We report theoretical and numerical evaluations of the phase diagram for patchy colloidal particles of new generation. We show that the reduction of the number of bonded nearest neighbours offers the possibility of generating liquid states (i.e. states with temperature T lower than the liquidgas critical temperature) with a vanishing occupied packing fraction (φ), a case which can not be realized with spherically interacting particles. Theoretical results suggest that such reduction is accompanied by an increase of the region of stability of the liquid phase in the (T -φ) plane, possibly favoring the establishment of homogeneous disordered materials at small φ, i.e. stable equilibrium gels.The physico-chemical manipulation of colloidal particles is growing at an incredible pace. The large freedom in the control of the inter-particle potential has made it possible to design colloidal particles which significantly extend the possibilities offered by atomic systems [1]. An impressive step further is offered by the newly developed techniques to assemble (and produce with significant yield) colloidal molecules, particles decorated on their surface by a predefined number of attractive sticky spots, i.e. particles with specifically designed shapes and interaction sites [2,3,4,5]. These new particles, thanks to the specificity of the built-in interactions, will be able not only to reproduce molecular systems on the nano and micro scale, but will also show novel collective behaviors. To guide future applications of patchy colloids, to help designing bottom-up strategies in self-assembly [6,7,8] and to tackle the issue of interplay between dynamic arrest and crystallisation -a hot-topic related for example to the possibility of nucleating a colloidal diamond crystal structure for photonic applications [9] -it is crucial to be able to predict the region in the (T -φ) plane in which clustering, phase separation or even gelation is expected.While design and production of patchy colloids is present-day research, unexpectedly theoretical studies of the physical properties of these systems have a longer history, starting in the eighties in the context of the physics of associated liquids [10,11,12,13,14,15]. These studies, in the attempt to pin-down the essential features of association, modelled molecules as hard-core particles with attractive spots on the surface, a realistic description of the recently created patchy colloidal particles. A thermodynamic perturbation theory (TPT) appropriate for these models was introduced by Wertheim [16] to describe association under the hypothesis that a sticky site on a particle cannot bind simultaneously to two (or more) sites on another particle. Such a condition can be naturally implemented in colloids, due to the relative size of the particle as compared to the range of the sticky interaction. These old studies provide a very valuable starting point for addressing the issue of the phase diagram of this new class of colloids, and in particular of the role of the patches number.In this ...

We study a model in which particles interact with short-ranged attractive and long-ranged repulsive interactions, in an attempt to model the equilibrium cluster phase recently discovered in sterically stabilized colloidal systems in the presence of depletion interactions. At low packing fractions, particles form stable equilibrium clusters which act as building blocks of a cluster fluid. We study the possibility that cluster fluids generate a low-density disordered arrested phase, a gel, via a glass transition driven by the repulsive interaction. In this model the gel formation is formally described with the same physics of the glass formation.

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 A 3 ͑cusp͒ singularity. On increasing the square-well width, the glass-glass line disappears, giving rise to a fourthorder A 4 ͑swallow-tail͒ singularity at a critical well width. Close to the A 3 and A 4 singularities the decay of the density correlators shows stretching of huge dynamical windows, in particular logarithmic time dependence.

We present a quantitative description of the thermodynamics in a supercooled binary Lennard Jones liquid via the evaluation of the degeneracy of the inherent structures, i.e. of the number of potential energy basins in configuration space. We find that for supercooled states, the contribution of the inherent structures to the free energy of the liquid almost completely decouples from the vibrational contribution. An important byproduct of the presented analysis is the determination of the Kauzmann temperature for the studied system. The resulting quantitative picture of the thermodynamics of the inherent structures offers new suggestions for the description of equilibrium and out-of-equilibrium slow-dynamics in liquids below the Mode-Coupling temperature.

We present a molecular-dynamics study of the self-dynamics of water molecules in deeply supercooled liquid states. We find that the decay of single-particle dynamics correlation functions is characterized by a fast initial relaxation toward a plateau and by a region of self-similar dynamics, followed at late times by a stretched exponential decay. We interpret such results in the framework of the mode-coupling theory for supercooled liquids. We relate the apparent anomalies of the transport coefficients in water on lowering the temperature to the formation of cages and to the associated slow dynamics resulting from the presence of long-lived molecular cages. The so-called critical Angell temperature in supercooled water could thus be interpreted as kinetic glass transition temperature, relaxing the need of a thermodynamic singularity for the explanation of the anomalies of Liquid water

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This review focuses on recent developments in the theoretical, numerical and experimental study of slow dynamics in colloidal systems, with a particular emphasis on the glass transition phenomenon. Colloidal systems appear to be particularly suited for tackling the general problem of dynamic arrest, since they show a larger flexibility compared to atomic and molecular glasses because of their size and the possibility of manipulating the physical and chemical properties of the samples. Indeed, a wealth of new effects, not easily observable in molecular liquids, have been predicted and measured in colloidal systems. The slow dynamic behavior of three classes of colloidal suspension is reviewed - hard colloids, short-range attractive colloids and soft colloidal systems - selecting the model systems among the most prominent candidates for grasping the essential features of dynamic arrest. Emphasis is on the possibility of performing a detailed comparison between experimental data and theoretical predictions based on the mode coupling theory of the glass transition. Finally, the importance of understanding the system's kinetic arrest phase diagram, i.e. the regions in phase space where disordered arrested states can be expected, is stressed. When and how these states are kinetically stabilized with respect to the ordered lowest free energy phases is then examined in order to provide a framework for interpreting and developing new ideas in the study of new materials

We report extensive numerical simulations of a simple model for charged colloidal particles in suspension with small nonadsorbing polymers. The chosen effective one-component interaction potential is composed of a short-range attractive part complemented by a Yukawa repulsive tail. We focus on the case where the screening length is comparable to the particle radius. Under these conditions, at low temperature, particles locally cluster into quasi one-dimensional aggregates which, via a branching mechanism, form a macroscopic percolating gel structure. We discuss gel formation and contrast it with the case of longer screening lengths, for which previous studies have shown that arrest is driven by the approach to a Yukawa glass of spherical clusters. We compare our results with recent experimental work on charged colloidal suspensions (Phys. Rev. Lett. 2005, 94, 208301).