with applied strain. For inter separated nanofiller particles, the polymer chains are
placed between smaller silica particles and these are more difficult to disengage
under load strain. What is more, when larger silica particles are present some
polymer chains may be trapped inside the siloxane networks and behave as filler
in polymer matrix [18].
The authors concluded that the drop in storage modulus with applied strain is
found to be higher for ACM/silica nanocomposites and lower for PVA/silica
systems. For all measured nanocomposites, this effect is higher with increasing
temperature. The reported observations are consistent with relatively weaker
polymer-filler bonding in ACM/silica and stronger interactions (matrix vs filler)
for ENR/silica and PVA/silica nanocomposites [18].
Ramier et al. [53] presented silica-filled vulcanizates based on SBR. The authors
studied the interface between the matrix and the silica, which has been tailored by
grafting either a covering or a coupling using triethoxy silane. The covering agent
(AR) was a monofunctional molecule able to react with the surface silanol groups
while the coupling agent (AC) was bis-(triethoxysilylpropyl)-disulfane (TESPD).
Based on scanning electron microscopy, nanoparticles had an average size from
9 nm (primary particles) to 70 nm (spherical aggregates).
They have proved that unfilled elastomer (SBR) displays linear viscoelastic
behavior, with no change in dynamic storage or loss modulus with strain amplitude.
For the AR samples the authors observed a decrease of the magnitude of the
nonlinear effect with increased presence of covering agent. The untreated silica
shows the highest decrease of modulus vs. strain (the higher Payne effect). For the
AC samples a decrease of the initial modulus G 0
0 at low surface treatment ratio was
observed. The Payne effect amplitude is higher in the case of covering agent
samples. Surface treatment of silica with coupling agents—that promote covalent
bonds between matrix and fillers—reduces the magnitude of the nonlinear behavior.
At the same filler loading, the use of coupling agent causes a reduction in Payne
effect in comparison to covering agent based materials. It should be noted that it is
not possible to distinguish both model (filler-filler and filler-polymer) interactions
when they are modified in the same way by grafting the covering agent [53]. The
authors also have fitted experimental data to the model of debonding of the
polymeric chains from the filler surface proposed by Maier and Goritz [51], and
have gotten good correlation.
Interesting investigations concerning the impact of filler surface modification of
SBR/silica rubber nanocomposites were performed by Sto ¨ckelhuber et al. [54]. The
authors have prepared nanocomposites based on solution-polymerized SBR and
nanofillers: fumed silicas with surface modification by (dimethyldichlorosilane or
bifunctional silane bis(3-triethoxysilylpropyl)-tetrasulfide, precipitated silica
(pretreated with the coupling agent) and carbon black. In their dynamic mechanical
measurements the influence of filler-filler and the filler-rubber interactions was
studied in cured SBR samples. Generally for the filled nanocomposites, the amplitude of the Payne effect decreases. This behavior is visible for the SBR/SiO 2
(unmodified surface) sample (Fig. 16). According to the experimental results
Nonlinear Viscoelasticity in Three Dimensional Filler Reinforced Rubber. . .
75
placed between smaller silica particles and these are more difficult to disengage
under load strain. What is more, when larger silica particles are present some
polymer chains may be trapped inside the siloxane networks and behave as filler
in polymer matrix [18].
The authors concluded that the drop in storage modulus with applied strain is
found to be higher for ACM/silica nanocomposites and lower for PVA/silica
systems. For all measured nanocomposites, this effect is higher with increasing
temperature. The reported observations are consistent with relatively weaker
polymer-filler bonding in ACM/silica and stronger interactions (matrix vs filler)
for ENR/silica and PVA/silica nanocomposites [18].
Ramier et al. [53] presented silica-filled vulcanizates based on SBR. The authors
studied the interface between the matrix and the silica, which has been tailored by
grafting either a covering or a coupling using triethoxy silane. The covering agent
(AR) was a monofunctional molecule able to react with the surface silanol groups
while the coupling agent (AC) was bis-(triethoxysilylpropyl)-disulfane (TESPD).
Based on scanning electron microscopy, nanoparticles had an average size from
9 nm (primary particles) to 70 nm (spherical aggregates).
They have proved that unfilled elastomer (SBR) displays linear viscoelastic
behavior, with no change in dynamic storage or loss modulus with strain amplitude.
For the AR samples the authors observed a decrease of the magnitude of the
nonlinear effect with increased presence of covering agent. The untreated silica
shows the highest decrease of modulus vs. strain (the higher Payne effect). For the
AC samples a decrease of the initial modulus G 0
0 at low surface treatment ratio was
observed. The Payne effect amplitude is higher in the case of covering agent
samples. Surface treatment of silica with coupling agents—that promote covalent
bonds between matrix and fillers—reduces the magnitude of the nonlinear behavior.
At the same filler loading, the use of coupling agent causes a reduction in Payne
effect in comparison to covering agent based materials. It should be noted that it is
not possible to distinguish both model (filler-filler and filler-polymer) interactions
when they are modified in the same way by grafting the covering agent [53]. The
authors also have fitted experimental data to the model of debonding of the
polymeric chains from the filler surface proposed by Maier and Goritz [51], and
have gotten good correlation.
Interesting investigations concerning the impact of filler surface modification of
SBR/silica rubber nanocomposites were performed by Sto ¨ckelhuber et al. [54]. The
authors have prepared nanocomposites based on solution-polymerized SBR and
nanofillers: fumed silicas with surface modification by (dimethyldichlorosilane or
bifunctional silane bis(3-triethoxysilylpropyl)-tetrasulfide, precipitated silica
(pretreated with the coupling agent) and carbon black. In their dynamic mechanical
measurements the influence of filler-filler and the filler-rubber interactions was
studied in cured SBR samples. Generally for the filled nanocomposites, the amplitude of the Payne effect decreases. This behavior is visible for the SBR/SiO 2
(unmodified surface) sample (Fig. 16). According to the experimental results
Nonlinear Viscoelasticity in Three Dimensional Filler Reinforced Rubber. . .
75