Viscosity reduction in polymer nanocomposites: Insights from dynamic neutron and X‐ray scattering

Abstract

The addition of nanoparticles to a polymer matrix can in certain cases induce a reduction in viscosity, with respect to the pure matrix, in the resulting composites. This counterintuitive phenomenon cannot be explained using the most common rheological models. For this reason, it has been chosen as a good example in this paper to demonstrate the value and methods of dynamic X-ray and neutron scattering techniques for the investigation of polymer nanocomposites. An overview of the main results on this topic is presented together with an introduction to the basic concepts relating to X-ray photon correlation spectroscopy, neutron backscattering, and neutron spin echo measurements.

Recent scattering approaches to structure and dynamics of polymer nanocomposites

“…The thermal stiffening effect can be used in devices that require high modulus and high viscosity under the oscillating shear application. Viscosity reduction was observed by scattering methods on fluidification of the nanocomposites through the addition of small NPs (Senses et al, 2022b).…”

“…On the other hand, scattering approaches are usually non-destructive, and by finely observing changes in wave vector and energy of X-rays or neutrons shining through samples, it is possible to conclude on the microstructure and dynamics on the nanoscale. For polymer nanocomposites, both approaches have been used and sometimes combined to access information on either the polymer chains or the filler nanoparticles (Bailey and Winey (2020); Genix and Oberdisse (2015); Senses et al (2022a)). In this mini-review, we focus on a few recent approaches to filler microstructure by small-angle scattering (of X-rays, SAXS or neutrons, and SANS, respectively) in the first subsection and on the dynamical properties of polymer chains, either in bulk or at interfaces, in the second subsection, using quasi-elastic neutron scattering (QENS), sometimes complemented by broadband dielectric spectroscopy (BDS).…”

Scaling Perspective on Dynamics of Nanoparticles in Polymers: Length- and Time-Scale Dependent Nanoparticle–Polymer Coupling

“…Also excluded are the effects of nanoparticles on the dynamics of the polymer matrix as well as on the dynamics and rheology of the polymer nanocomposite as a whole. Readers interested in the excluded topics are advised to read relevant research and review articles. ,− …”

The effect of dynamically heterogeneous interphases on the particle dynamics of polymer nanocomposites

“…The dynamics of nanoparticles in polymers contributes to our understanding of the viscosity changes and reinforcement origin of nanocomposites, and of the relaxations of host polymers depending on particle-polymer interactions. 16,[24][25][26][27][28][29] X-ray photon correlation spectroscopy (XPCS) probes nanoparticle dynamics in viscoelastic media, and directly measures nanoparticle relaxations in the highly entangled polymer melt. [30][31][32][33] An entanglement controlled environment such as the high-molecular-weight solutions was shown to dictate the temporal fluctuations of the entanglement mesh.…”