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Wrocław, Poland

Pawlik G.,Wroclaw University of Technology | Orlik R.,Orlik Software | Radosz W.,Wroclaw University of Technology | Mitus A.C.,Wroclaw University of Technology | Kuzyk M.G.,Washington State University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Recently we have formulated a simple Monte Carlo model1 for the study of the photomechanical effect in polymeric fibers pumped with a linearly polarized laser beam.2-4 The model fiber is a host - guest system consisting of the polymeric matrix and azodye chromophores, which undergo multiple trans - cis - trans cycles when illuminated by linearly polarized light. Current paper is focused on the topic so-far neglected in,1 closely related to the hypothetical cooperative mechanism of stress relaxation2-4 - on the characterization of local voids in computer-generated polymeric matrix. We study void-size distributions and void-void correlation functions. © 2012 SPIE.

Patashinski A.Z.,Northwestern University | Ratner M.A.,Northwestern University | Grzybowski B.A.,Northwestern University | Orlik R.,Orlik Software | Mitus A.C.,Wroclaw University of Technology
Journal of Physical Chemistry Letters | Year: 2012

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 L 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 L, 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 L gives a unique opportunity to study how heterogeneous structure, dynamics and complexity are intertwined with each other on a microscopic level. © 2012 American Chemical Society.

Patashinski A.,Northwestern University | Orlik R.,Orlik Software | Ratner M.,Northwestern University | Grzybowski B.A.,Northwestern University
Soft Matter | Year: 2010

To investigate the nature of mixing in reacting liquids, a two-dimensional system comprising two partly miscible liquids A and B that can form surface-active AB dimers was studied using Molecular Dynamics simulations. In the initial state, A and B occupied different parts of the system and were separated by a planar interface. Due to the A + B ↔ AB reaction, this interface became unstable and the liquids mixed. When the reaction was fast, it facilitated pronounced flows on molecular as well as larger scales. These non-equilibrium motions broke-up large, homogeneous regions into progressively smaller clusters surrounded by the AB dimers. This process substantially enhanced the mixing of A and B. The reaction created a variety of markedly different final morphologies depending on the reaction rate, component miscibility, and other parameters. © 2011 The Royal Society of Chemistry.

Patashinski A.Z.,Northwestern University | Orlik R.,Orlik Software | Mitus A.C.,Wroclaw University of Technology | Grzybowski B.A.,Northwestern University | Ratner M.A.,Northwestern University
Journal of Physical Chemistry C | Year: 2010

A typical configuration of an equilibrium 2D system of 2500 Lennard-Jones particles at melting is found to be a mosaic of crystallites and amorphous clusters. This mosaic significantly changed at times around the period τ of local vibrations, while most particles retain their nearest neighbors for times much longer than τ. In a system of 2500 particles, we found no phase separation for length scales larger than that of a crystallite. With decreasing density, the number of small amorphous clusters increased, and proliferation and percolation of amorphous matter separated the crystalline-ordered parts so that correlations between local order orientations of remote crystallites disappeared. We suggest that the mosaic is a manifestation of diminished stability of the crystalline structure resulting from competition between attraction and repulsion forces. © 2010 American Chemical Society.

Patashinski A.Z.,Northwestern University | Orlik R.,Orlik Software | Paclawski K.,AGH University of Science and Technology | Ratner M.A.,Northwestern University | Grzybowski B.A.,Northwestern University
Soft Matter | Year: 2012

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. © 2012 The Royal Society of Chemistry.

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