Multiscale Dynamics of Polymers in Particle-Rich Nanocomposites

作者：Mangal Rahul; Wen Yu Ho; Choudhury Snehashis; Archer Lynden A^*

来源：Macromolecules, 2016, 49(14): 5202-5212.

DOI：10.1021/acs.macromol.6b00496

We report on the dynamics of entangled polymers in polymer-nanoparticle composites (PNCs) with moderate and high particle loadings. Using composites comprised of poly(ethylene glycol) (PEG)-tethered silica (SiO2) nanoparticles and poly(methyl methacrylate) (PMMA), we show by means of small-angle X-ray scattering (SAXS) analysis that the nanoparticles are uniformly dispersed over a range of particle concentrations. From oscillatory shear rheology measurements, we find that the time temperature superposition (TTS) principle holds for these SiO2-PEG/PMMA PNCs up to a particle concentration phi(G) approximate to 11% where the materials begin to exhibit soft glassy rheological properties. At particle concentrations below phi(G), we take advantage of TTS to create dynamic maps for PNCs that span time scales ranging from fast segmental motions to slow terminal relaxation of polymer chains. These maps reveal that at low phi and depending on the host polymer (PMMA) molecular weight (M-w), hairy nanoparticles may either speed up or slow down terminal relaxation of the host. In contrast, at high phi, nanoparticles slow down polymer dynamics on intermediate and long time scales, irrespective of the host polymer M-w. The slowdown coincides with particle concentrations at which the mean interparticle spacing lies below the equilibrium tube diameter of the entangled PMMA host and is thought to reflect the onset of confinement dynamics of polymer chains in PNCs. Studies of PNCs in the confinement regime reveal important analogies between glassy attributes of 3D-confined polymer chains in nanocomposites with those of polymer thin films supported on attractive substrates.

• 出版日期2016-7-26