| Author | R. C. Picu, G. Loriot, J. H. Weiner |
|---|---|
| Title | Toward a unified view of stress in small-molecular and in macromolecular liquids |
| Year | 1999 |
| Journal | Journal of Chemical Physics |
| Volume | 110(9) |
| Pages | 4678-4686 |
| Abstract | We consider a family of molecular liquids, each consisting of linear molecules with N covalent bonds, focusing specifically on N=1 (diatomic liquid), N=3 (four-atom molecular liquid), and N=200 (macromolecular liquid). The bonded and nonbonded potentials, ub and unb , are the same for each system, with ub representing stiff linear springs and unb corresponding to the repulsive portion of the Lennard-Jones potential. The relaxation of the stress difference , following a constant-volume elongation of the system, is determined in terms of interatomic interactions by nonequilibrium molecular dynamics simulations. It is found that the nonbonded interactions make the principal contribution to while the bonds make a negative contribution. For all systems studied it is found that, following a short induction period after the start of relaxation, , where is a measure of the individual bond orientation and the proportionality constant within simulation accuracy, for . The principal difference between the behavior for small and large is the rate at which decays. An explanation of the broad applicability of the relation is presented in terms of the concepts of steric shielding, intrinsic interaction distributions, and intrinsic stresses. The failure of this relation during the short induction period is explained in terms of anisotropies in atom distributions present immediately after deformation. |