Soft matter

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Soft matter comprises a variety of states, perhaps best distinguished as being dominated by energies of the order of room temperature thermal energy. At these temperatures, quantum aspects are generally unimportant. Pierre-Gilles de Gennes received the Nobel Prize in physics in 1991 for his research on soft matter.

Soft matter substances have a wide range of applications, such as structural and packaging materials, foams and adhesives, detergents and cosmetics, paints, food additives, lubricants and fuel additives, rubber in tyres, etc. In spite of the various forms of these materials, many of their properties have common physicochemical origins, such as a large number of internal degrees of freedom, weak interactions between structural elements, and a delicate balance between entropic and enthalpic contributions to the free energy. These properties lead to large thermal fluctuations, a wide variety of forms, sensitivity of equilibrium structures to external conditions, macroscopic softness, and metastable states.

The realization that soft matter contains innumerable examples of symmetry breaking, generalized elasticity, and many fluctuating degrees of freedom has re-invigorated classical fields of physics such as fluids (now generalized to non-Newtonian and structured media) and elasticity (membranes, filaments, and anisotropic networks are all important and have common aspects).