Latest Research Papers In Condensed Matter Physics | (Cond-Mat.Soft) 2019-01-29
Soft Condensed Matter
Active phase separation in mixtures of chemically-interacting particles (1901.09022v1)
Jaime Agudo-Canalejo, Ramin Golestanian
2019-01-25
Combining theory and simulations, we study mixtures of chemically-interacting particles, which produce or consume a chemical to which they are attracted or repelled, in the most general case of many coexisting species. We find a new class of active phase separation phenomena in which the nonequilibrium chemical interactions between particles, which break action-reaction symmetry, can lead to separation into phases with distinct density and stoichiometry. Our minimal model generically applies to self-organisation of cells and bacteria, catalytic enzymes, or phoretic colloids.
Defects in vertically vibrated monolayers of cylinders (1901.08882v1)
Miguel Gonzalez-Pinto, Johannes Renner, Daniel de las Heras, Yuri Martinez-Raton, Enrique Velasco
2019-01-25
We analyse liquid-crystalline ordering in vertically vibrated monolayers of cylinders confined in a circular cavity. Short cylinders form tetratic arrangements with C
symmetry. This symmetry, which is incompatible with the geometry of the cavity, is restored by the presence of four point defects with total topological charge
. Equilibrium Monte Carlo simulations predict the same structure. A new method to measure the elastic properties of the tetratic medium is developed which exploits the clear similarities between the vibrated dissipative system and the thermal equilibrium system. Our observations open up a new avenue to investigate the formation of defects in response to boundary conditions, an issue which is very difficult to realize in colloidal or molecular systems.
Hydrodynamic interaction between two elastic microswimmers (1901.08854v1)
Mizuki Kuroda, Kento Yasuda, Shigeyuki Komura
2019-01-25
We investigate the hydrodynamic interaction between two elastic swimmers which are composed of three spheres and two harmonic springs. In this model, the natural length of each spring is assumed to undergo a prescribed cyclic change, representing internal states of the swimmer [K. Yasuda et al., J. Phys. Soc. Jpn. 86, 093801 (2017)]. We obtain the average velocities of two identical elastic swimmers as a function of the distance between them both for structurally asymmetric and symmetric swimmers. We show that the mean velocity of the two swimmers is always smaller than that of a single elastic swimmer. The swimming state of two swimmers can be either bound or unbound depending on the relative phase difference between the two elastic swimmers.
Translation-Rotation Coupling in the Dynamics of Linear Molecules in Water (1901.08852v1)
Anjali S Nair, Puja Banerjee, Sarmistha Sarkar, Biman Bagchi
2019-01-25
We study by computer simulations the coupled rotational and translational dynamics of three important linear diatomic molecules, namely, carbon monoxide (CO), nitric oxide (NO) and cyanide ion (CN-) in water. Translational diffusion of these molecules is found to be strongly coupled to their own rotational dynamics which in turn are coupled to similar motions of surrounding water. We examined the validity of hydrodynamic predictions and found them to be largely insufficient, particularly for rotational diffusion. A mode coupling theory approach is developed and applied to understand the complexity of translation-rotation coupling.
The smectic phase in semiflexible polymer materials: A large scale Molecular Dynamics study (1901.08837v1)
Andrey Milchev, Arash Nikoubashman, Kurt Binder
2019-01-25
Semiflexible polymers in concentrated lyotropic solution are studied within a bead-spring model by molecular dynamics simulations, focusing on the emergence of a smectic A phase and its properties. We systematically vary the density of the monomeric units for several contour lengths that are taken smaller than the chain persistence length. The difficulties concerning the equilibration of such systems and the choice of appropriate ensemble (constant volume versus constant pressure, where all three linear dimensions of the simulation box can fluctuate independently) are carefully discussed. Using HOOMD-blue on graphics processing units, systems containing more than a million monomeric units are accessible, making it possible to distinguish the order of the phase transitions that occur. While in this model the nematic-smectic transition is continuous, the transition from the smectic phase to a related crystalline structure with true three-dimensional long-range order is clearly of first order. Further, both orientational and positional correlations of monomeric units are studied as well as the order parameters characterizing the nematic, smectic A, and crystalline phases. The analogy between smectic order and one-dimensional harmonic crystals with respect to the behavior of the structure factor is also explored. Finally, the results are put in perspective with pertinent theoretical predictions and possible experiments.
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