Reduced-mobility layers with high internal mobility in poly(ethylene oxide)–silica nanocomposites

Abstract

A series of poly(ethylene oxide) nanocomposites with spherical silica was studied by proton NMR spectroscopy, identifying and characterizing reduced-mobility components arising from either roomtemperature lateral adsorption or possibly end-group mediated high-temperature bonding to the silica surface. The study complements earlier neutron-scattering results for some of the samples. The estimated thickness of a layer characterized by significant internal mobility resembling backbone rotation ranges from 2 nm for longer (20 k) chains adsorbed on 42 nm diameter particles to 0.5 nm and below for shorter (2 k) chains on 13 nm particles. In the latter case, even lower adsorbed amounts are found when hydroxy endgroups are replaced by methyl endgroups. Both heating and water addition do not lead to significant changes of the observables, in contrast to other systems such as acrylate polymers adsorbed to silica, where temperature-and solvent-induced softening associated with a glass transition temperature gradient was evidenced. We highlight the actual agreement and complementarity of NMR and neutron scattering results, with the earlier ambiguities mainly arising from different sensitivities to the component fractions and the details of their mobility.

Nanoscale Particle Motion in Attractive Polymer Nanocomposites

“…Most of the proposed reinforcement mechanisms in attractive PNCs are primarily based on modification of the polymer mobility [27][28][29]; however, it is quite difficult to separate the dynamical processes of the highly interacting matrix and of the interfacial chains. Meanwhile, the NPs essentially reflect the local viscoelastic properties of polymer in their nanoscale motion that is commonly measured by x-ray photon correlation spectroscopy (XPCS) [30][31][32][33].…”

Influence of the morphological structure of carbon nanotubes on the viscoelasticity of PMMA‐based nanocomposites

“…corrects the somewhat of the formula in Ref. by simply multiplying a surface area ratio, where a formula was proposed for sphere particles. With the increase of temperature, the reduced‐mobility fraction of α i decreases.…”

“…With a thin MMA layer, the CNTs disperse within matrix and combine with matrix through bonded segments which form a low viscosity layer [Figure (d)]. Such layer of bonded segments presented around CNTs with more regular arrangement, which was named “glassy layer” . When higher ambient pressure was applied on this melt, lower compressibility was observed than those without such features (i.e., CNTs‐2).…”

“…Such layer of bonded segments presented around CNTs with more regular arrangement, which was named "glassy layer". [42][43][44] When higher ambient pressure was applied on this melt, lower compressibility was observed than those without such features (i.e., CNTs-2). Therefore, as discussed above, such coated layer effectively increases the interfacial layer thickness, causing a decrease on the viscosity.…”

Rubber-Filler Interactions in Polyisoprene Filled with In Situ Generated Silica: A Solid State NMR Study

“…1 H low-resolution solid state NMR has been widely used to characterize polymer-filler composites [6,10,11,12,13,14,15,16,17,18,19,20,21]. In particular, spin-spin relaxation times ( T 2 ) are usually exploited to investigate polymer-filler interactions and the formation of bound rubber, while spin-lattice relaxation times in the laboratory ( T 1 ) and the rotating ( T 1 ρ ) frame can give insights into polymer motions (typically segmental motions above T g ) occurring in the MHz and kHz regimes, respectively.…”