Nanoparticle Motion within Glassy Polymer Melts

Abstract

X-ray photon correlation spectroscopy is employed to investigate the motion of dilute suspensions of gold nanoparticles in low-molecular-weight polystyrene melts. At high temperatures, the observed motion is diffusive, with a rate that follows a Vogel-Fulcher temperature dependence. Closer to the glass transition temperature Tg, diffusion is superseded by a hyperdiffusive process that first becomes observable near a crossover temperature Tc approximately 1.1Tg and is identified with heterogeneous strain in the melts. Following rapid cooling to temperatures sufficiently below Tc, but still above Tg, the hyperdiffusive dynamics displays a time dependence similar to aging in polymer glasses.

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

“…On the other 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 F o r P e e r R e v i e w O n l y hand, the KWW exponent γ is q-independent and close to 1.5 (right panel). These results are very similar to what we recently measured in a XPCS experiment on multilayers of pure PA4 [9], suggesting that the dynamics of nanoparticles can be used to investigate the internal dynamics of the polymer, in analogy with previous measurements on glassy polymer melts [3]. This is particularly true given that the GNP concentration is low enough to leave the mechanical properties of the polymer unaffected [20][21][22].…”

“…On the other hand, stabilized nanoparticles at low volume fraction may be considered as passive tracers of the superdiffusive microscopic bulk dynamics observed in low-molecular-weight polymer melts [3] and in supercooled liquids near the glass transition [4].…”

Compressed correlation functions and fast aging dynamics in metallic glasses

“…23,26 This interpretation suggests the existence of a different kind of dynamics, rather than pure diffusion, in metallic glasses, which display many similarities with that of out-of-equilibrium soft materials, such as concentrated colloidal suspensions and nanoparticle probes in a glass former matrix. 23,[39][40][41][42] In the case of Zr 67 Ni 33 the shape parameter is even larger than the one reported for Mg 65 Cu 25 Y 10 (β ∼ 1.5 for a similar thermal path). This may suggest the presence of larger atomic mobility or more internal stresses in Zr 67 Ni 33 , a conclusion which however requires further investigations.…”

Beyond simple exponential correlation functions and equilibrium dynamics in x-ray photon correlation spectroscopy

“…An accompanying feature of these dynamics is a relaxation rate that varies approximately linearly with wave vector, ∼ Q, implying hyper-diffusive, convectivelike motion. The wide assortment of disordered soft materials displaying these dynamics, as well as their observation with XPCS in a variety of polymeric systems [40]- [47] and in colloidal motion in glassy solvents [46,48,49], suggests a generic underlying mechanism; however, no clear consensus about their microscopic origin has emerged. As mentioned above, the continuous time Lévy flight model with a power-law distribution of waiting times can account for equation (8) with either γ < 1 or γ > 1.…”