Paper 8.1

Paper Number 8.1

Investigation of the Microscopic Viscoelastic Property for Cross-linked Polymer Network
by Molecular Dynamics Simulation

Yuuki Masumoto[1]

You Iida

TOYO TIRE & RUBBER CO., LTD. Tire Technical Center

2-2-13 Fujinoki, Itami, Hyogo, 664-0847 Japan

Email: masu@toyo-rubber.co.jp

Voice: +81-72-775-9246

Fax: +81-72-775-9026

The purpose of this work is to develop a new analytical method for simulating the microscopic mechanical property of the cross-linked polymer system using the coarse-grained molecular dynamics simulation. This new analytical method will be utilized for the molecular designing of the tire rubber compound to improve the tire performances such as rolling resistance (RR) and wet traction.

For the first, we evaluate the microscopic dynamic viscoelastic properties of the cross-linked polymer using coarse-grained molecular dynamics simulation. This simulation has been conducted by the COGNAC simulator in the OCTA (http://octa.jp/). To simplify the problem, we employ the bead-spring model, in which a sequence of beads connected by springs denotes a polymer chain. The linear polymer chains that are cross-linked by the cross-linking agents express the three-dimensional cross-linked polymer network. In order to obtain the microscopic dynamic viscoelastic properties, oscillatory deformation is applied to the simulation cell. By applying the time-temperature reduction law to this simulation result, we can evaluate the dynamic viscoelastic properties in the wide deformational frequency range including the rubbery state.

Then, the stress is separated into the nonbonding stress and the bonding stress, we confirm the contribution of the nonbonding stress is larger at lower temperature. On the other hand, the contribution of the bonding stress is larger at higher temperature.

Finally, analyzing a change of microscopic structure in dynamic oscillatory deformation, we find out that the temperature/frequency dependence of bond stress response to a dynamic oscillatory deformation depends on the temperature dependence of the average bond length in the equilibrium structure and the temperature/frequency dependence of a bond orientation. We show our simulation is a useful tool for studying the microscopic properties of a cross-linked polymer.