(289a) Biomimetic Hierarchical Assembly in Semi-Crystalline Polymer Nanocomposites

There has been considerable interest in strengthening semi-crystalline polymers while preserving its toughness by incorporating inorganic nanoparticles (NPs). However, to date there is no reported work considering the role of particle dispersion on the material properties – this factor has been shown to be critical in the corresponding case of nanocomposites with amorphous polymer matrix. Here we investigate a nanocomposite material made of semi-crystalline poly(ethylene oxide) and poly(methyl methacrylate) grafted silica NPs. In particular, we focused on understanding the interplay between matrix crystallization and NP self-assembly. We first show that the NPs do not act as nucleating agents since the onset of crystallization temperature is unaffected by the addition of NPs. Although the crystal sizes and the rate of crystallization are reduced in the presence of NPs, the mechanism and thermodynamics of crystallization seems to be unaffected. Furthermore, no remarkable change was observed in the spatial dispersion of NPs upon fast crystallization. However, for slow crystallization, both TEM and X-ray scattering reveal that the system starts to be organized in a “layer-by-layer” architecture, where the NPs are aligned in the amorphous phases intercalated by the crystalline lamellar phases. More importantly, the resulting “sheet-like” NP morphology gives rise to a ~50% increase in the storage modulus as compared to the case where the NPs are individually dispersed. These results open pathways for creating in-situ biomimetic hierarchical structures with improved mechanical properties through a simple, single-step crystallization processing, which could inspire significant practical applications.