| Abstract: | As glassy polymers are usually somewhat brittle, several blending techniques are used to toughen these materials and to increase their impact strength. The microstructures of toughened polymers are complicated, as are their mechanical damage mechanisms. Moreover, these materials are mostly opalescent or even opaque, which renders difficult any optical investigation of the damage process. The scale of the damage generally ranges from nanometers to several micrometers, thus requiring a large panel of experimental techniques to investigate its microstructural evolution. When illuminated with a light beam, any non-perfectly transparent body will scatter light with a scattering pattern depending on the size, shape, and location of the microscopic light scatterers it contains. If the body is highly opaque, an incident light beam, if not absorbed, is scattered successively by several scatterers before emerging again at the front surface of the body. It has recently been shown that there is a coherent interference enhancement of the randomly multiple scattered light in a small angle range around the exact reverse direction of the incident light. This so-called coherent backscattering cone can be analyzed in terms of the size, shape and density of the scatterers. In this work, this technique is applied to a rubber-toughened PMMA containing core-shell (hard core) particles, an initially transparent material that becomes progressively opaque during mechanical damage under stress. The damage mechanism within the rubber particles is compared with the size and shape of the light scatterers inferred from coherent backscattering and light transmission measurements. |
