Cooperative activated dynamics in dense mixtures of hard and sticky spheres.
ABSTRACT The coupled activated dynamics in dense mixtures of repulsive and sticky hard spheres is studied using stochastic nonlinear Langevin equation theory. The effective free energy surface, barriers, saddle point trajectories, and mean first passage times depend in a rich manner on mixture composition, (high) total volume fraction, and attractive interaction strength. In general, there are three types of saddle point trajectories or relaxation pathways: a pure sticky or pure repulsive particle displacement keeping the other species localized, and a cooperative motion involving repulsive and attractive particle displacements. The barrier for activated hopping usually increases with the ratio of sticky to repulsive particle displacement. However, at intermediate values of the displacement ratio it can attain a broad plateau value, and can even exhibit a local maximum, and hence nonmonotonic behavior, at high sticky particle mixture compositions if the attraction strength is modest. The mean first passage, or hopping, times are computed using multidimensional Kramers theory. In most cases the hopping time trends reflect the behavior of the barrier height, especially as the sticky particle attraction strengths become large. However, there are dramatic exceptions associated with cooperative repulsive and attractive particle trajectories where the barriers are high but a greatly enhanced number of such trajectories exist near the saddle point.
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ABSTRACT: Depletion forces are accounted for by a contraction of the description of colloidal mixtures based on the integral equations theory of simple liquids. The applicability of this treatment is illustrated for binary mixtures of hard spheres, in the bulk and near a hard wall. The Asakura and Oosawa potential is obtained as the dilute limit of our equations. At higher concentrations the depletion potential has an oscillatory behavior and becomes more long ranged. If charge is put on the small particles there are energy-driven depletion forces in addition to those of entropic origin, which result in repulsive interaction at contact.Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 05/2000; 61(4 Pt B):4095-9.
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ABSTRACT: The transition from a liquid to a glass in colloidal suspensions of particles interacting through a hard core plus an attractive square-well potential is studied within the mode-coupling-theory framework. When the width of the attractive potential is much shorter than the hard-core diameter, a reentrant behavior of the liquid-glass line and a glass-glass-transition line are found in the temperature-density plane of the model. For small well-width values, the glass-glass-transition line terminates in a third-order bifurcation point, i.e., in a A3 (cusp) singularity. On increasing the square-well width, the glass-glass line disappears, giving rise to a fourth-order A4 (swallow-tail) singularity at a critical well width. Close to the A3 and A4 singularities the decay of the density correlators shows stretching of huge dynamical windows, in particular logarithmic time dependence.Physical Review E 02/2001; 63(1 Pt 1):011401. · 2.31 Impact Factor
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ABSTRACT: We derive an extension of the mode-coupling theory for the liquid-glass transition to a class of models of confined fluids, where the fluid particles evolve in a disordered array of interaction sites. We find that the corresponding equations are similar to those describing the bulk, implying that the methods of investigation which were developed there are directly transferable to this new domain of application. We then compute the dynamical phase diagram of a simple model system and show that new and nontrivial transition scenarios, including reentrant glass transitions and higher-order singularities, can be predicted from the proposed theory.Physical Review Letters 03/2005; 94(6):065703. · 7.94 Impact Factor