Dissipation by a crystallization process

in Europhysics Letters (2016), 113(10004),

We discuss crystallization as a non-equilibrium process. In a system of hard spheres under compression at a constant rate, we quantify the amount of heat that is dissipated during the crystallization ... [more ▼]

We discuss crystallization as a non-equilibrium process. In a system of hard spheres under compression at a constant rate, we quantify the amount of heat that is dissipated during the crystallization process. We interpret the dissipation as arising from the resistance of the system against phase transformation. An intrinsic compression rate is identified that separates a quasistatic regime from one of rapidly driven crystallization. In the latter regime the system crystallizes more easily, because new relaxation channels are opened, at the cost of forming a higher fraction of non-equilibrium crystal structures. We rationalize the change in the crystallization mechanism by analogy with shear thinning, in terms of a kinetic competition between near-equilibrium relaxation and external driving. [less ▲]

Strong Effect ofWeak Charging in Suspensions of Anisotropic Colloids

in Soft Matter (2014)

Suspensions of hard colloidal particles frequently serve as model systems in studies on fundamental aspects of phase transitions. But often colloidal particles that are considered as ``hard'' are in fact ... [more ▼]

Suspensions of hard colloidal particles frequently serve as model systems in studies on fundamental aspects of phase transitions. But often colloidal particles that are considered as ``hard'' are in fact weakly charged. If the colloids are spherical, weak charging has a only a weak effect on the structural properties of the suspension, which can be easily corrected for. However, this does not hold for anisotropic particles. We introduce a model for the interaction potential between charged ellipsoids of revolution (spheroids) based on the Derjaguin approximation of Debye--Hückel Theory and present a computer simulation study on aspects of the system's structural properties and phase behaviour. In line with previous experimental observations, we find that even a weak surface charge has a strong impact on the correlation functions. A likewise strong impact is seen on the phase behaviour, in particular, we find stable cubatic order in suspensions of oblate ellipsoids. [less ▲]

Mixtures of anisotropic and spherical colloids: Phase behavior, confinement, percolation phenomena and kinetics

in European Physical Journal. Special Topics (2013)

Purely entropic systems such as suspensions of hard rods, platelets and spheres show rich phase behavior. Rods and platelets have successfully been used as models to predict the equilibrium properties of ... [more ▼]

Purely entropic systems such as suspensions of hard rods, platelets and spheres show rich phase behavior. Rods and platelets have successfully been used as models to predict the equilibrium properties of liquid crystals for several decades. Over the past years hard particle models have also been studied in the context of non-equilibrium statistical mechanics, in particular regarding the glass transition, jamming, sedimentation and crystallization. Recently suspensions of hard anisotropic particles also moved into the focus of materials scientists who work on conducting soft matter composites. An insulating polymer resin that is mixed with conductive filler particles becomes conductive when the filler percolates. In this context the mathematical topic of connectivity percolation finds an application in modern nano-technology. In this article, we briefly review recent work on the phase behavior, confinement effects, percolation transition and phase transition kinetics in hard particle models. In the first part, we discuss the effects that particle anisotropy and depletion have on the percolation transition. In the second part, we present results on the kinetics of the liquid-to-crystal transition in suspensions of spheres and of ellipsoids. [less ▲]

Fluctuation Relations and Crystallization in Colloidal Suspensions

Poster (2013, September)

Hard Spheres undergo a fluid to solid phase transition if the packing fraction is above $0.5$. The nucleation process itself and developing structures in this transient process are still matter of current ... [more ▼]

Hard Spheres undergo a fluid to solid phase transition if the packing fraction is above $0.5$. The nucleation process itself and developing structures in this transient process are still matter of current research. \\ Here a new approach is proposed to correlate forming structure and dissipation directly. The system driven externally by a time varying pressure is compressed in a finite time. Thermodynamic work measured and directly correlated to structural information recorded during the process. Fluctuation theorems set the framework of this analysis that still hold at the first order phase transition that are initialized by a macroscopic fluctuation. [less ▲]

Crystallization Close to the Glass Transition: Dynamic heterogeneities do not precede crystallization

Presentation (2013, July)

We address the question whether a crystallization event can be predicted based on observations of the mobility distribution in a supersaturated melt. We have carried out computer simulations of ... [more ▼]

We address the question whether a crystallization event can be predicted based on observations of the mobility distribution in a supersaturated melt. We have carried out computer simulations of overcompressed suspensions of hard monodisperse ellipsoids and observed their crystallization dynamics. The system was compressed very rapidly in order to reach the regime of slow, glass-like dynamics. We nd that, although particle dynamics become sub-diffusive and the intermediate scattering function clearly develops a shoulder, crystallization proceeds via the usual scenario: nucleation and growth for small supersaturations, spinodal decomposition for large supersaturations. In particular, we compared the mobility of the particles in those regions where crystallization set in with the mobility in the rest of the system. We did not find any signature in the dynamics that pointed towards the imminent crystallization event. [less ▲]

Heterogenous Nucleation in Hard Spheres Systems

Scientific Conference (2012, May)

Nucleation in Hard Spheres Systems

Presentation (2012, February 07)

I will be discussing the nucleation process in a system composed of mono-disperse hard spheres initially in an over-compressed fluid state. Molecular dynamics simulations are presented for the homogeneous ... [more ▼]

I will be discussing the nucleation process in a system composed of mono-disperse hard spheres initially in an over-compressed fluid state. Molecular dynamics simulations are presented for the homogeneous system and the dynamics and structure of the forming nucleus including the corresponding nucleation rates are discussed. In comparison to the studied homogenous nucleation event we will extend this system and introduce a substrate to study its influence onto nucleation within the fluid. In this case the substrate is made up of the same type of spheres held fixed in space throughout the simulation process on a triangular lattice modeling a crystalline surface. In general heterogenous nucleation, due to surfaces, walls as well as confinement are of great importancein experiments of colloidal suspensionsbecause strong effects are observed. In our case the substrates influence is studied by varying the substrate lattice constant as well as the fluid density. We observe qualitatively different dynamical regimes that will be discussed in detail. [less ▲]

Description of hard sphere crystals and crystal-fluid interfaces: a critical comparison between density functional approaches and a phase field crystal model

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2012), 86(021404), 1-5

Nucleation in Hard Spheres Systems

Presentation (2011, August)

Entropy production in the nonequilibrium steady states of interacting many-body systems

in Physical Review. E ,Statistical, Nonlinear, and Soft Matter Physics (2011), 83(3),