Slow dynamics of supercooled colloidal fluids: spatial heterogeneities and nonequilibrium density fluctuations

M. Tokuyama, Y. Enomoto and I. Oppenheim

Physica A: Statistical Mechanics and its Applications, 1999, vol. 270, issue 3, 380-402

Abstract: The coupled diffusion equations recently proposed by Tokuyama for concentrated hard-sphere suspensions are numerically solved, starting from nonequilibrium initial configurations. The most important feature of those equations is that the self-diffusion coefficient DS(Φ) becomes zero at the glass transition volume fraction φg as DS(Φ)∼D0|1−Φ(x,t)/φg|γ with γ=2 where Φ(x,t) is the local volume fraction of colloids, D0 the single-particle diffusion constant, and φg=(43)3/(7ln3−8ln2+2). This dynamic anomaly results from the many-body correlations due to the long-range hydrodynamic interactions. Then, it is shown how small initial disturbances can be enhanced by this anomaly near φg, leading to long-lived, spatial heterogeneities. Those heterogeneities are responsible for the slow relaxation of nonequilibrium density fluctuations. In fact, the self-intermediate scattering function is shown to obey a two-step relaxation around the β-relaxation time tβ∼|1−φ/φg|−1, and also to be well approximated by the Kohlrausch–Williams–Watts function with an exponent β around the α-relaxation time tα∼|1−φ/φg|−η, where η=γ/β, and φ is the particle volume fraction. Thus, the nonexponential α relaxation is shown to be explained by the existence of long-lived, spatial heterogeneities.

Keywords: Dynamic anomaly; Hard-sphere suspensions; Nonequilibrium density fluctuations; Slow dynamics; Spatial heterogeneities (search for similar items in EconPapers)
Date: 1999
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Persistent link: https://EconPapers.repec.org/RePEc:eee:phsmap:v:270:y:1999:i:3:p:380-402

DOI: 10.1016/S0378-4371(99)00172-7

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