The reduction in both the storage and loss moduli for the double network is not
only found in the peroxide-cured double networks, the effects described above are
also observed in sulfur-cured double networks. Wang et al. [34] produced a sulfurcured double networks using synthetic cis-1,4-polyisoprene (IR-1, λR ¼ 1.15 and
IR-2, λR ¼ 1.30). The measurements were carried out differently, via torsion of a
rectangular strip. This deformation involves bending as well as shear modes
perpendicular to the double network principle orientation. The G
0 for the two
double networks and a (control) single network are shown in Fig. 6. In comparison
to the isotropic sample, the double networks exhibit a marked reduction in the
plateau associated with the filler network. Compared with the peroxide-cured
double networks, the sulfur-cured double networks having a larger residual strain
appear to have a weaker Payne effect. The trivial variations may be related to the
preparation and processing of the materials, but no consistent trend with λR was
observed [34].
It is noteworthy that there is orientation along the stretching direction during the
second cure. However, the lower dynamic hysteresis observed by Wang [34] is
independent of the deformation direction: dynamic measurements using three
different geometries—shear (in the plane of the double network principle orientation), uniaxial extension (parallel to the orientation of the double network), and
torsion (combining bending and shear deformations). For all cases, the double
networks showed lower hysteresis. Thus, the import of a double network structure
may be a generally useful approach to more energy efficient elastomers.
Fig. 6 Dynamic storage
modulus of double networks
(hollow symbols) and the
corresponding single
network ( filled symbols),
measured using torsional
shear of rectangular strips at
1 Hz and RT. The absence
of a filler network in the
double networks occasions
the disappearance of the
strain-dependent plateau
[34]
174
Y. Chen and C. Xu
only found in the peroxide-cured double networks, the effects described above are
also observed in sulfur-cured double networks. Wang et al. [34] produced a sulfurcured double networks using synthetic cis-1,4-polyisoprene (IR-1, λR ¼ 1.15 and
IR-2, λR ¼ 1.30). The measurements were carried out differently, via torsion of a
rectangular strip. This deformation involves bending as well as shear modes
perpendicular to the double network principle orientation. The G
0 for the two
double networks and a (control) single network are shown in Fig. 6. In comparison
to the isotropic sample, the double networks exhibit a marked reduction in the
plateau associated with the filler network. Compared with the peroxide-cured
double networks, the sulfur-cured double networks having a larger residual strain
appear to have a weaker Payne effect. The trivial variations may be related to the
preparation and processing of the materials, but no consistent trend with λR was
observed [34].
It is noteworthy that there is orientation along the stretching direction during the
second cure. However, the lower dynamic hysteresis observed by Wang [34] is
independent of the deformation direction: dynamic measurements using three
different geometries—shear (in the plane of the double network principle orientation), uniaxial extension (parallel to the orientation of the double network), and
torsion (combining bending and shear deformations). For all cases, the double
networks showed lower hysteresis. Thus, the import of a double network structure
may be a generally useful approach to more energy efficient elastomers.
Fig. 6 Dynamic storage
modulus of double networks
(hollow symbols) and the
corresponding single
network ( filled symbols),
measured using torsional
shear of rectangular strips at
1 Hz and RT. The absence
of a filler network in the
double networks occasions
the disappearance of the
strain-dependent plateau
[34]
174
Y. Chen and C. Xu