Influence of molecular weight on the distribution of segmental relaxation in polymer grafted nanoparticles

The segmental dynamics of one-component nanocomposites (OCNC) is significantly influenced by the molecular weight $\left(M_w\right)$ of the grafted polymer. Neutron backscattering shows that compared to the neat polymer the OCNCs exhibit a shift from slower segmental dynamics at low $M_w$ to faster dynamics at high $M_w$. We model the local relaxation as distribution of exponential diffusers. This approach reveals the presence of fast and slow segments in both OCNCs. However, their fractional contribution varies with $M_w$ leading to different average relaxation times. Our results present important insights into the origin of segmental mobility in OCNC and address the inconsistencies in different literature reports.

Figure 1

Fitted backscattering spectra for polyisoprene, $5000\mathrm{g}/\mathrm{mole}$ and its nanocomposite obtained at 300 K and $Q=1.12{\AA }^1$. Inset shows relaxation times from PI-5k and NC-5k at 275 and 300 K for different $Q$.

Figure 2

Fitted backscattering spectra for polyisoprene, $12000\mathrm{g}/\mathrm{mole}$ and its nanocomposite obtained at 300 K and $Q=1.12{\AA }^1$. Inset shows relaxation times from PI-12k and NC-12k at 275 and 300 K for different $Q$.

Figure 3

Comparison of relaxation time spectra for PI-5k, NC-5k, PI-12k, and NC-12k at 300 K from (a) backscattering at $Q=1.4{\AA }^1$, (b) dielectric spectroscopy, and (c) vertically shifted backscattering data at 300 K and $Q=1.4{\AA }^1$. The black lines indicate the data description on the basis of the shifted dielectric relaxation time spectra.