Dynamics of Nanoparticles in a Supercooled Liquid

Abstract

The dynamic properties of nanoparticles suspended in a supercooled glass forming liquid are studied by x-ray photon correlation spectroscopy. While at high temperatures the particles undergo Brownian motion the measurements closer to the glass transition indicate hyperdiffusive behavior. In this state the dynamics is independent of the local structural arrangement of nanoparticles, suggesting a cooperative behavior governed by the near-vitreous solvent.

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

“…However, the strongly nonexponential character of the relaxations persists as characterized by highly compressed decays and an approximately linear relationship between Q and (figure 2). This is rather similar to the observations in [48], where non-exponential relaxations and Q ∝ behavior were observed in a system (nano-particles in a supercooled glass-forming solvent) without any visible ageing of the dynamics. In contrast to [48], here we observe almost no dispersion of γ , which remains very close to 2 in the investigated Q-range for this aerogel.…”

“…This is rather similar to the observations in [48], where non-exponential relaxations and Q ∝ behavior were observed in a system (nano-particles in a supercooled glass-forming solvent) without any visible ageing of the dynamics. In contrast to [48], here we observe almost no dispersion of γ , which remains very close to 2 in the investigated Q-range for this aerogel. This points towards a length scale δ of characteristic jumps that would be very small (upper limit: δ 0.1/Q max = 0.5 nm) if these data were to be modeled within the continuous time random walk (CTRW) model assuming Gaussian jumps to account for γ = 2.…”

“…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. Support for this model in describing the observed hyper-diffusive motion comes from several systems for which γ has a Q-dependence that is accurately captured by the model [31,48]. Another explanation for the hyper-diffusive dynamics invokes a process of stress relaxation in which point-dipole stress fields create a distribution of strain velocities [27].…”

“…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.…”

Surface and Interface Analyses of Polymer Brushes by Synchrotron Radiation

“…Various detectors have been used and developed. Up to now, considerable numbers of experiments have been conducted with various types of 2D detectors, such as the directly illuminated X-ray CCD, 49) the indirectly illuminated X-ray CCD, 50) and photon counting 2D detectors such as Medipix2 detector, 51) the PILATUS detector 52) and Maxipix detector. 53) The correlation functions mentioned above are taken by homodyne experiments, thus the phase information of the scattered electric fields are lost.…”