Towards the self-assembly of anisotropic colloids: Monodisperse oblate ellipsoids

Florea, Daniel; Wyss, Hans M.

doi:10.1016/j.jcis.2013.10.027

Cited by 16 publications

(21 citation statements)

References 44 publications

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“…The value of a is measured from SEM images of dilute samples in which discoids lie flat on the substrate and are far apart from each other. The value of b is obtained from the conservation of volume of the starting sphere 27 , using the relation . These values are also independently verified during the image processing of confocal microscopy images.…”

Section: Methodsmentioning

confidence: 99%

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Metastable orientational order of colloidal discoids

et al. 2015

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The interplay between phase separation and kinetic arrest is important in supramolecular self-assembly, but their effects on emergent orientational order are not well understood when anisotropic building blocks are used. Contrary to the typical progression from disorder to order in isotropic systems, here we report that colloidal oblate discoids initially self-assemble into short, metastable strands with orientational order—regardless of the final structure. The model discoids are suspended in a refractive index and density-matched solvent. Then, we use confocal microscopy experiments and Monte Carlo simulations spanning a broad range of volume fractions and attraction strengths to show that disordered clusters form near coexistence boundaries, whereas oriented strands persist with strong attractions. We rationalize this unusual observation in light of the interaction anisotropy imparted by the discoids. These findings may guide self-assembly for anisotropic systems in which orientational order is desired, such as when tailored mechanical properties are sought.

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Section: Methodsmentioning

confidence: 99%

“…These colloids show unique phase behaviour such as empty liquids 26 , but their size is typically on the order of nanometers—too small for direct imaging. Existing methods used to generate colloidal polymeric discoids in limited quantities include biaxial stretching 27 and blown films 28 .…”

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confidence: 99%

Metastable orientational order of colloidal discoids

et al. 2015

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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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“…New colloidal synthesis methods have stimulated recent work in this area, with a range of anisotropic particles now available, including indented (lock-and-key) particles 8,9 , fused spheres 10,11 , ellipsoids 12 and superballs 4,13 . When such anisotropic particles are mixed with a nonadsorbing polymer, one finds depletion forces between colloids that depend strongly on their orientations [14][15][16] , which can lead to self-assembly of complex structures.…”

Section: Introductionmentioning

confidence: 99%

Coarse-grained depletion potentials for anisotropic colloids: Application to lock-and-key systems

Law

Ashton

Wilding

et al. 2016

The Journal of Chemical Physics

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When colloids are mixed with a depletant such as a non-adsorbing polymer, one observes attractive effective interactions between the colloidal particles. If these particles are anisotropic, analysis of these effective interactions is challenging in general. We present a method for inference of approximate (coarse-grained) effective interaction potentials between such anisotropic particles. Using the example of indented (lock-and-key) colloids, we show how numerical solutions can be used to integrate out the (hard sphere) depletant, leading to a depletion potential that accurately characterises the effective interactions. The accuracy of the method is based on matching of contributions to the second virial coefficient of the colloids. The simplest version of our method yields a piecewise-constant effective potential; we also show how this scheme can be generalised to other functional forms, where appropriate.

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Towards the self-assembly of anisotropic colloids: Monodisperse oblate ellipsoids

Cited by 16 publications

References 44 publications

Metastable orientational order of colloidal discoids

Metastable orientational order of colloidal discoids

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

Coarse-grained depletion potentials for anisotropic colloids: Application to lock-and-key systems

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