Preparation of monodisperse ellipsoidal polystyrene particles

Ho, CC; Keller, A.; Odell, J. A.; Ottewill, R. H.

doi:10.1007/bf00657391

Cited by 349 publications

(343 citation statements)

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“…To overcome this obstacle, we carry out real-space experiments, employing direct confocal microscopy [17]. We prepare our colloidal ellipsoids by a uniaxial stretching of PMMA (polymethymethacrylate) spheres [27][28][29][30], 2.4 AE 0.04 μm in diameter, as described elsewhere [4,5]. The particles are fluorescently labeled with Nile red for confocal microscopy and sterically stabilized by a poly-12-hydroxystearic acid (PHSA) monolayer [4,5,11].…”

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confidence: 99%

Structural Transition in a Fluid of Spheroids: A Low-Density Vestige of Jamming

et al. 2016

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A thermodynamically equilibrated fluid of hard spheroids is a simple model of liquid matter. In this model, the coupling between the rotational degrees of freedom of the constituent particles and their translations may be switched off by a continuous deformation of a spheroid of aspect ratio t into a sphere (t ¼ 1). We demonstrate, by experiments, theory, and computer simulations, that dramatic nonanalytic changes in structure and thermodynamics of the fluids take place, as the coupling between rotations and translations is made to vanish. This nonanalyticity, reminiscent of a second-order liquid-liquid phase transition, is not a trivial consequence of the shape of an individual particle. Rather, free volume considerations relate the observed transition to a similar nonanalyticity at t ¼ 1 in structural properties of jammed granular ellipsoids. This observation suggests a deep connection to exist between the physics of jamming and the thermodynamics of simple fluids. DOI: 10.1103/PhysRevLett.116.098001 The thermodynamics of a fluid of simple spheres is wellknown and almost completely understood [1,2]. However, the constituents of real matter are typically nonspherical. Their translational degrees of freedom are coupled to their rotations [3]. A system of spheroids, ellipsoids of revolution, is arguably the simplest model of matter, where such a coupling exists. This model has recently been realized in colloidal and granular matter experiments, providing an important insight onto the local bulk structure of fluids [4,5] and jammed packings [6]. While a very good agreement between experiment and theory has been achieved for the fluids [5,7], these studies dealt with only one specific particle aspect ratio, t ¼ 1.6. The dependence of the fluid structure on the aspect ratio of the constituent particles has not been tested, so that the fundamental role played in these fluids by rotational degrees of freedom remains unknown. The understanding of jammed packings of ellipsoids is incomplete, as well. Many common order metrics are minimized for the, so-called, "maximally random jammed" (MRJ) packings [8]. Yet, it remains unclear, how the various protocols of compression, commonly starting from a fluidlike initial state, explore the available phase space and whether any fundamental physical reason exists for the convergence of many common compression protocols towards packings with densities close to that of the MRJ state [8][9][10][11][12][13].In this work, we study the dependence of the bulk structure in fluids of ellipsoids on the aspect ratio t ¼ a=b of the constituent particles, where a and b are the polar and the equatorial diameters, respectively. We combine experiments, theory, and Monte Carlo (MC) simulations, to explore the fundamental role of the rotational degrees of freedom in these fluids, in the vicinity of the so-called "sphere point" (t ¼ 1), where the coupling between rotations and translations vanishes. We demonstrate that the critical dependence of this coupling on ϵ ≡ jt − 1j, for ϵ → 0, gives rise...

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Structural Transition in a Fluid of Spheroids: A Low-Density Vestige of Jamming

et al. 2016

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“…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 of 5.6% with the semi-long axis a = 3.33 µm and the semi-short axes b = c = 0.56 µm.…”

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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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“…Prolate ellipsoids were obtained by uniaxial stretching of monodisperse polystyrene (PS) spheres (radius R 5 m, Polysciences) essentially following the method of [10]. The aspect ratio, defined as k a=b, was varied from 1 (i.e., a sphere) to 10 (i.e., a rodlike particle).…”

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confidence: 99%