Structure and Dynamics Studies of Concentrated Micrometer-Sized Colloidal Suspensions

Abstract

We present an experimental study of the structural and dynamical properties of concentrated suspensions of different sized polystyrene microspheres dispersed in glycerol for volume fraction concentrations between 10% and 20%. The static structure, probed with ultrasmall-angle X-ray scattering, shows a behavior very similar to that of hard spheres. The equilibrium dynamics is probed with ultrasmall-angle X-ray scattering-X-ray photon correlation spectroscopy, a new technique that overcomes the limits of visible light-scattering techniques imposed by multiple scattering and is suitable for studies of optically opaque materials containing micrometer-sized structures. We found that the intensity autocorrelation functions are better described by a stretched exponential function and microspheres in a concentrated suspension move collectively. We also found that the inverse of the effective diffusion coefficients displays a peak with respect to the scattering vector that resembles the peaks in the static structure factors, which indicates that a long-lived, low free-energy state exists. The relaxation time is approximately inversely related to scattering vector, a behavior consistent with models that describe the dynamics in terms of random, local structural arrangements in disordered media.

Structure and Dynamics of Bimodal Colloidal Dispersions in a Low-Molecular-Weight Polymer Solution

“…We further assumed that the partial structure factor S 11 ( q ), S 12 ( q ), and S 22 ( q ) for monodisperse particles can be reasonably approximated for particles with narrow size distributions, which is a widely accepted practice. 23, 69, 74 For our analysis, we adopted a simplest approach, where our model (Eqn. (3)) only includes the volume fractions of the large and small species, as well as a normalization factor that accounts for the uncertainties in the sample thickness.…”

Simultaneous multiplexed materials characterization using a high-precision hard X-ray micro-slit array

“…We have previously shown that this normalization does not affect the measured dynamics (Zhang et al, 2011). The relaxation time represented by the calculated intensity autocorrelation function was further analyzed by modeling the autocorrelation function with a stretched exponential form [also known as the Kohlrausch-Williams-Watts (KWW) function (Caronna et al, 2008;Madsen et al, 2010;Zhang et al, 2013)]. It is defined as…”

“…For the multiplexed USAXS-XPCS measurements here, the multi-slit array comprised four of the five narrower (15 mm wide) bottom slits shown, with the USAXS entrance slit vertical aperture set to 50 mm to define the slit height. brium dynamics and revealing the q-dependence of the relaxation time scales (Zhang et al, 2013). USAXS-XPCS in the scan mode can serve as a structural probe to study the time scales associated with non-equilibrium dynamics in materials under various conditions pertinent to material performance (Zhang, Allen, Levine, Espinal et al, 2012;Zhang et al, 2014).…”

“…Over the past two decades, XPCS has not only led to significant progress in our understanding of a wide variety of important dynamic phenomena but has also shown great potential for impacting many areas of statistical physics. Prominent examples include studies of concentrated colloidal suspensions (Lurio et al, 2000;Orsi et al, 2012;Zhang et al, 2013), glassy dynamics (Robert et al, 2006;Guo et al, 2009), atomic diffusion (Leitner et al, 2009;Ruta et al, 2012) and dynamical heterogeneities in soft matter (Trappe et al, 2007;Guo et al, 2011). Despite these successes, XPCS is severely constrained by the lack of coherent flux from a third-generation synchrotron source.…”

Small-Angle X-Ray Scattering of Ionic Liquids

“…Research areas that have benefitted considerably from XPCS include but are not limited to equilibrium dynamics of concentrated colloidal suspensions [90][91][92][93][94][95], glassy dynamics [96,97], atomic diffusion [98,99], dynamical heterogeneities in soft matter [100,101], critical fluctuations of liquid crystals [102,103], near-equilibrium coarsening fluctuation in alloys [104] and weakly disturbed soft condensed matter systems [96,[105][106][107], and surface dynamics of fluidic and polymeric systems [108][109][110][111][112][113][114]. Most of these systems share some common traits, namely, the dynamical fluctuations happen on a length scale between nanometers and micrometers, and the dynamic timescale is greater than a microsecond.…”