Resolving structure-property-dynamics relationships in model polymer nanocomposite systems*

Understanding the origins of mechanical enhancement in polymer-nanoparticle composites (PNC) is necessary to design materials with optimized mechanical properties. We use a combination of techniques to resolve the dynamics-structure-property relationships governing mechanical enhancement in a model PNC system of attractive SiO2 nanoparticles embedded in a glassy P2VP polymer matrix over a wide range of NP concentrations (1 – 25 vol.%). By tuning the interparticle distance between neighboring NPs, the formation of the proposed “structural bridge” and the resulting contribution to mechanical enhancement are resolved [1]. The nanoscale structure is investigated by SAXS and TEM while the micro/macro dynamics are resolved by x-ray photon correlation spectroscopy (XPCS) and shear rheology respectively. As concentration increases, the characteristic relaxation times increase dramatically. The dynamics transition to collective motion at the gel point, which correlates to the formation of a sample spanning network. Identification of “rubbery” and “glassy” bridges are discussed in the context of the observed dynamics. [1] Chen, Q.; et al. ACS Macro Lett. 2015, 4 (4), 398–402.