Intermediate Polymer Relaxation Explains the Anomalous Rheology of Nanocomposites with Ultrasmall Attractive POSS Nanoparticles

Abstract

The rheological properties of entangled polymers loaded with very small, strongly attractive polyhedral oligomeric silsesquioxane (POSS) fillers differ from that of nanocomposites with larger fillers by (1) the shorter breadth of the entanglement plateau and (2) the relatively unchanged terminal viscosity with increasing POSS loading. Although such anomalous rheological properties can rewrite the property–processing map of materials (e.g., high glass transition temperature and low viscosity), their mechanism remains unclear. In this study, we report that polymer relaxations on intermediate time scales between α and entire-chain relaxation, so-called “slower processes”, are responsible for this unusual rheological behavior of poly­(2-vinylpyridine)/octa­(aminophenyl)­silsesquioxane (P2VP/OAPS) nanocomposites. To uncover the effects of entanglements on the nanocomposite dynamics, rheometry is used for variable matrix molecular weights. Results show a systematic change in the rheological response, which is independent of the molecular weight, and in turn, the presence of entanglements. This supports a physical interpretation that a slower process dominates the rheological response of the material at intermediate frequencies on length scales larger than the segment length or the OAPS diameter, while the underlying physical time scales associated with the entanglement relaxation remain unchanged. Such insights are anticipated to assist the future rational design of other highly attractive and ultrasmall nanoparticles that enable a fine-tuned rheological response of nanocomposites across multiple length scales.

Fast Processing Affects the Relaxation of Polymers: The Slow Arrhenius Process Can Probe Stress at the Molecular Level

“…As stress significantly affects the mechanical response of polymers, the correlation between σ res and Δε SAP suggests that the SAP should be detected also in rheological measurements and in experiments of mechanical spectroscopy. Recent works on polymers support this claim. , Finally, although the approach used to spotlight such relation is empirical and might suffer from a series of approximations including the differences in the T g of the polymers and in the chemical nature of the substrateswe hope that our work will stimulate further discussion on how stress affects the relaxation dynamics …”

Vehicular and Core–Shell Nanoparticle Diffusion in Attractive Entangled Polymer Melts

“…Previous work has clearly established that the spatial distribution of NPs significantly impacts processability and properties, including mechanical properties, rheology, and gas permeability within PNCs. − To achieve and maintain the desired properties, understanding and predicting NP diffusion are critically important. Factors such as NP size, NP shape, NP concentration, and the interaction between polymer and NPs must be managed to achieve desired NP distributions and properties for effective PNC applications. − PNCs with strong attractions between the NPs and polymer matrix are distinguished by improved NP dispersion and maintain industrially relevant processability advantages compared with their neutral counterparts.…”