Resolving Segmental Polymer Dynamics in Nanocomposites by Incoherent Neutron Spin–Echo Spectroscopy

Abstract

The segmental dynamics of styrene-butadiene nanocomposites with embedded silica nanoparticles (NPs, ca. 20%v) has been studied by broadband dielectric (BDS) and neutron spin-echo spectroscopy (NSE). It is shown by BDS that overlapping contributions only allow to conclude on a range of distributions of relaxation times in simplified industrial nanocomposites formed with highly polydisperse NPs. For comparison, structurally similar but less aggregated colloidal nanocomposites have a well-defined distribution of relaxation times due to the reduced influence of interfacial polarization processes. This distribution is widened with respect to the neat polymer, without change in the position of the maximum, and at most a small slowing down visible in the average time. We then demonstrate that incoherent NSE can be used to resolve small modifications of segmental dynamics of the industrial samples. By carefully choosing the q-vector of the measurement, experiments with fully hydrogenated polymer give access to the self-dynamics of the polymer in the presence of silica on the scale of approximately 1 nm. Our high resolution measurements show that the segmental motion is slightly but systematically slowed down also by the presence of the industrial filler NPs.

Partition of Coating Agents between Nanoparticle Interfaces and the Polymer in Nanocomposites

“…It is also clear from Figure 2 (together with Table 1) that this factor increases with increasing silica content, meaning that more coating agent accumulates in the matrix, presumably due to the overall increasing silane concentration which is added at fixed mass ratio with respect to the NPs. Finally, in absence of coating agent ("bare" sample in Figure 5b), the τmax of the segmental dynamics is found to change only marginally (see also 21 ), confirming the much stronger role of the silanes in the matrix with respect to any possible impact of the silica content on τmax, as discussed previously. In parallel, the shape of the time distribution was hardly changed with respect to pure SB (w = 0.32, resp.…”

“…We have shown recently that the position of the maximum of the time distribution associated with the α-relaxation is only marginally sensitive to the presence of the nanoparticles in this system. 21 There, In PNCs, due to the presence of MWS processes in the low-frequency regime, high temperatures have…”

“…We have shown recently that the position of the maximum of the time distribution associated with the α-relaxation is only marginally sensitive to the presence of the nanoparticles in this system. 21 In PNCs, due to the presence of MWS processes in the low-frequency regime, high temperatures have to be investigated first. Describing the MWS contribution allows isolating the -process of relevance for the present study, the position of which is well defined in the frequency window at 258 K for all PNCs.…”

“…In this case, the overall segmental dynamics evaluated by means of the apparent peak maximum in the dielectric spectra is shifted toward longer time scales and a decrease in the calorimetric T g is observed. 26 In typical rubber systems, like the one studied here, however, enthalpic interactions between the polymer segment and the NP surface (hydroxyl groups) are weak and the influence of the interfacial polymer layer is extremely low, as shown by incoherent neutron spin-echo 21 or low-field NMR experiments. 27,28 In the latter, at most, a few percent of the immobilized polymer forming nanometer-thick shells may be identified.…”

Direct Structural Evidence for Interfacial Gradients in Asymmetric Polymer Nanocomposite Blends

“…In order to highlight the polymer contribution using the ZAC-technique, PNC samples have been designed in such a way that the average contrast of the silica NPs is always zero 10,12 ΔρNP = ρNP -ρmat = ρNP -(H ρH + D ρD) = 0 (5) with the chain volume fractions obeying H + D = 1. For the two silica beads, H is found to be ca.…”