20 research outputs found
Predicting the self-assembly of a model colloidal crystal
We investigate the self-assembly (crystallisation) of particles with hard
cores and isotropic, square-well interactions, using a Monte Carlo scheme to
simulate overdamped Langevin dynamics. We measure correlation and response
functions during the early stages of assembly, and we analyse the results using
fluctuation-dissipation theorems, aiming to predict which systems will
self-assemble successfully and which will get stuck in disordered states. The
early-time correlation and response measurements are made before significant
crystallisation has taken place, indicating that dynamical measurements are
valuable in measuring a system's propensity for kinetic trapping
Complexity in surfaces of densest packings for families of polyhedra
Packings of hard polyhedra have been studied for centuries due to their
mathematical aesthetic and more recently for their applications in fields such
as nanoscience, granular and colloidal matter, and biology. In all these
fields, particle shape is important for structure and properties, especially
upon crowding. Here, we explore packing as a function of shape. By combining
simulations and analytic calculations, we study three 2-parameter families of
hard polyhedra and report an extensive and systematic analysis of the densest
packings of more than 55,000 convex shapes. The three families have the
symmetries of triangle groups (icosahedral, octahedral, tetrahedral) and
interpolate between various symmetric solids (Platonic, Archimedean, Catalan).
We find that optimal (maximum) packing density surfaces that reveal unexpected
richness and complexity, containing as many as 130 different structures within
a single family. Our results demonstrate the utility of thinking of shape not
as a static property of an object in the context of packings, but rather as but
one point in a higher dimensional shape space whose neighbors in that space may
have identical or markedly different packings. Finally, we present and
interpret our packing results in a consistent and generally applicable way by
proposing a method to distinguish regions of packings and classify types of
transitions between them.Comment: 16 pages, 8 figure
Controlling crystal self-assembly using a real-time feedback scheme
We simulate crystallisation of hard spheres with short-ranged attractive potentials as a model self-assembling system. Using measurements of correlation and response functions, we develop a method whereby the interaction parameters between the particles are automatically tuned during the assembly process, in order to obtain high-quality crystals and avoid kinetic traps. The method we use is independent of the details of the interaction potential and of the structure of the final crystal - we propose that it can be applied to a wide range of self-assembling systems
Digital Alchemy for Materials Design: Colloids and Beyond
Starting with the early alchemists, a holy grail of science has been to make
desired materials by modifying the attributes of basic building blocks.
Building blocks that show promise for assembling new complex materials can be
synthesized at the nanoscale with attributes that would astonish the ancient
alchemists in their versatility. However, this versatility means that making
direct connection between building block attributes and bulk behavior is both
necessary for rationally engineering materials, and difficult because building
block attributes can be altered in many ways. Here we show how to exploit the
malleability of the valence of colloidal nanoparticle "elements" to directly
and quantitatively link building block attributes to bulk behavior through a
statistical thermodynamic framework we term "digital alchemy". We use this
framework to optimize building blocks for a given target structure, and to
determine which building block attributes are most important to control for
self assembly, through a set of novel thermodynamic response functions, moduli
and susceptibilities. We thereby establish direct links between the attributes
of colloidal building blocks and the bulk structures they form. Moreover, our
results give concrete solutions to the more general conceptual challenge of
optimizing emergent behaviors in nature, and can be applied to other types of
matter. As examples, we apply digital alchemy to systems of truncated
tetrahedra, rhombic dodecahedra, and isotropically interacting spheres that
self assemble diamond, FCC, and icosahedral quasicrystal structures,
respectively.Comment: 17 REVTeX pages, title fixed to match journal versio
Clusters of polyhedra in spherical confinement
What is the best way to pack objects into a container? This simple question, one that is relevant to everyday life, biology, and nanoscience, is easy to state but surprisingly difficult to answer. Here, we use computational methods to determine dense packings of a set of polyhedra inside a sphere, for up to 60 constituent packers. Our dense packings display a wide variety of symmetries and structures, and indicate that the presence of the spherical container suppresses packing effects due to polyhedral shape. Our results have implications for a range of biological phenomena and experimental applications, including blood clotting, cell aggregation, drug delivery, colloidal engineering, and the creation of metamaterials