Modulus recovery kinetics and other insights into the payne effect for filled elastomers

Abstract

The nonlinear viscoelastic behavior of filled elastomers is examined in detail using a variety of samples including carbon-black filled natural rubbers and fumed silica filled silicone elastomers. New insights into the Payne effect are provided by examining the generic results of sinusoidal dynamic and constant strain rate tests conducted in true simple shear both with and without static strain offsets. The effect of deformation history is explored by probing the low amplitude modulus recovery kinetics resulting from a perturbation by a large strain deformation such as a sinusoidal pulse or the application or removal of a static strain. It is found that a static strain has no effect on either the fully equilibrated dynamic (storage and loss) moduli or the incremental stress-strain curves taken at constant strain rate. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the type of perturbation. Modulus recovery is complete but requires thousands of seconds, and is independent of the static strain. The results suggest that deformation sequence is as critical as strain amplitude in determining the properties, and that currently available theories are inadequate to describe these phenomena. The distinction between fully equilibrated dynamic response and transitory response is critical and must be considered in the formulation of any constitutive equation to be used for design purposes with filled elastomers.

Enthalpic relaxation of silica–polyvinyl acetate nanocomposites

“…Additionally, a static strain has no effect on the observed Payne effect. 3 Why would a glassy layer disappear when subjected to a static stress but not a dynamic stress? In summary, the glassy layer as a root cause of the reinforcement mechanism raises more questions than it answers.…”

“…It has also been shown that the Payne effect is related to the dynamic, and not static, component of the strain history and that the Payne effect would vanish at very low strain rates. 3 If a glassy layer is responsible for the high reinforcement then why does reinforcement vanish if observed at a slow strain rate? Additionally, a static strain has no effect on the observed Payne effect.…”

“…These models can be categorized based on the root origin of the phenomena, that is, some of them are based on the spatial distribution of the fillers, such as agglomeration, deagglomeration, filler percolation threshold, or the alteration of chain dynamics near the filler surface, with both short-or long-range effects and with finite bond lifetime or permanently adhered bonds that form glassy layers near the filler particles. [1][2][3][4] The presence of a glassy layer at the filler surface as the underlying mechanism of reinforcement has been proposed by several authors. [5][6][7][8] The model states that a glassy layer or layers with a gradient of glass transition temperature persists near the walls of the filler even if the temperature is above the glass transition Correspondence to: S. Amanuel (E-mail: amanuels@union.…”

“…In this regard, there are several observations that have been made in filled elastomers well above the glass transition temperature that suggest alternate explanations to the formation of a glassy layer. 3,4 These explanations are based on the labile bonding of the polymer to the filler surfaces and the resultant effects this bonding has on the reduction of conformational entropy of the matrix chains. 4 Thus, entropic hardening is the result of enthalpic bonding of the polymer segments to the filler surfaces, but this bonding need not produce a glassy layer to be effective at producing high reinforcement through far-field interactions transmitted by chain entanglements.…”

Flocculation, Reinforcement, and Glass Transition Effects in Silica-Filled Styrene-Butadiene Rubber

“…Viscoelastic behavior is extremely sensitive to the structure of the filler network in particlereinforced polymers, and the strain-dependence of dynamic mechanical response after complex deformation histories can reveal details of the heterogeneity and kinetics of network break-up and recovery. [48][49][50][56][57][58][59][60] When the particles are electrically conductive (e.g., carbon black), electrical resistance testing is another useful method to study the structure of the percolated filler network. [61][62][63][64] With the exception of transmission electron microtomography, 65,66 it is difficult to observe differences in the three-dimensional nature of jammed particle networks using microscopy.…”