state, where atoms (or molecules) are arranged in crystalline lattices.

This classification is not enough to label all the objects around us. In particular, some solid materials have no crystalline order, but are amorphous (glass is a famous example); we may also find that everyday systems such as mayonnaise, shaving cream, gelatin and rubber fall outside the above three categories. The term soft matter has recently been coined to define such systems.