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Complex Fluids

Classic examples of complex fluids are

  • Polymer solutions, mixtures, and melts
  • Mixtures of block copolymers and homopolymers
  • Lyotropic liquid crystals
  • Amphiphilic systems, i.e. mixtures of oil, water and amphiphiles
  • Colloidal suspensions

These complex materials consist of soft matter and are characterized by structural units with typical length scales ranging from nanometres to micrometres. The experimental and theoretical investigations, as well as the understanding of the properties of these materials, pose enormous challenges due to their complexity and the large number of degrees of freedom (motion of functional groups of the molecules, vibrations, cooperative effects, etc.). Furthermore, a large range of length, time and energy scales is relevant for complex fluids.

Soft Condensed Matter

"Soft condensed matter" is a young research area in which a number of disciplines work hand in hand. Studies concentrate on materials such as polymers (plastic molecules) of different shapes and sizes, clusters of large molecules or biological cells. These substances and their mixtures have a lot in common. They can be easily deformed by external forces such as pressure or by shear that come into play during flow - they are "soft". Furthermore, soft matter displays structure in the nanometre to micrometre range, which means that the building blocks are between one billionth and several millionths of a metre in size. They can therefore be studied under an optical microscope as well as with light or neutron scattering. And soft matter is "everywhere": fuel additives and rubber mixtures for tyres consist of soft matter as well as detergents, paints or disposable nappies.

Soft matter can be described by a "magic triangle" whose corner points are colloids, polymers and amphiphiles - the main constituents of soft matter. In between the vertices we find structures such as the chain-like polymers. Furthermore, there are a large number of hybrid systems starting from simple polymer-colloid mixtures like ink up to highly complex biological membranes.