Cauchy relation in relaxing liquids

The Cauchy-like relation M-infinity=A+BG(infinity) has recently been found to hold for the high frequency limit values of the longitudinal modulus M-infinity and transverse modulus G(infinity) of viscoelastic liquids, with B similar or equal to 3 in all the investigated systems. The Brillouin scattering results here reported for curing epoxy systems and thermal glass formers give evidence for the validity of a Cauchy-like relation M-'=A+BG(') for the real part of the elastic moduli measured at finite frequencies. Our results suggest as well the validity of a pure Cauchy relation Delta M=3 Delta G for the relaxation strengths of longitudinal and shear moduli in relaxing liquids. (c) 2008 American Institute of Physics.