MOLECULAR SIMULATIONS OF ELASTOMERIC NETWORKS

摘要

In this work a specialized molecular simulation code has been used to provide details of the micromechanisms responsible for the observed macroscopic behavior of elastomeric materials. In the simulations the polymer microstructure was modeled as a collection of unified atoms interacting by two-body potentials of bonded and non-bonded type. The evolution of representative volume elements with applied uniaxial deformation was studied with a specialized molecular dynamics (MD) simulation technique. A number of interesting observations are directly obtained from the simulations, for example, a very strong correlation between the average bond angle and the stresses in the system is demonstrated. It is also shown that applying a true strain of +-0.7 only causes a change of the average bond angle of about -+5° and a change of the average chain angle of about -+20°. Computed individual chain angles and lengths are compared to the Gaussian statistical model which assumes affine deformation of all chains; results compare favorably at the moderate stretch levels examined. The evolution in average chain angle and length with deformation are found to compare favorably with the 8-chain model (which does not assume affine deformation of all chains). The evolution of stress with strain is decomposed into bonded and non-bonded contributions. The lateral stress is found to increase with strain due to the bonded contribution since the chains rotate toward the principal stretch axis; however, this increase is balanced by a corresponding decrease in the non-bonded contribution. The applied axial stress is thus observed to arise from non-bonded contributions for this case of uniaxial compression. In conclusion, molecular simulations of the type presented in this work appear to be an interesting complement to traditional experiments when developing constitutive equations.