Rheological characterization of polymer gels and networks

Although rheological measurements are still not familiar to all workers on gels and networks, a recent definition of the gel state is based upon rheological criteria. Small deformation time, strain and frequency sweeps enable the investigation of gelling properties on a curing system. These experiments have been improved by recent technical advances such as 'multi-wave' experiments, in which the simple sine wave history is replaced by superimposed harmonics, or more complex oscillatory deformations. Large deformation rheometry involves testing a gel sample either in tension/compression or in shear, up to and sometimes past the yield or failure point. Strain, temperature and concentration effects can be investigated using Smith's failure envelope.