Colloidal crystals full of invisible vacancies

Frenkel, Daan

doi:10.1073/pnas.1215398109

Cited by 4 publications

(1 citation statement)

References 4 publications

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“…Cubes exhibit a mesophase 27 for a small range of volume fractions (0.51-0.54) which separates isotropic and cubic crystalline phases. 9 There is disagreement in the literature 28,29 about the precise nature of such a mesophase, which hinges on the criterion adopted for classifying a phase as being crystal-like or liquid-crystal-like. For the range of volume fractions specied above, while the average particle positions are crystal-like (despite a high vacancy content), the variance of the position uctuations and particle mobilities are liquid-like.…”

Section: Cubes + Spheres (Cs) Mixturementioning

confidence: 99%

Phase behavior of binary mixtures of hard convex polyhedra

2013

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Shape anisotropy of colloidal nanoparticles has emerged as an important design variable for engineering assemblies with targeted structure and properties. In particular, a number of polyhedral nanoparticles have been shown to exhibit a rich phase behavior [Agarwal et al., Nature Materials, 2011, 10, 230]. Since real synthesized particles have polydispersity not only in size but also in shape, we explore here the phase behavior of binary mixtures of hard convex polyhedra having similar sizes but different shapes. Choosing representative particle shapes from those readily synthesizable, we study in particular four mixtures: (i) cubes and spheres (with spheres providing a non-polyhedral reference case), (ii) cubes and truncated octahedra, (iii) cubes and cuboctahedra, and (iv) cuboctahedra and truncated octahedra. The phase behavior of such mixtures is dependent on the interplay of mixing and packing entropy, which can give rise to miscible or phase-separated states. The extent of mixing of two such particle types is expected to depend on the degree of shape similarity, relative sizes, composition, and compatibility of the crystal structures formed by the pure components. While expectedly the binary systems studied exhibit phase separation at high pressures due to the incompatible pure-component crystal structures, our study shows that the essential qualitative trends in miscibility and phase separation can be correlated to properties of the pure components, such as the relative values of the order-disorder transition pressure (ODP) of each component. Specifically, if for a mixture A+B we have that ODP B

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Section: Cubes + Spheres (Cs) Mixturementioning

confidence: 99%

Phase behavior of binary mixtures of hard convex polyhedra

2013

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Thermodynamics of Melting in Colloids and Helium

Brady

Samulski

2022

J Low Temp Phys

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Enhanced fluctuations pervade a phase near a transition point. This phenomenon was observed in recent simulations of polyhedral particles, where rod-shaped vacancy defects diffused through a solid phase carrying mass flow. The defects proliferated at the melting point, magnifying the mass flow to liquid proportions. Here, we show that the number of vacancies increases on heating or lowering the pressure, in accordance with Boltzmann statistics, but the Boltzmann equilibrium becomes unstable at a threshold number resulting in the first-order melting transition. The instability is driven by an increase in entropy if the defects repel, or by a reduction in enthalpy if they attract. A corresponding thermodynamic instability occurs in other melting transitions, including in argon, colloids, cryogenic helium and simulations of hard spheres. The statistics of the vacancies explains a long-standing anomaly in the heat capacity of solid helium-4, as well as recent measurements of thermally activated mass flow through solid helium-3. In liquid helium-4, the vacancies conform to Feynman’s atomistic and quantum descriptions of rotons and quantitatively account for associated neutron scattering measurements. Colloids, silicon and sodium also melt ‘re-entrantly’ on elevating the pressure, and we identify quantitative evidence that this transition involves the proliferation of interstitial defects.

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Helium II phase: superfluid, supersolid, liquid crystal or spin ice?

Chishko

2022

Molecular Physics

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Colloidal crystals full of invisible vacancies

Cited by 4 publications

References 4 publications

Phase behavior of binary mixtures of hard convex polyhedra

Phase behavior of binary mixtures of hard convex polyhedra

Thermodynamics of Melting in Colloids and Helium

Helium II phase: superfluid, supersolid, liquid crystal or spin ice?

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