1,721,021 research outputs found
Patterning symmetry in the rational design of colloidal crystals
Full text linkColloidal particles have the right size to form ordered structures with periodicities comparable to the wavelength of visible light. The tantalizing colours of precious opals and the colour of some species of birds are examples of polycrystalline colloidal structures found in nature. Driven by the demands of several emergent technologies, efforts have been made to develop efficient, self-assembly-based methodologies for generating colloidal single crystals with well-defined morphologies. Somewhat unfortunately, these efforts are often frustrated by the formation of structures lacking long-range order. Here we show that the rational design of patch shape and symmetry can drive patchy colloids to crystallize in a single, selected morphology by structurally eliminating undesired polymorphs. We provide a proof of this concept through the numerical investigation of triblock Janus colloids. One particular choice of patch symmetry yields, via spontaneous crystallization, a pure tetrastack lattice, a structure with attractive photonic properties, whereas another one results in a colloidal clathrate-like structure, in both cases without any interfering polymorphs
Switching bonds in a DNA gel: An all-DNA vitrimer
No full textWe design an all-DNA system that behaves like vitrimers, innovative plastics with self-healing and stress-releasing properties. The DNA sequences are engineered to self-assemble first into tetra- and bifunctional units which, upon further cooling, bind to each other forming a fully bonded network gel. An innovative design of the binding regions of the DNA sequences, exploiting a double toehold-mediated strand displacement, generates a network gel which is able to reshuffle its bonds, retaining at all times full bonding. As in vitrimers, the rate of bond switching can be controlled via a thermally activated catalyst, which in the present design is very short DNA strands
Gas-liquid phase coexistence in a tetrahedral patchy particle model
No full textWe evaluate the location of the gas–liquid coexistence line and of the associated critical point for the primitive model for water (PMW), introduced by Kolafa and Nezbeda (1987 Mol. Phys. 61 161). Besides being a simple model for a molecular network forming liquid, the PMW is representative of patchy proteins and novel colloidal particles interacting with localized directional short-range attractions. We show that the gas–liquid phase separation is metastable, i.e. it takes place in the region of the phase diagram where the crystal phase is thermodynamically favoured, as in the case of particles interacting via short-range attractive spherical potentials. We do not observe crystallization close to the critical point. The region of gas–liquid instability of this patchy model is significantly reduced as compared to that from equivalent models of spherically interacting particles, confirming the possibility of observing kinetic arrest in a homogeneous sample driven by bonding as opposed to packing
Novel stable crystalline phase for the Stillinger-Weber potential
Full text linkTetrahedral liquids such as silicon, germanium, carbon, water, and silica are an important class of materials not only for industrial applications but also for our understanding of nature. The Stillinger-Weber potential is one of the most popular models for computer simulations of these systems with tetrahedral coordination, with the directionality of the interactions introduced via a three-body repulsive term which promotes locally tetrahedral arrangements. This approach has been extended to various tetrahedral liquids, providing valuable insight into the physics of group XIV elements and more recently water. Perhaps surprisingly, a consistent thermodynamic picture of this class of models is still lacking despite their widespread usage. Here we fill this gap by computing equilibrium phase diagrams for the silicon and water parametrizations and report a novel crystal structure which dominates the models' phase diagram at intermediate and high pressure, and thus warrants further theoretical and numerical investigation. Our results redefine the phase behavior of an important class of tetrahedrally coordinated systems, and also suggest that a more stringent test for simulation models is the ability to select the experimentally relevant crystalline phases, as opposed to just reproducing their mechanical stability
COLLOIDAL SELF-ASSEMBLY Patchy from the bottom up
No full textThe realization of a self-assembled kagome lattice from colloids with attractive hydrophobic patches offers a simple but powerful example of the bottom-up design strategy
A Nucleotide-Level Computational Approach to DNA-Based Materials
No full textPerhaps the most important feature for the biological role of DNA is its outstanding molecular recognition capability. Beyond its biological importance, this intrinsic selectivity can be exploited for artificial applications, which range from nanotechnology to materials science. Here we provide a short introduction on DNA and on the features that make it attractive as a building block for new materials. Then, we present an overview of the state of the art of DNA modelling, with a strong focus on nucleotide-level coarse-grained models which, thanks to their vast range of applicability, are ideal candidates for the investigation of the phase behaviour of all-DNA materials. Finally, we show how a specific model, oxDNA, has been used to asses the thermodynamics and structural properties of two recently-synthesised DNA-based materials: gels made of DNA nanostars and liquid crystals made of ultra-short DNA duplexes
Two dimensional assembly of triblock Janus particles into crystal phases in the two bond per patch limit
Full text linkIn recent experimental work on spherical colloidal particles decorated with two hydrophobic poles separated by an electrically charged middle band (triblock Janus particles)-when particles are confined by gravity at the bottom of the sample holder-self-assembly into a Kagome two dimensional lattice has been documented [Qian Chen, Sung Chul Bae and Steve Granick, Nature, 2011, 469, 381]. Here, we assess the ability of a simple two-patch effective potential to reproduce the experimental findings. The model parameters are selected to match the experimental values, with a short-range attraction mimicking hydrophobic interactions and a patch width that allows for a maximum of two contacts per patch. We show that the effective potential is able to reproduce the observed crystallisation pathway in the Kagome structure. On the basis of free energy calculations, we also show that the Kagome lattice is stable at low temperature and low pressure, but that it transforms into a hexagonal lattice with alternating attractive and repulsive bands on increasing pressure
Designing Patchy Interactions to Self-Assemble Arbitrary Structures
No full textOne of the fundamental goals of nanotechnology is to exploit selective and directional interactions between molecules to design particles that self-assemble into desired structures, from capsids, to nanoclusters, to fully formed crystals with target properties (e.g., optical, mechanical, etc.). Here, we provide a general framework which transforms the inverse problem of self-assembly of colloidal crystals into a Boolean satisfiability problem for which solutions can be found numerically. Given a reference structure and the desired number of components, our approach produces designs for which the target structure is an energy minimum, and also allows us to exclude solutions that correspond to competing structures. We demonstrate the effectiveness of our approach by designing model particles that spontaneously nucleate milestone structures such as the cubic diamond, the pyrochlore, and the clathrate lattices
Gels of DNA nanostars never crystallize
No full textUsing state-of-the-art numerical techniques, we show that, upon lowering the temperature, tetravalent DNA nanostars form a thermodynamically stable, fully bonded equilibrium gel. In contrast to atomic and molecular network formers, in which the disordered liquid is always metastable with respect to some crystalline phase, we find that the DNA nanostar gel has a lower free energy than the diamond crystal structure in a wide range of concentrations. This unconventional behavior, here verified for the first time in a realistic model, arises from the large arm flexibility of the DNA nanostars, a property that can be tuned by design. Our results confirm the thermodynamic stability of the recently experimentally realized DNA hydrogels
Role of the Range in the Fluid-Crystal Coexistence for a Patchy Particle Model
No full textWe evaluate the phase diagram of the four-site Kern−Frenkel patchy particle model [Kern, N.; Frenkel, D. J. Chem. Phys. 2003, 118, 9882.], a model representative of particles interacting via short-range orientational interactions, for several values of the interaction range. Similar to what has been found for isotropic potentials, the liquid phase disappears as an equilibrium phase for values of the range on the order of 15% of the particle diameter. For smaller ranges, the gas−liquid phase separation becomes metastable with respect to crystallization into a diamond-like structure. Interestingly, and differently from the isotropic case, the supersaturation of the fluid at the critical point does not significantly increase upon going toward the adhesive (vanishing interaction range) limit
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