elastomer homocomposites by [2] are remarkable rubbers exhibiting exceptional
fracture toughness. Composed of linear and flexible acrylate chains, they combine
reversible elasticity and strain-dependent damage with nearly no viscoelastic
dissipation.
The multinetwork systems have a complex structure owing to the distinct
prestretch in every generation of network, a specific feature of the synthesis protocol.
Typically in a double-network system, the first network is highly prestretched with
tensile (pre)stress. In systems with two or more embedded networks, the (pre)stress
is different in each network generation. This unique interplay of local network
structure, cross-link density and inbuilt (pre)stress are known to influence the overall
mechanical performance of the elastomers [3]. The toughening mechanism is attributed to the sacrificial bonds from the prestretched networks – confirmed by
mechanoluminescence experiments [3]. The composites also show noticeable
Mullins effect [4, 5], strong localized softening due to scission of covalent bonds
followed by a stable necking process, a phenomenon never observed before in
elastomers.
One of the critical research themes is to uncover the influence of the microscopic
architecture on the mechanics of the material. The parameters that define the design
of the multinetwork structures is huge, and the exact influence of these parameters on
the mechanical response is still poorly understood. Since prestress is tightly linked to
network architecture, the use of molecular dynamics simulations to shed light on
these relations requires careful construction of the network architectures. In Sect.
3.4, we present a method based on lattice random walks to do this. Then, we focus
our efforts on understanding how the presence of covalent cross-links between the
two generations of a double-network structure affects the mechanics. We find that
such intergenerational cross-links have crucial influence on the stress transfer and
fracture of double-network systems. We describe the methods to model the topology
of the networks and explore fracture dynamics at the microscopic bond level in Sect.
4.6.
2.1.2 Polymer-Particle Composites: Nanocomposites and Filled
Rubbers
A further way to enhance the properties of polymer materials such as elastomers is to
blend them with particulate filler material. Even at relatively small filler fractions, the
synergy between a polymer matrix and small inclusions may be curiously strong – a
fact that has been exploited extensively in the tire industry where carbon black, a
material produced by the incomplete combustion of many heavy petroleum derivatives, is incorporated into an elastomer matrix. Such nanocomposites – carbon blackenriched rubbers, with matrices typically composed of synthetic styrene-butadiene
copolymers – present drastically improved properties most notably, among which
are a greatly improved toughness, wear resistance and stiffness. Specific types of
silica fillers (and filler-matrix attachments) can lead also to improved rolling resistance. This rolling resistance is a key determinant factor for the energy efficiency of
Rheology, Rupture, Reinforcement and Reversibility: Computational Approaches. . .
67
fracture toughness. Composed of linear and flexible acrylate chains, they combine
reversible elasticity and strain-dependent damage with nearly no viscoelastic
dissipation.
The multinetwork systems have a complex structure owing to the distinct
prestretch in every generation of network, a specific feature of the synthesis protocol.
Typically in a double-network system, the first network is highly prestretched with
tensile (pre)stress. In systems with two or more embedded networks, the (pre)stress
is different in each network generation. This unique interplay of local network
structure, cross-link density and inbuilt (pre)stress are known to influence the overall
mechanical performance of the elastomers [3]. The toughening mechanism is attributed to the sacrificial bonds from the prestretched networks – confirmed by
mechanoluminescence experiments [3]. The composites also show noticeable
Mullins effect [4, 5], strong localized softening due to scission of covalent bonds
followed by a stable necking process, a phenomenon never observed before in
elastomers.
One of the critical research themes is to uncover the influence of the microscopic
architecture on the mechanics of the material. The parameters that define the design
of the multinetwork structures is huge, and the exact influence of these parameters on
the mechanical response is still poorly understood. Since prestress is tightly linked to
network architecture, the use of molecular dynamics simulations to shed light on
these relations requires careful construction of the network architectures. In Sect.
3.4, we present a method based on lattice random walks to do this. Then, we focus
our efforts on understanding how the presence of covalent cross-links between the
two generations of a double-network structure affects the mechanics. We find that
such intergenerational cross-links have crucial influence on the stress transfer and
fracture of double-network systems. We describe the methods to model the topology
of the networks and explore fracture dynamics at the microscopic bond level in Sect.
4.6.
2.1.2 Polymer-Particle Composites: Nanocomposites and Filled
Rubbers
A further way to enhance the properties of polymer materials such as elastomers is to
blend them with particulate filler material. Even at relatively small filler fractions, the
synergy between a polymer matrix and small inclusions may be curiously strong – a
fact that has been exploited extensively in the tire industry where carbon black, a
material produced by the incomplete combustion of many heavy petroleum derivatives, is incorporated into an elastomer matrix. Such nanocomposites – carbon blackenriched rubbers, with matrices typically composed of synthetic styrene-butadiene
copolymers – present drastically improved properties most notably, among which
are a greatly improved toughness, wear resistance and stiffness. Specific types of
silica fillers (and filler-matrix attachments) can lead also to improved rolling resistance. This rolling resistance is a key determinant factor for the energy efficiency of
Rheology, Rupture, Reinforcement and Reversibility: Computational Approaches. . .
67