Which is more informative between creep and relaxation experiments?

We present mathematical analysis which compares linear viscoelastic measurements such as creep and relaxation. The analysis is focused on which one is more informative. Since the intervals of relaxation time (or retardation time) of most polymeric materials are much wider than the interval of observation time of conventional rheological measurement, it is not possible to extract perfectly the whole information of material from any rheological measurement. The mathematical analysis is to manifest which experimental method can obtain more information within the same interval of observation. Although the analysis of Jäckle and Richert (2008) means that the width of retardation is wider than that of relaxation, the results of the analysis hold for only viscoelastic solid because their analysis is based on dielectric relaxation. Our analysis shows that creep experiment is more informative than relaxation experiment as for viscoelastic fluid.