Search

Recently, Friedrich proposed an empirical model for linear viscoelastic fluids corresponding to a constitutive equation with fractional derivatives [Phil. Mag. Lett., 66, 287 (1992)]. For this model, the relaxation modulus, the dynamic moduli, the relaxation time spectrum, and other material functions have been explicitly calculated as a function of the few parameters that characterize a viscoelastic fluid within this model. By fitting this model to experimental data, the model parameters can be determined and other material functions, in particular the relaxation time spectrum, can be calculated immediately. This paper reports to what extent this method, which may be called analytical inversion, is appropriate for the determination of relaxation time spectra. For that purpose, the spectra of a number of very different polymeric materials are determined with this method. The spectra calculated in this way are compared with the spectra obtained by nonlinear regularization. It turns out that the empirical model describes the linear viscoelastic properties of a variety of different materials with high accuracy. Keeping in mind that the determination of the relaxation time spectrum requires the solution of an ill-posed problem, the agreement between the relaxation time spectra obtained by analytical inversion and by regularization is satisfactory for these materials., INTRODUCTION The determination of the relaxation time spectrum from experimental data for a material function is one of the oldest tasks in rheology. It is, however, not an easy task, [...]

Viscoelastic properties of the filled polymeric composites taking into account influence on them of an interphase layer (polymer which has changed the properties as a result of interaction with a surface of filler particles) are defined. Effective viscoelastic properties of the filled polymeric materials were defined by means of an iterative method of the averaging based on the idea of renormal group transformation. Comparison of calculation with experimental data which shows on their good enough the coordination is spent. The analysis of influence of an interphase layer and the size of filler particles on viscoelastic properties of the filled polymeric composites is carried out. Quantitative estimations of properties of an interphase layer which have shown on their essential difference from properties of polymer are received. [ABSTRACT FROM AUTHOR]