Interdisciplinary complex plasma research: Particle-resolved studies of liquids and solids — A. Ivlev
15 Nov 2012
Alexei Ivlev, Dr. Habil.
Many fundamental issues in classical condensed matter physics, such as crystallization, liquid structure, phase separation, glassy states, etc. can be addressed experimentally by using model systems of individually visible mesoscopic particles (grains) playing the role of “proxy atoms“. The interaction between such “atoms“ is determined by the properties of the surrounding medium and/or by external tuning. Complex plasmas, which represent the plasma state of soft matter, are one of the best known examples of such model systems.
What makes the interdisciplinary complex plasma research so attractive? The answer is quite simple: In complex plasmas, the overall dynamic timescales associated with microparticles (e.g., the inverse Einstein frequency) are in the range of tens of milliseconds, yet the microparticles themselves are large enough to be visualized. Thus, the individual trajectories can be obtained by recording with usual video cameras and, therefore, fully resolved kinetics can be easily reconstructed. Furthermore, the rate of momentum/energy exchange through interactions between the charged microparticles can massively exceed the damping rate due to friction caused by a dilute ambient gas. Therefore, the motion of individual particles in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to “conventional“ liquids and solids in terms of the “atomistic“ dynamics. Two other important aspects are that the form of the pair interaction potential can be tuned externally, and that the complex plasma systems are optically thin (scatter little light), so that thousands of particle layers can be visualized, enabling 3D imaging. Finally, individual particles can be easily manipulated in different ways, so that one can perform active controllable experiments to investigate generic processes occurring in liquids or solids at the most fundamental (individual-particle) level.
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Front of heterogeneous crystallization propagating upwards in complex plasmas. ”Crystalline“ particles appear redder, “fluid“ are multicolored. |
Flow past an obstacle in fluid complex plasmas. (a) Overall topology of the particle flow, the system is approximately symmetric around the vertical axis (exposure time 1 s). The steady vortex flow patterns in the wake are illustrated (1,2). The boundary between the laminar flow and wake becomes unstable – a mixing layer is formed, which grows in width with distance downstream. (b) An example of the mixing layer (an enlargement of the left side, exposure time 0.05 s). The points (lines) represent traces of slow (fast) moving microparticles. |
Because of these properties, interdisciplinary complex plasma research provides us with a unique opportunity to go beyond the limits of continuous media, down to the fundamental length scale of classical systems – the interparticle distance – and thus to investigate all relevant dynamic and structural processes using the fully resolved motion of individual grains, from the onset of cooperative phenomena to large strongly coupled systems (as illustrated in the figures). Hence, the principal aim of such interdisciplinary research is to study generic self-organization processes at the individual-particle level, covering the whole range of non-equilibrium and equilibrium phenomena, at a detail not possible until now.
In this lecture I will discuss recent particle-resolved studies of various generic processes in liquid and solid complex plasmas. I will also briefly summarize and discuss current “hot topics“ and outstanding problems of the interdisciplinary research, where the particle-resolved studies are expected to provide crucial new insights.
The interaction between such “atoms“ is determined by the properties of the surrounding medium and/or by external tuning. Complex plasmas, which represent the plasma state of soft matter, are one of the best known examples of such model systems.What makes the interdisciplinary complex plasma research so attractive? The answer is quite simple: In complex plasmas, the overall dynamic timescales associated with microparticles (e.g., the inverse Einstein frequency) are in the range of tens of milliseconds, yet the microparticles themselves are large enough to be visualized. Thus, the individual trajectories can be obtained by recording with usual video cameras and, therefore, fully resolved kinetics can be easily reconstructed. Furthermore, the rate of momentum/energy exchange through interactions between the charged microparticles can massively exceed the damping rate due to friction caused by a dilute ambient gas. Therefore, the motion of individual particles in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to “conventional“ liquids and solids in terms of the “atomistic“ dynamics. Two other important aspects are that the form of the pair interaction potential can be tuned externally, and that the complex plasma systems are optically thin (scatter little light), so that thousands of particle layers can be visualized, enabling 3D imaging. Finally, individual particles can be easily manipulated in different ways, so that one can perform active controllable experiments to investigate generic processes occurring in liquids or solids at the most fundamental (individual-particle) level./div