Dynamics in dense hard-sphere colloidal suspensions

Abstract

The dynamic behavior of a hard-sphere colloidal suspension was studied by X-ray Photon Correlation Spectroscopy and Small Angle X-ray Scattering over a wide range of particle volume fractions. The short-time mobility of the particles was found to be smaller than that of free particles even at relatively low concentrations, showing the importance of indirect hydrodynamic interactions. Hydrodynamic functions were derived from the data and for moderate particle volume fractions (Φ ≤ 0.40) there is a good agreement with earlier many-body theory calculations by Beenakker and Mazur [C.W.J. Beenakker and P. Mazur, Physica A 120, 349 (1984)]. Important discrepancies appear at higher concentrations, above Φ ≈ 0.40, where the hydrodynamic effects are overestimated by the Beenakker-Mazur theory, but predicted accurately by an accelerated Stokesian dynamics algorithm developed by Banchio and Brady [A.J. Banchio and J. F. Brady, J. Chem. Phys. 118, 10323 (2003)]. For the relaxation rates, good agreement was also found between the experimental data and a scaling form predicted by Mode Coupling Theory. In the high concentration range, with the fluid suspensions approaching the glass transition, the long-time diffusion coefficient was compared with the short-time collective diffusion coefficient to verify a scaling relation previously proposed by Segrè and Pusey [P.N. Segrè and P.N. Pusey, Phys. Rev. Lett. 77, 771 (1996)]. We discuss our results in view of previous experimental attempts to validate this scaling law [L. Lurio et al., Phys. Rev. Lett. 84, 785 (2000)].

Dynamics of a model colloidal suspension from dilute to freezing

“…al. [27]. The multiexponential analysis procedure that we performed on our data allows the contributions from the individual terms in Eq.…”

“…They were able to see the scaling behavior over several decades in time but not in the long time limit. More recent work by Orsi et al [27] studied a system very similar to that used by Martinez and Segrè, and found that the scaling law did hold for high concentration sterically stabilized colloids.…”

“…In the liquid state, the empirical fit to the intermediate scattering function usually takes the form of a single or double exponential [26,27]. In extremely dilute systems at low wavevector, DLS yields a single exponential decay with a wavevector independent diffusion coefficient.…”

“…At moderate packing fractions, a second decay mode is observed and the data is fitted with two exponentials with different effective diffusion coefficients [9,27]. These two empirical modes are often associated with short-time and long-time diffusion coefficients, where the former is associated with movement of the colloidal particles in its local cage while the latter is associated with diffusion over larger length scales [9].…”

Stress relaxation in quasi-two-dimensional self-assembled nanoparticle monolayers

“…Along with the ability to study in situ dynamics came the capacity to observe processes such as glass formation, relaxation, collective dynamics, and jamming in real time [7,[35][36][37]. Recently, X-ray Photon Correlation Spectroscopy (XPCS) has been used to study the diffusion and hydrodynamic interactions of 2D gel systems composed of disordered nanoparticle assemblies at the air-water interface [38][39][40].…”