A model for the degradation of polyimides due to oxidation

Polyimides, due to their superior mechanical behavior at high temperatures, are used in a variety of applications that include aerospace, automobile and electronic packaging industries, as matrices for composites, as adhesives etc. In this paper, we extend our previous model in [S. Karra, K. R. Rajagopal, Modeling the non-linear viscoelastic response of high temperature polyimides, Mechanics of Materials, In press, doi:10.1016/j.mechmat.2010.09.006], to include oxidative degradation of these high temperature polyimides. Appropriate forms for the Helmholtz potential and the rate of dissipation are chosen to describe the degradation. The results for a specific boundary value problem, using our model compares well with the experimental creep data for PMR-15 resin that is aged in air.Comment: 13 pages, 2 figures, submitted to Mechanics of Time-dependent Material

A graph theoretical approach to the elucidation of reaction mechanisms: Analysis of the chlorine electrode reaction

A methodology and algorithm are proposed in this work to conceive a limited set of dependent elementary reaction steps for a reaction mechanism by exploiting the reaction route (RR) graph of the mechanism. These steps are constrained by the conservation principles and must be subjected to thermodynamic feasibility studies. This method is expected to aid in the conception of new steps, which might otherwise be ignored, especially in the case of large mechanisms. In order to illustrate the method, it is applied to the chlorine electrode reaction mechanism. The result indicated that a reaction pathway consisting of one of the newly proposed steps is the dominant one. This example illustrated the potential of the proposed method to identify new steps to a mechanism and thereby help in mechanism elucidation. However, these new steps must be subjected to further critical study before they can be accepted