Directed self-assembly of spherical caps via confinement

Avendaño, Carlos; Watson, Chekesha M. Liddell; Escobedo, Fernando A.

doi:10.1039/c3sm50833a

Cited by 23 publications

(22 citation statements)

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“…Under strong geometrical confinement, MCS particles exhibit a very rich phase behaviour due to their anisotropic shape and lack of centrosymmetry 58,62 . This behaviour has been confirmed by com-puter simulations of a convex spherical cap model, demonstrating the suitability of the model 56 . Moreover, MCS particles have gained considerable attention due to the possibility of forming photonic band-gap materials with highly anisotropic Brillouin zones.…”

Section: Introductionmentioning

confidence: 52%

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Phase behaviour and gravity-directed self assembly of hard convex spherical caps

McBride

Avendaño

2017

Soft Matter

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We investigate the phase behaviour and self-assembly of convex spherical caps using Monte Carlo simulations. This model is used to represent the main features observed in experimental colloidal particles with mushroom-cap shape [Riley et al., Langmuir, 2010, 26, 1648. The geometry of this non-centrosymmetric convex model is fully characterized by the aspect ratio χ * defined as the spherical cap height to diameter ratio. We use NPT Monte Carlo simulations combined with free energy calculations to determine the most stable crystal structures and the phase behaviour of convex spherical caps with different aspect ratios. We find a variety of crystal structures at each aspect ratio, including plastic and dimer-based crystals; small differences in chemical potential between the structures with similar morphology suggest that convex spherical caps have the tendency to form polycrystalline phases rather than crystallising into a single uniform structure. With the exception of plastic crystals observed at large aspect ratios (χ * > 0.75), crystallisation kinetics seem to be too slow, hindering the spontaneous formation of ordered structures. As an alternative, we also present a study of directing the self-assembly of convex spherical caps via sedimentation onto solid substrates. This study contributes to show how small changes to particle shape can significantly alter the self-assembly of crystal structures, and how a simple gravity field and a template can substantially enhance the process.

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Section: Introductionmentioning

confidence: 52%

“…In this work, we present a computer simulation study of a model of convex spherical caps 56 in bulk and under a gravitational field to direct their self-assembly. The particle model, shown in Figure 1, is used to represent the features of real mushroom cap-shaped (MCS) colloidal particles [57][58][59][60][61] .…”

Section: Introductionmentioning

confidence: 99%

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

McBride

Avendaño

2017

Soft Matter

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“…In fact, they are obtained starting from two different, themselves degenerate, crystals rather than pairing into dimers a previously characterized monomer arrangement. 96,97 Concerning possible ways to continue this work, one could mention three. It would be interesting to conduct a similar study on the rod-like analogues of the disk-like particles considered herein, namely, those hard spindle-shaped particles generated by rotating a circular arc around its subtended chord.…”

Section: Discussionmentioning

confidence: 99%

Hard convex lens-shaped particles: Densest-known packings and phase behavior

Cinacchi

Torquato

2015

The Journal of Chemical Physics

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By using theoretical methods and Monte Carlo simulations, this work investigates dense ordered packings and equilibrium phase behavior (from the low-density isotropic fluid regime to the highdensity crystalline solid regime) of monodisperse systems of hard convex lens-shaped particles as defined by the volume common to two intersecting congruent spheres. We show that, while the overall similarity of their shape to that of hard oblate ellipsoids is reflected in a qualitatively similar phase diagram, differences are more pronounced in the high-density crystal phase up to the densest-known packings determined here. In contrast to those non-(Bravais)-lattice two-particle basis crystals that are the densest-known packings of hard (oblate) ellipsoids, hard convex lens-shaped particles pack more densely in two types of degenerate crystalline structures: (i) non-(Bravais)-lattice two-particle basis body-centered-orthorhombic-like crystals and (ii) (Bravais) lattice monoclinic crystals. By stacking at will, regularly or irregularly, laminae of these two crystals, infinitely degenerate, generally non-periodic in the stacking direction, dense packings can be constructed that are consistent with recent organizing principles. While deferring the assessment of which of these dense ordered structures is thermodynamically stable in the high-density crystalline solid regime, the degeneracy of their densest-known packings strongly suggests that colloidal convex lens-shaped particles could be better glass formers than colloidal spheres because of the additional rotational degrees of freedom. C 2015 AIP Publishing LLC. [http://dx

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“…11 where this feature was ascribed to the development of a cluster isotropic (CI) phase. In the interval P * ∈ [16][17][18] this phase is the only mechanically stable phase. Figure 6 shows a typical image taken at P* = 16.…”

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confidence: 99%

“…16,17 One study, very recent and quite related to the present work, investigates the phase behavior under confinement of hard particles consisting of a sphere cut off by a plane at a certain height. 18 Hard or soft concave particles have been far less studied. To date, the most studied concave particles have an arched shape.…”

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Phase behavior of hard spherical caps

Cinacchi

2013

The Journal of Chemical Physics

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This work reports on the phase behavior of hard spherical caps in the interval of particle shapes delimited by the hard platelet and hemispherical cap models. These very simple model colloidal particles display a remarkably complex phase behavior featuring a competition between isotropicnematic phase separation and clustering as well as a sequence of structures, from roundish to lacy aggregates to no ordinary hexagonal columnar mesophases, all characterized by groups of particles tending to arrange on the same spherical surface. This behavior parallels that one of many molecular systems forming micelles but here it is purely entropy-driven. © 2013 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4822038]The self-assembly of molecular and colloidal systems has always, and nowadays especially, attracted much attention. 1 Recently, in the case of colloids, there has been significant progress in the synthesis of particles of different shape and size as well as in the techniques to visualize the structures they form. 2 These experimental advances offer concrete chances to observe those phase behaviors predicted by theory and numerical simulation; new results from these can in turn stimulate further experimental research. 3 One current example is provided by hard polyhedral particles, to which much numerical and experimental effort is being dedicated. [4][5][6] In theory and simulation, colloidal particles are indeed often assumed to interact through hard-body interactions as these are predominant in directing their packing and shown over the years to be sufficient for the stabilization of a variety of entropy-driven complex fluid phases: nematic (N), 7 smectic, 8 columnar (C), 9 and even cubic gyroid 10 phases can all be obtained in systems of hard-body particles of suitable shape and size.This work considers a special class of hard-body model colloidal particles and examines by numerical simulation their phase behavior featuring both phase separation and aggregation phenomena.The particles are hard spherical caps (HSCs); a preliminary account of their intriguing phase behavior has been given in Ref. 11. Each of these particles is the portion of the surface of a sphere of radius R subtended by an angle θ . The area of this portion is set equal to σ 2 , with σ the unit of length; any particle of this type is thus identified by R* = R/σ (or θ ). By varying R*, hard, generally concave and infinitely thin, particles can be obtained going from the hard platelet, (R* → ∞), through the hard hemispherical cap (R * = 1/ √ 2π ), to the hard sphere (R * = 1/2 √ π) models. It is actually those lens-, bowl-, and vase-like particles that lay in between these limits that are most interesting.HSCs fit current interest for a variety of reasons. These are primarily fundamental but also related to the issues of a) Electronic mail: giorgio.cinacchi@uam.es practical relevance, given, e.g., the wide range of possibilities that nano-sized hollowed particles may offer in catalysis and drug delivery. 12 Several are the viewpoints HSCs can be ...

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Directed self-assembly of spherical caps via confinement

Cited by 23 publications

References 64 publications

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

Hard convex lens-shaped particles: Densest-known packings and phase behavior

Phase behavior of hard spherical caps

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