What’s wrong with the moduli Charley Brown? or Get the H out and go to L

Abstract

For unknown psychological reasons, the vast majority of viscoelastic measurements are presented as dynamic or stress relaxation modulus functions. To examine only modulus functions appears to be acceptable, because within a constant or two, all of the complete viscoelastic functions are mathematically equivalent. It is pointed out here, that most data are not practicably equivalent and that in numerous instances the compliance functions are more revealing concerning molecular orientational dynamics; especially those that are not influenced by viscous flow. The presence of shoulders or plateaus exhibited by the dynamic storage modulus G′ or the stress relaxation modulus G(t) functions, which can be mistaken for molecular entanglement plateaus, are shown to be present in some systems that contain no effective entanglements. The obfuscation caused by the viscous deformation in the terminal zone of behavior is emphasized. The additivity of different molecular mechanisms contributing to the compliance functions demand that decomposition be carried out on these functions, before further analysis is possible. Since the results from any dynamic measurement, which yields both storage and loss components of the modulus, can be algebraically transformed into the compliance components, investigators have nothing to lose but possibly much to gain by including the examination of the compliances as well as the moduli.