Self-diffusion in two-dimensional hard ellipsoid suspensions

Zheng, Zhongyu; Han, Yilong

doi:10.1063/1.3490669

Cited by 59 publications

(59 citation statements)

References 51 publications

(39 reference statements)

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“…In the second place, in-between the solid and the liquid, Kosterlitz, Thouless, Halperin, Nelson, and Young (KTHNY) 17,18 proposed the existence of a hexatic phase. This phase is characterized by quasi-long-range bond orientational correlations, similar to a two-dimensional nematic where orientation is also quasi-long-range ordered 9,[19][20][21][22] , but with a sixfold rather than twofold anisotropy. In their scenario, the solid melts into a hexatic phase, following a dislocation unbinding process, before turning into a liquid by means of disclination unbinding, for decreasing pressure.…”

Section: Introductionmentioning

confidence: 99%

Phase diagram of two-dimensional hard ellipses

Bautista-Carbajal

Odriozola

2014

The Journal of Chemical Physics

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We report the phase diagram of two-dimensional hard ellipses as obtained from replica exchange Monte Carlo simulations. The replica exchange is implemented by expanding the isobaric ensemble in pressure. The phase diagram shows four regions: isotropic, nematic, plastic, and solid (letting aside the hexatic phase at the isotropic-plastic two-step transition [PRL 107, 155704 (2011)]). At low anisotropies, the isotropic fluid turns into a plastic phase which in turn yields a solid for increasing pressure (area fraction). Intermediate anisotropies lead to a single first order transition (isotropic-solid). Finally, large anisotropies yield an isotropic-nematic transition at low pressures and a high-pressure nematic-solid transition. We obtain continuous isotropic-nematic transitions. For the transitions involving quasi-long-range positional ordering, i. e. isotropic-plastic, isotropic-solid, and nematic-solid, we observe bimodal probability density functions. This supports first order transition scenarios.

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Section: Introductionmentioning

confidence: 99%

Phase diagram of two-dimensional hard ellipses

Bautista-Carbajal

Odriozola

2014

The Journal of Chemical Physics

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“…The thermal motion of the ellipsoids was recorded using a charge-coupled device camera resolving 1392×1040 pixels at 1 frame per second (fps) for the highest five concentrations and at 3 fps for lower concentrations. The center-of-mass positions and orientations of individual ellipsoids were tracked using our image processing algorithm [21]. The angular resolution was 1 • and the spatial resolutions were 0.12 µm and 0.04 µm along the long and the short axes respectively.…”

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confidence: 99%

Glass Transitions in Quasi-Two-Dimensional Suspensions of Colloidal Ellipsoids

2011

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We observed a two-step glass transition in monolayers of colloidal ellipsoids by video microscopy. The glass transition in the rotational degree of freedom was at a lower density than that in the translational degree of freedom. Between the two transitions, ellipsoids formed an orientational glass. Approaching the respective glass transitions, the rotational and translational fastest-moving particles in the supercooled liquid moved cooperatively and formed clusters with power-law size distributions. The mean cluster sizes diverge in power law as approaching the glass transitions. The clusters of translational and rotational fastest-moving ellipsoids formed mainly within pseudonematic domains, and around the domain boundaries, respectively. Colloids are outstanding model systems for glass transition studies because the trajectories of individual particles are measurable by video microscopy [1]. In the past two decades, significant experimental effort has been applied to studying colloidal glasses consisting of isotropic particles [1][2][3][4][5], but little to anisotropic particles [6]. The glass transition of anisotropic particles has been studied in three dimensions (3D) mainly through simulation [7,8]. Molecular mode-coupling theory (MMCT) predicts that particle anisotropy should lead to new phenomena in glass transitions [9,10], and some of these have been observed in recent 3D simulations of hard ellipsoids [11,12]. MMCT [10,13] suggests that hard ellipsoids with an aspect ratio p > 2.5 in 3D can form an orientational glass in which rotational degrees of freedom become glass while the center-of-mass motion remains ergodic [9]. Such a "liquid glass" [14], in analogy to a liquid crystal, has not yet been explored in 3D or even 2D experiments. Anisotropic particles should also enable exploration of the dynamic heterogeneity in the rotational degrees of freedom. Moreover the glass transitions of monodispersed particles have not yet been studied in 2D. It is well known that monodispersed spheres can be quenched to a glass in 3D, but hardly in 2D even at the fastest accessible quenching rate. Hence bidispersed or highly polydispersed spheres have been used in experiments [5,15,16], simulations [17] and theory [18] for 2D glasses. In contrast, we found that monodispersed ellipsoids of intermediate aspect ratio are excellent glass formers in 2D because their shape can effectively frustrate crystallization and nematic order.Here we investigate the glass transition in monolayers of colloidal ellipsoids using video microscopy. We measured the translational and rotational relaxation times, the non-Gaussian parameter of the distribution of displacements, and the clusters of cooperative fastestmoving particles. These results consistently showed that the glass transitions of rotational and translational motions occur in two different area fractions, defining an intermediate orientational glass phase.The ellipsoids were synthesized by stretching polymethyl methacrylate (PMMA) spheres [19,20]. They had a small polydispersity...

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“…[31][32][33][34][35][36][37][38][39][40][41] Although the dynamics in monodisperse hard ellipsoidal particles at low and moderate densities has been investigated in recent simulations, 20,42,43 much less information is available concerning the glassy dynamics of hard ellipses [38][39][40][41]44 and hard ellipsoids. 45 The ideal glass transitions in hard ellipsoids of evolution (i.e., hard uniaxial ellipsoids) have theoretically been treated in the framework of molecular mode-coupling theory (MCT).…”

Section: -30mentioning

confidence: 99%

Glass formation in a mixture of hard disks and hard ellipses

Duan

Sun

et al. 2015

The Journal of Chemical Physics

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We present an event-driven molecular dynamics study of glass formation in two-dimensional binary mixtures composed of hard disks and hard ellipses, where both types of particles have the same area. We demonstrate that characteristic glass-formation behavior appears upon compression under appropriate conditions in such systems. In particular, while a rotational glass transition occurs only for the ellipses, both types of particles undergo a kinetic arrest in the translational degrees of freedom at a single density. The translational dynamics for the ellipses is found to be faster than that for the disks within the same system, indicating that shape anisotropy promotes the translational motion of particles. We further examine the influence of mixture's composition and aspect ratio on the glass formation. For the mixtures with an ellipse aspect ratio of k = 2, both translational and rotational glass transition densities decrease with increasing the disk concentration at a similar rate and hence, the two glass transitions remain close to each other at all concentrations investigated. By elevating k, however, the rotational glass transition density diminishes at a faster rate than the translational one, leading to the formation of an orientational glass for the ellipses between the two transitions. Our simulations imply that mixtures of particles with different shapes emerge as a promising model for probing the role of particle shape in determining the properties of glass-forming liquids. Furthermore, our work illustrates the potential of using knowledge concerning the dependence of glass-formation properties on mixture's composition and particle shape to assist in the rational design of amorphous materials.

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Self-diffusion in two-dimensional hard ellipsoid suspensions

Cited by 59 publications

References 51 publications

Phase diagram of two-dimensional hard ellipses

Phase diagram of two-dimensional hard ellipses

Glass Transitions in Quasi-Two-Dimensional Suspensions of Colloidal Ellipsoids

Glass formation in a mixture of hard disks and hard ellipses

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