Molecular Reorganization
Kinetic properties describe the rate at which long chain molecules return to an equilibrium state after the removal of a deforming force. Polymer relaxation times reflect the internal friction and mobility of the molecular segments as they untangle and slide past each other. These durations vary from fractions of a microsecond to several decades depending on the length of the chains and the degree of cross linking.
Spectrum Distribution
Single values are rarely sufficient to describe a material because the different scales of motion within the chains create a broad distribution of responses. The study of polymer relaxation times involves the use of a prony series or a similar sum of exponential functions to map this distribution. This map is known as the relaxation spectrum and identifies which motions dominate at different temperatures.
It provides a complete profile of the time dependent mechanical properties.
Temperature Sensitivity
Cooling the material increases the viscosity and stretches these durations to much longer values. Polymer relaxation times are linked to the glass transition temperature where the material switches from a hard solid to a flexible rubber. Measurement of these times requires dynamic mechanical analysis across a range of frequencies.
Viscoelastic Influence
Engineering designs must account for these time scales to prevent the buildup of internal stresses. Polymer relaxation times determine how quickly a seal recovers its shape.
