Interfacial relaxation mechanisms in polymer nanocomposites through the rheological study on polymer/grafted nanoparticles

- Rheological properties of PLLA nanocomposites were studied.
- A sequential relaxation framework was built by relaxation spectrum for polymer nanocomposites.
- The relaxation times of the interfacial chains in polymer nanocomposites were obtained.
- The relaxation mechanism on the interface was affected by the topology of grafted chains.

Polymer grafted nanoparticles with different surface properties have been prepared and widely used in different fields recently. In this study, through the rheological study on the strength of interfacial adhesion relevant to the complex viscoelasticity and relaxation response of the well-defined polymer (polylactide, PLLA) grafted-nanoparticles (silica) mixed with free chains of the same polymer nanocomposites in melt state, we investigated the different interfacial entanglement and relaxation mechanisms of the polymer grafted nanocomposites (PGN), to bridge the relationship between the micro and macro-properties of PGN. The AFM observation illuminated that circles one by one were formed in “grafting from” prepared SiO2 (GF), while core-shell morphology found in “grafting to” prepared SiO2 (GT), because of the different surface properties of the modified SiO2. The interface relaxation was characterized around 300 s in the GT5 nanocomposites, due to the entanglement between the long grafted and matrix chains, which also contributed lots to the rheology properties enhancement, such as the improving viscosity. Combining the relaxation spectrum and stress relaxation testing, the relaxation units in different time scales, from short time to long time, were illuminated. Also the relaxation of the interfacial chains in different situations, through the introduction of the absorption and reptation models, was proposed to explain our observations. The comparative study reminded us that the strong interfacial interactions or the long interfacial relaxation time aroused by the entanglement, were essential for successfully preparing polymer nanocomposites.