Depolarized Light Scattering from Swollen-Filled Rubber
When rubber containing glass sphere filler particles swells, the swelling is inhomogeneous in that tangential strain is not permitted at the surface of the filler particle providing the rubber remains attached to this particle. Consequently, the degree of swelling in the immediate vicinity of the filler particle will be less than in the bulk of the rubber and there will be a gradient of swelling with distance away from the particle. This leads to a stress gradient in which the radial and tangential component of stress are different. The theory of this effect has been developed by Sternstein. The rubber will become birefringent as a result of this stress gradient leading to a difference between radial and tangential refractive indices. Wilkes and Stein have developed a from material containing such a spherically symmetrical refractive index difference gradient. The equations for this gradient from Sternstein’s theory were inserted in the Wilkes-Stein theory and the HV light scattering patterns obtained by observing the sample between cross polaroids has been calculated. Experimental patterns have been obtained using synthetic cis-1,4-polyisoprene rubber filled with small glass spheres. The patterns are in agreement with the theoretically calculated ones and verify the theory of Sternstein. With a dispersion of glass beads of different sizes, the higher order scattering maxima must smooth out, but if the scattering is obtained from single large glass beads these maxima may be resolved.
KeywordsFiller Particle Glass Sphere Scattering Pattern Tangential Strain Silica Filler
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