The relative placement of linear viscoelastic functions in amorphous glassy polymers

A procedure is described and analyzed for the determination of the relative placement of linear viscoelastic functions and their relative relaxation/retardation spectra for a commercial polycarbonate (LEXAN GE). The complete set of viscoelastic functions in creep and relaxation was obtained from two simple experimental data, namely the linear viscoelastic response in shear and the pressure volume temperature (PVT) behavior. The dimensionless bulk compliance was extracted from PVT data showing that it coincides with the memory function appearing in the Kovacs, Aklonis, Hutchinson, Ramos phenomenological theory [Kovacs, A. J., J. J. Aklonis, J. M. Hutchinson, and A. R. Ramos, J. Polym. Sci., Polym. Phys. Ed. 17, 1097 (1979)]. Our results are compared with the relevant literature data obtained on different polymers and show that polycarbonate fulfills simultaneously the responses features concerning the relative placement of the bulk and shear moduli [Kono, R. J., Phys. Soc. Jpn. 15, 4 (1960)], the shapes of the bulk and the shear retardation spectra [Bero, C. A., and D. J. Plazek, J. Polym. Sci., Part B: Polym. Phys. 29, 39-47 (1991)], the relative placement of the bulk and shear compliance [Deng, T. H., and W. G. Knauss, Mech. Time-Depend. Mater. 1, 33-49 (1997); Sane, S. B., and W. G. Knauss, Mech. Time-Depend. Mater. 5, 293-324 (2001)], the relative placement of bulk modulus and shear compliance [Meng, Y., and S. L. Simon, J. Polym. Sci., Part B: Polym. Phys. 45, 3375-3385 (2007)], the relative placement of the bulk compliance and the axial relaxation modulus [Knauss, W. G., and I. Emri, Polym. Eng. Sci. 27, 86-100 (1987)], and the shape of the Poisson's ratio [Lakes, R. S., Cell. Polym. 11, 466-469 (1992); Von Koppelmann, J., Rheol. Acta 1, 20-28 (1958); Ferry, J. D., Viscoelastic Properties of Polymers, 3rd ed. (Wiley, New York, 1980)], and its scaling with the shear modulus [O'Brien, D. J., N. R. Sottos, and S. R. White, Exp. Mech. 47, 237 (2007)].