[SY-H6] Coarse-Grained Molecular Dynamics Simulation of Filled Rubber under Cyclic Tensile Deformation
Filler morphology, radius, and strength of the filler-polymer interaction impact the physical properties of filled rubber. It is crucial to understand relationships between them so as to improve tire performances. Four large-scale coarse-grained molecular dynamics models were created. The first model is a reference model in which filler particles are distributed in a lattice pattern. The second model is an aggregated model including a non-homogenous filler distribution. The third model is a small particle size model in which small particles are distributed with identical morphology and volume fraction with the reference model. The forth model is a weak interaction model. The polymer-filler interaction is weaker than the reference model, even though the morphology and the particle size match the reference model.
Comparing stress-strain curves, we confirmed that effects of them which are observed in experimental results; filler aggregates, small particles, and strong interaction make modulus and hysteresis greater, were reproduced qualitatively. Measuring a polymer density distribution and a change of polymer chains bridging fillers, it was found that an increase of polymer density around fillers induced by the polymer-filler attractive interaction grows the modulus of the polymer phase and irreversible changes of polymer chains cause hysteresis. We determined that these changes observed in all models are fundamental mechanisms of filled rubber. Comparing the stress-strain curves of the reference model and the aggregated model, we found that the differences are attributed to filler stress. Fillers are to be contacted with another filler particle during deformation and filler stress grows when fillers are aggregated. Comparing the reference model and the weak interaction model, we found that the number and force per a bond of extended chains in the reference model, which are main sources of polymer stress, are greater than the weak interaction model, even though length of the extended chains are much the same. These differences of polymer stress make modulus and hysteresis greater.
Last, a significant increase of the number of extended chains grows polymer stress, when fillers are small and the volume fraction of filler is identical with the reference model. Thus the modulus and hysteresis become greater.
Comparing stress-strain curves, we confirmed that effects of them which are observed in experimental results; filler aggregates, small particles, and strong interaction make modulus and hysteresis greater, were reproduced qualitatively. Measuring a polymer density distribution and a change of polymer chains bridging fillers, it was found that an increase of polymer density around fillers induced by the polymer-filler attractive interaction grows the modulus of the polymer phase and irreversible changes of polymer chains cause hysteresis. We determined that these changes observed in all models are fundamental mechanisms of filled rubber. Comparing the stress-strain curves of the reference model and the aggregated model, we found that the differences are attributed to filler stress. Fillers are to be contacted with another filler particle during deformation and filler stress grows when fillers are aggregated. Comparing the reference model and the weak interaction model, we found that the number and force per a bond of extended chains in the reference model, which are main sources of polymer stress, are greater than the weak interaction model, even though length of the extended chains are much the same. These differences of polymer stress make modulus and hysteresis greater.
Last, a significant increase of the number of extended chains grows polymer stress, when fillers are small and the volume fraction of filler is identical with the reference model. Thus the modulus and hysteresis become greater.