Modeling of Self-Healing Polymer Composites Reinforced with Nanoporous Glass Fibers

In recent years there has been increasing interest in designing “smart materials,” specifically, self-healing composites1–9 that can restore their mechanical properties with time or at least reduce deterioration caused by development of microcracks. One of the popular approaches1 7–9 has been to use microcapsules broken by developing microcracks and releasing “glue” material into the damaged matrix. For instance, in recent experiments,1 an epoxy (polymer) was studied, with embedded microcapsules containing a healing agent. Application of a periodic load on a specimen with a crack induced rapture of microcapsules. The healing glue was released from the damaged microcapsules, permeated the crack, and a catalyst triggered a chemical reaction which re-polymerized the crack. We note, however, that a significant amount of microcapsules embedded in the material may actually weaken its mechanical properties and reduce its usable lifetime (though it was noted1 that small amount of microcapsules actually increased the material toughness). Thus, the density of the “healing” microcapsules is one of the important system parameters to optimize in any modeling approach. Defects of nanoscale sizes are randomly distributed over the material. Mechanical loads during the use of the material cause formation of craze fibrils along which microcracks develop. This ultimately leads to degradation of the material. Triggering self-healing mechanism at the nanoscale offers several advantages for a more effective prevention of further propagation and growth of microcracks, specifically, it is hoped that nanoporous fibers with glue will heal smaller damage features, thus delaying the material fatigue. This is in contrast with the earlier studied several-micron size capsules,1 9 that basically