Rafal Orlik

Size Selection During Crystallization of Oppositely Charged Nanoparticles

Opposites attract (selectively): Oppositely charged nanoparticles characterized by different size distributions form 3D supracrystals (see figure) only if the distributions overlap. Crystal quality decreases rapidly with decreasing degree of overlap, and, irrespective of the ratio of particle diameters/charges, no crystals are observed for non-overlapping distributions.

The unstable and expanding interface between reacting liquids: theoretical interpretation of negative surface tension

When a chemical reaction between two immiscible liquids creates surfactant molecules at the interface between them, the interfacial surface tension decreases with increasing amount of surfactant. In particular, an interfacial reaction that is faster than the time scale of system’s equilibration can cause a marked increase in the interfacial area due to the surface tension becoming effectively negative. Under these highly nonequilibrium conditions, the interface roughens and develops a variety of interfacial structures ranging from ‘‘ripples’’ to micelle-like formations; in systems of droplets, this process can lead to cycles of droplet elongation and self-division into smaller progenies. In the present work, the emergence and implications of negative surface tension over a ‘‘reactive’’ interface are studied theoretically and using computer simulations. The onset of interfacial instabilities can be described analytically using the methods of linear stability analysis of the continuum theory. For longer times, Molecular Dynamics simulations are implemented which reproduce the formation and increase of interfacial ‘‘ripples’’ at the initial stage, when the interface is a monolayer of surfactant, and widening of the reactive/mixing layer at later times.

Heterogeneous Structure, Heterogeneous Dynamics, and Complex Behavior in Two-Dimensional Liquids.

Analysis of the metrical and topological features of the local structure in a freezing two-dimensional Lennard-Jones system found that in a narrow strip [Formula: see text] of thermodynamic states close to the melting line, the liquid becomes a complex liquid characterized by a super-Arrhenius increase of relaxation times, stretched-exponential decay of correlations in time, and a power-law distribution of waiting times for changes in the local order. In [Formula: see text], the structure of the liquid and its dynamics are spatially heterogeneous; the sizes of ordered clusters are power-law distributed. Those features are governed by local structure evolution between solid-like and liquid-like (disordered) patterns. The liquid inside the strip [Formula: see text] gives a unique opportunity to study how heterogeneous structure, dynamics and complexity are intertwined with each other on a microscopic level.