Colloidal glasses

E. R. Weeks, J. C. Crocker, A. C. Levitt, A. Schofield, and D. A. Weitz, Three-dimensional direct imaging of structural relaxation near the colloidal glass transition. Science 287, 627-631 (2000). 

R. E. Courtland and E. R. Weeks, Direct visuahzation of ageing in colloidal glasses. J. Phys. (Condensed Matter) 15, S359-S365 (2003). 

In Section VI, we consider a classical particle diffusing in an out-of-equilibrium environment. In this case, all the dynamical variables attached to the particle, even its velocity, are aging variables. We analyze how the drift and diffusion properties of the particle can be interpreted in terms of an effective temperature of the medium. From an experimental point of view, independent measurements of the mean-square displacement and of the mobility of a particle immersed in an aging medium such as a colloidal glass give access to an out-of-equilibrium generalized Stokes-Einstein relation, from which the effective temperature of the medium can eventually be deduced. 

Experimentally, the effective temperature of a colloidal glass can be determined by studying the anomalous drift and diffusion properties of an immersed probe particle. More precisely, one measures, at the same age of the medium, on the one hand, the particle mean-square displacement as a function of time, and, on the other hand, its frequency-dependent mobility. This program has recently been achieved for a micrometric bead immersed in a glassy colloidal suspension of Laponite. As a result, both Ax2(t) and p(co) are found to display power-law behaviors in the experimental range of measurements [12]. 

B. Abou and F. Gallet, Probing a nonequilibrium Einstein relation in an aging colloidal glass. Phys. Rev. Lett. 93, 160603 (2004). 

Keywords Colloidal dispersions Colloidal glasses Dynamics Grafted particles Hairy particles Micelles Nanoparticle-polymer hybrids Phase diagrams Polymers Rheology Soft colloids- Softness Stars... 

Fig. 18 Schematic representation of crowded soft systems (a) entangled polymers, (b) repulsive colloidal hard spheres, (c) colloidal star polymers, and (d) attractive hard spheres. The former are described by the tube model for entanglements, whereas the latter three by the general cage model for colloidal glasses...

A very rich rheological response characterizes colloidal glasses and can serve as a means of identifying and/or distinguishing their different kinds [22,252-255]. 

The outline of the review is as follows. First the microscopic starting points, the formally exact manipulations, and the central approximations of MCT-ITT are described in detail. Section 3 summarizes the predictions for the viscoelasticity in the linear response regime and their recent experimental tests. These tests are the quantitatively most stringent ones, because the theory can be evaluated without technical approximations in the linear limit important parameters are also introduced here. Section 4 is central to the review, as it discusses the universal scenario of a glass transition under shear. The shear melting of colloidal glasses and the key physical mechanisms behind the structural relaxation in flow are described. Section 5 builds on the insights in the universal aspects and formulates successively simpler models which are amenable to complete quantitative analysis. In the next section. 

The loss modulus rises again at very low frequencies, which may indicate that the colloidal glass... 

Fig. 10 Glass form factors fq as function of wavevector q in a colloidal glass of hard spheres for packing fractions as labeled. Data obtained by van Megen and coworkers by dynamic light scattering are qualitatively compared to MCT computations using the PY-5j at values chosen ad hoc to match the experimental data from [12]. The PY structure factor at the glass transition density = 0.58 is shown as broken line, rescaled by a factor 1/10...

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