Decoupling the Polymer Dynamics and the Nanoparticle Network Dynamics of Polymer Nanocomposites through Dielectric Spectroscopy and Rheology

Abstract

The dynamics of polymer nanocomposites (PNCs) are dictated by two intertwining components, the polymer matrix and the nanoparticle network, whose characteristics have not been elucidated. Here, we unravel the salient features of the polymer matrix dynamics and the nanoparticle network dynamics through dielectric spectroscopy and rheology. Dielectric measurements show that the dynamics of the polymer matrix of PNCs are almost identical to that of the neat polymer. In contrast, rheological measurements exhibit a strong deviation in the dynamics of PNCs from that of the neat polymer. Detailed analyses show that the rheology captures both contributions of the polymer matrix and the nanoparticle network while dielectric measurements are only sensitive to polymer matrix dynamics. Moreover, the dynamics of the polymer matrix and the nanoparticle network have very different temperature dependences, leading to a dynamic decoupling phenomenon and the breakdown of the time–temperature superposition principle in PNCs.

Collective Nanoparticle Dynamics Associated with Bridging Network Formation in Model Polymer Nanocomposites

“…The results in Figure suggest that this four-dimensional function may factorize, to leading order, into a product of a q - and ϕ-dependent function (reflecting polymer-mediated NP collective dynamics) that is independent of chain length to leading order, multiplied by a T - and M w -dependent function that sets an elementary time scale associated with friction on NPs due to the dynamics of the polymer matrix. If the polymer subsystem dynamics was unperturbed by NPs from the segmental to chain scales, as suggested by recent ensemble-average dielectric measurements, then this elementary time scale would be proportional to the SE time discussed above, τ SE , computed using the pure polymer melt viscosity. Moreover, if the polymer dynamics was fast (effectively equilibrated) compared to the collective NP motions probed in the experiments (as suggested by a recent combined viscoelastic and dielectric experimental study), then, at least in an average sense, polymers influence collective NP dynamics in two ways: (i) modify their equilibrium microstructure ( e .…”

“…If the polymer subsystem dynamics was unperturbed by NPs from the segmental to chain scales, as suggested by recent ensemble-average dielectric measurements, then this elementary time scale would be proportional to the SE time discussed above, τ SE , computed using the pure polymer melt viscosity. Moreover, if the polymer dynamics was fast (effectively equilibrated) compared to the collective NP motions probed in the experiments (as suggested by a recent combined viscoelastic and dielectric experimental study), then, at least in an average sense, polymers influence collective NP dynamics in two ways: (i) modify their equilibrium microstructure ( e . g ., bridges, adsorbed layers) as embedded in S ( q ), and (ii) set the elementary time scale we define as τ 0 associated via the friction they exert on a NP.…”

“…A simple interpretation of Δ E is it reflects the activation energy for bridging polymer desorption per chain, and μ­( T ) and R are a temperature-dependent numerical constant and the gas constant, respectively. Motivated by such concepts, Cheng and co-workers demonstrated that the shift factors of SiO 2 filled PNCs from oscillatory shear rheology follow: where T ref is the reference temperature and a 0 ( T ) is the dielectric shift factor which in the PNC was essentially identical to that in the pure polymer melt. The Boltzmann factor is meant to model in a simple manner the dissociation or dynamical breakup of the local structure associated with NP-polymer bridges which controls the lower frequency rheological properties of the PNCs.…”

Interface Structure and Dynamics in Polymer‐Nanoparticle Hybrids: A Review on Molecular Mechanisms Underlying the Improved Interfaces

“…highlight that the polymer chains in the neighbourhood of nanoparticles inevitably undergo the structural and dynamical perturbations triggered by NPs. As depicted in Scheme 1 these perturbations are attributes to the existence of an interfacial layer ( l int ) with few nm thicknesses in the vicinity of NP surface and demonstrated as peaks of enhanced density, bond orientation, and restrained atom mobility leading to changes in thermal and viscoelastic properties of the PNCs [39–76] . (Carroll et al., 2017; Klonos et al., and Klonos et al., 2017).…”

“…Regardless of all the substantial insights and also the difficulty in the experimental characterization of the interface region, in many cases, large scattering and conflicting results reported in the literature prevent the drawing of firm conclusions [39–76] . Hence, computational techniques, especially atomistic simulations, are needed to characterize the matrix filler, interfacial interactions.…”