The strain dependence of α relaxation time was systematically investigated for stretched crosslinked polybutadiene (PB) filled with silica nanoparticles via quasi-elastic gamma-ray scattering using time-domain interferometry. The strain dependence of the relaxation time of the α process \({\tau }_{\alpha }\) changed with stress dependence. In particular, \({\tau }_{\alpha }\) increased rapidly up to a strain of 0.2, reaching three times the original value, after which it decreased suddenly and then increased slowly again. This result aligned with the previously reported strain dependence of the α relaxation time of unfilled crosslinked PB. However, the degree of change in the α relaxation time was considerably higher, nearly one order of magnitude larger than that observed for the previous unfilled case. Therefore, silica addition significantly slowed the motion of the α process, leading to significant strengthening of the elongation effect. This significant deacceleration was directly attributed to the microscopic origin of the high elastic modulus of the silica nanoparticle system. This study advances the understanding of the effects of nanoparticle fillers on mechanical properties and molecular mobility, which is crucial for designing high-performance materials for various applications.
