Particle-Resolved Phase Identification in Two-Dimensional Condensable Systems

Abstract

A method for phase identification (MPI) in two-dimensional (2D) condensable systems is proposed on the basis of the analysis of the Voronoi cells’ characteristics. A simple algorithm is developed for determination of particles belonging to a condensate, a gaseous state, and an interface between them (“surface”). The efficiency and stability of the developed method is studied using molecular dynamics simulations and calculation of binodals in 2D systems with both short- and long-range attraction between particles. To illustrate prospectives of the method for experimental studies, 2D clusters of 2.12 μm diameter colloidal silica particles assembled in a rotating external electric field have been analyzed using the MPI. The results prove that the MPI possesses high accuracy and can be applied to analyze in detail both simulation data (obtained by molecular dynamics or Monte Carlo methods) and results of particle-resolved experimental studies (with colloidal suspensions and complex (dusty) plasmas) of solids and liquids when the considered multiparticle systems can undergo spinodal decomposition. The developed method can be generalized to analyze three-dimensional and multicomponent systems, and therefore, the presented results are of relevance for a broad range of problems in physical chemistry, chemical physics, and materials science.

Phase diagram of two-dimensional colloids with Yukawa repulsion and dipolar attraction

“…Phase states at different magnitudes of rotating magnetic fields and densities can be analyzed using, for example, the method for phase identification. 26 The derived phase diagram can then be directly compared with results of the present paper.…”

“…The liquid-gas binodals were calculated using the plane layer method, which is standard for MD simulations. 26,72,75 After equilibration, the density of the layer (normal to the z-axis) was fitted by the following profile:…”

“…[1][2][3] Two-dimensional (2D) colloidal crystals self-assembled in external fields can act as seeds for 3D structures used in photonics [4][5][6][7][8] as well as for porous media and membranes used for photocatalysis, electrochemical energy storage and conversion, and chemical applications. [9][10][11][12][13] Although tunable interactions can be achieved in different ways (including optical, chemical, and flow-mediated mechanisms 2 ), the use of electric [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] and magnetic 16,[30][31][32][33][34][35][36][37][38][39][40][41] fields is among the most promising due to their technological flexibility, the long-range character of the obtained interactions, and the ability to change them in situ.…”

“…From a fundamental point of view, colloidal suspensions with tunable interactions allow us to perform particle-resolved studies 1,2,[42][43][44][45] to understand basic generic mechanisms of melting and crystallization, condensation and evaporation, spinodal decomposition, slow dynamics in glasses, nucleation, and coalescence, occurring in different regimes of interactions between particles. 1,26,43,[46][47][48] Dipolar attractions induced by external rotating fields have attracted interest in the framework of particle-resolved studies of 2D systems in magnetic 32,35,48 and electric 18,25,26,49 fields. These studies used 2D colloidal suspensions of particles, which were synchronously polarized by an in-plane rotating field, yielding isotropic dipolar attractions ∝1/r 3 at large distances, whose magnitude is determined by the field magnitude and the material properties of the solvent and colloids.…”

Thermodynamics and dynamics of two-dimensional systems with dipolelike repulsive interactions

“…An external electric field polarizes the particles and ion clouds in the solvent around them, inducing a (tunable) dipole-dipole interaction between the particles. Depending on the orientation of the external electric field with respect to the plane of particle confinement, the dipolar interaction potential can be either attractive [24][25][26][27] or repulsive [28][29][30][31][32][33][34].…”