Dynamics and spatial correlation of voids in dense two dimensional colloids

Abstract

Two dimensional (2D) colloids show interesting phase and dynamic behaviors. In 2D, there is another intermediate phase, called hexatic, between isotropic liquid and solid phases. 2D colloids also show strongly correlated dynamic behaviors in hexatic and solid phases. We perform molecular dynamics simulations for 2D colloids and illustrate how the local structure and dynamics of colloids near phase transitions are reflected in the spatial correlations and dynamics of voids. Colloids are modeled as hard discs and a void is defined as a tangent circle (a pore) to three nearest hard discs. The variation in pore diameters represents the degree of disorder in voids and decreases sharply with the area fraction (ϕ) of colloids after a hexagonal structural motif of colloids becomes significant and the freezing transition begins at ϕ ≈ 0.7. The growth of ordered domains of colloids near the phase transition is captured in the spatial correlation functions of pores. We also investigate the topological hopping probability and the topological lifetime of colloids in different topological states, and find that the stability of different topological states should be related to the size variation of local pores: colloids in six-fold states are surrounded by the most ordered and smallest pores with the longest topological lifetime. The topological lifetime of six-fold states increases by about 50 times as ϕ increases from liquid to hexatic to solid phases. We also compare four characteristic times in order to understand the slow and unique dynamics of two dimensional colloids: a caging time (τ(c)), a topological lifetime (τ(top)), a pore lifetime (τ(p)), and a translational relaxation time (τ(α)).

A Journey Through the Landscapes of Small Particles in Binary Colloidal Assemblies: Unveiling Structural Transitions from Isolated Particles to Clusters upon Variation in Composition

“…To give a complementary perspective on the distribution of S particles around L particles, we computed the percentage of L particles “caged” by S particles. The concept of caging in colloidal science has been introduced to study percolation in amorphous assemblies of single-sized colloidal particles [52,60]. Here, we resorted to this concept to individuate those configurations that are likely not to make an L particle “escape” from the set of S nearest neighbors.…”

Incorporation of the intensive and extensive entropy contributions in the disk intersection theory of a hard disk system

“…Instead, in 1980 Speedy proposed the equation of state which relates the pressure with the ratio (average cavity volume)/(average cavity surface area) [11,13]. Since then different geometrical methods of finding the cavities and their surface have become the main emphasis in the ongoing studies of hard particle systems [14][15][16][17][18][19][20][21]. However, the complex shape and connectedness of cavity space makes it very difficult to perform precise measurements of the quantities characterizing them, which resulted in new and new geometrical constructions that are highly nontrivial to implement [14-16, 19, 20].…”

Influences of depletion potential on vapor-liquid critical point metastability

“…Colloid freezing is an important issue, 36 and plays a crucial role in various applications. [37][38][39] Aim of the present work is to improve the AO model and investigate the influences of the two essential control parameters (the solvent fugacity and the size ratio) on the phase behavior of colloid systems and the relevance to controlling and fine-tuning colloid crystallization.…”