Localization and glass formation of fluids confined in porous matrices

1. Introduction Recently, the dynamics of colloids in porous media has been subject to a number of works. The slow dynamics is of particular interest, since the single-particle (" self ") and the collective dynamics are influenced by the intricate interplay between confinement and connectivity of the surrounding medium. Recently, Krakoviack [1–3] combined mode-coupling theory (MCT) [4] with the replica Ornstein-Zernike (ROZ) formalism [5]. The resulting theory describes the glass formation process of a quenched-annealed (QA) mixture, i.e. of systems in which mobile fluid particles move in a matrix of immobile particles quenched from an equilibrium fluid. Based on the static structure factors of the system, the theory predicts the time dependence of the self and the (connected) collective intermediate scattering functions F s (k,t) and F c (k,t). The kinetic diagram of a simple hard sphere (HS) fluid in a HS matrix, evaluated using this new theory, contains a number of interesting features [1–3]: (i) two kinds of glass transitions, namely a transition of type B (abrupt occurrence of a long-time plateau) at low matrix packing fractions (φ m) and a transition of type A (continuous rise of a long-time plateau) at large φ m (ii) also for large φ m a re-entrancy in the glass transition and (iii) a diffusion-localization transition restricted to the self dynamics (see thin lines in Fig. 1). MCT predicted similar complex features for other systems, which subsequently were found to exist (e.g. [6]).