Glossary: Mechanical and rheological properties of polymers

1. complex fluid: opposed to simple fluid; non-newtonian fluid characterized by intricate visco-elastic rheological behavior.

2. relaxation time &tau: time equilibrium fluctuations need to relax. The relaxation time of a polymer chain is (normally) given by the time the chain needs to diffuse over its own size R. For strongly entangled polymer melts this implies an increase of the relaxation time (at least) as the cube of the chain length N.

3. rheology: here: phenomenological study of conditions and consequences of flow and creep of polymer materials.

4. soft matter: Roughly speaking, soft matter consists of materials whose constituents have a mesoscopic size (10³-10⁵nm) for which k_BT is the important energy scale (whence the softness at ambient conditions). Examples are polymers, colloidal suspensions, liquid crystals, or fluid membranes.

5. viscosity: coefficient relating the shear stress to the shear strain rate. It measures the rate of momentum transfer across a transverse velocity gradient.