The thermomechanical responses of polymers, which provide limitations to their practical use, are favourably altered by the addition of trace amounts of a nanofiller. However, the resulting changes in polymer properties are poorly understood, primarily due to the non-uniform spatial distribution of nanoparticles. Here we show that the thermomechanical properties of 'polymer nanocomposites' are quantitatively equivalent to the well-documented case of planar polymer films. We quantify this equivalence by drawing a direct analogy between film thickness and an appropriate experimental interparticle spacing. We show that the changes in glass-transition temperature with decreasing interparticle spacing for two filler surface treatments are quantitatively equivalent to the corresponding thin-film data with a non-wetting and a wetting polymer-particle interface. Our results offer new insights into the role of confinement on the glass transition, and we conclude that the mere presence of regions of modified mobility in the vicinity of the particle surfaces, that is, a simple two-layer model, is insufficient to explain our results. Rather, we conjecture that the glass-transition process requires that the interphase regions surrounding different particles interact.

We show that the thermomechanical properties of polymer nanocomposites are critically affected by polymer-particle wetting behavior. Silica nanoparticles grafted with dense polystyrene brushes of degree of polymerization 1050 are blended with polystyrene melts to form nanocomposites. It was found that low molecular weight (MW) polystyrene melts with lengths <880 wet these particles. Concurrently, the glass transition temperature (T g ) of the nanocomposite increases. At higher MW, the matrix does not wet the particles and the T g decreases.

The one-orbital model for manganites with cooperative phonons and superexchange coupling JAF is investigated via large-scale Monte Carlo simulations. The results for two orbitals are also briefly discussed. Focusing on the electron density n=0.75, a regime of competition between ferromagnetic metallic and charge-ordered (CO) insulating states is identified. In the vicinity of the associated bicritical point, colossal magnetoresistance (CMR) effects are observed. The CMR is associated with the development of short-distance correlations among polarons, above the spin ordering temperatures, resembling the charge arrangement of the low-temperature CO state.

A small amount of alumina nanoparticles in polymethylmethacrylate causes a sharp depression of the glass transition temperature (Tg) accompanied by a toughening of the composite. We investigated this phenomenon using multispeckle x-ray photon correlation spectroscopy. Measurements reveal a dynamic structure factor that has the form exp[-(t/taua)beta], with beta greater than 1. We show for the first time that beta(T) tracks the internal stress at the polymer-particle interface. The internal stress, which we propose arises due to the entropic penalty that the polymer faces in the presence of the nanoparticles, engenders temporally heterogeneous dynamics. In the jammed glassy state, we show that the dominant fast relaxation mode--taumax--aided by a weak dewetting interface relieves the stress and follows the variations in Tg.