Non-linear Viscoelastic Properties

Only a few non-linear viscoelastic properties have been studied with polymers of well-characterized structure. The most prominent of these is the shear-rate dependence of viscosity. Considerable data have now been accumulated for several polymers, extending over a wide range of molecular weights and concen- 

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C. Friedrich, K. Mattes, and D. Schulze, Non-linear Viscoelastic Properties of Polymer Melts as Analyzed by LAOS-FT Experiments, lUPAC Macro 2004, Paris, France, July 4—9, 2004, Paper 6.1.3. 

Contents Chain Configuration in Amorphous Polymer Systems. Material Properties of Viscoelastic Liquids. Molecular Models in Polymer Rheology. Experimental Results on Linear Viscoelastic Behavior. Molecular Entan-lement Theories of Linear iscoelastic Behavior. Entanglement in Cross-linked Systems. Non-linear Viscoelastic-Properties. 

The Fourier transform technique is perfectly general. It may be used also to study non-linear viscoelastic properties (29.30). ... 

Dus, S. J., and Kokini, J. L. (1990). Prediction of the non-linear viscoelastic properties of a hard wheat flour dough using the Bird-Carreau constitutive model. J. Rheol. 34(7), 1069-1084. 

Non-linear viscoelastic behaviour of NR filled with surface-modified nanosilica was prepared with a range of silica compositions. Non-linear viscoelastic properties were measured with change in temperature. A Payne effect was observed at higher silica loadings and evaluated with filler particle size, specific surface area and surface characteristics that were found to be the source of the Payne effect. Storage modulus decreased non-linearly with increasing strain even for unfilled NR. The mechanism included disruption of networks such as... 

Non-linear viscoelastic properties were observed for fumed silica-poly(vinyl acetate) (PVAc) composites, with varying PVAc molar mass and including a PVAc copolymer with vinyl alcohol. Dynamic mechanical moduli were measured at low strains and found to decrease with strain depending on surface treatment of the silica. The loss modulus decreased significantly with filler surface treatment and more so with lower molar mass polymer. Copolymers with vinyl alcohol presumably increased interactions with silica and decreased non-linearity. Percolation network formation or agglomeration by silica were less important than silica-polymer interactions. Silica-polymer interactions were proposed to form trapped entanglements. The reinforcement and nonlinear viscoelastic characteristics of PVAc and its vinyl alcohol copolymer were similar to observations of the Payne effect in filled elastomers, characteristic of conformations and constraints of macromolecules. ... 

High polymer melts and solutions exhibit non-linear viscoelastic properties such as the non-Newtonian dependence of the shear stress on shear rate [125], commonly known as shear-thinning. A number of constitutive equations have been developed to describe the relationship between the shear stress, and the shear rate, y = dvjdy, in simple Couette flow, one of the better known being that of the power law fluid [126]... 

Viscoelasticity is a phenomenon observed in most of the polymers since they possess elastic and viscous characteristics when deformed. The properties such as creep, stress relaxation, mechanical damping, vibration absorption and hysteresis are included in viscoelasticity. If a material shows linear variation of strain upon the application of stress on it, its behavior is said to be linear viscoelastic. Elastomers and soft biological tissues undergo large deformations and exhibit time dependent stress strain behavior and are nonlinear viscoelastic materials. The non-linear viscoelastic properties of solid polymers are often based on creep and stress-... 

Abstract This chapter deals with the non-linear viscoelastic behaviour of rubber-rubber blend composites and nanocomposites with fillers of different particle size. The dynamic viscoelastic behaviour of the composites has been discussed with reference to the filler geometry, distribution, size and loading. The filler characteristics such as particle size, geometry, specific surface area and the surface structural features are found to be the key parameters influencing the Payne effect. Non-Unear decrease of storage modulus with increasing strain has been observed for the unfilled vulcanizates. The addition of spherical or near-spherical filler particles always increase the level of both the linear and the non-linear viscoelastic properties. However, the addition of high-aspect-ratio, fiber-like fillers increase the elasticity as well as the viscosity. 

On the other hand, the Maxwell fluid model explains the response of complex fluids to an oscillatory shear rate. The frequency-dependent behavior of this model, displayed into linear responses to applied shear rates has been found to be applicable to a variety of complex fluid systems. Although the linear viscoelasticity is useful for understanding the relationship between the microstructure and the rheological properties of complex fluids, it is important to bear in mind that the linear viscoelasticity theory is only valid when the total deformation is quite small. Therefore, its ability to distinguish complex fluids with similar micro- and nanostructure or molecular structures (e.g. linear or branched polymer topology) is limited. However, complex fluids with similar linear viscoelastic properties may show different non-linear viscoelastic properties [31]. 

J.L. Leblanc, K.-M. Jager. Investigating non-linear viscoelastic properties of molten carbon black/poly(efhylene-co-butylacrylate) comjxjsites, using Fourier transform rheometry and o1her test techniques. /. Appl. Polym. Sci., 101,4071-4082,2006. 

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