Marjolein Dijkstra

Bio: Marjolein Dijkstra is an academic researcher from Utrecht University. The author has contributed to research in topics: Hard spheres & Phase (matter). The author has an hindex of 66, co-authored 343 publications receiving 15087 citations. Previous affiliations of Marjolein Dijkstra include University of Düsseldorf & University of Oxford.

Ionic colloidal crystals of oppositely charged particles.

Abstract: Colloidal suspensions are widely used to study processes such as melting, freezing1,2,3 and glass transitions4,5. This is because they display the same phase behaviour as atoms or molecules, with the nano- to micrometre size of the colloidal particles making it possible to observe them directly in real space3,4. Another attractive feature is that different types of colloidal interactions, such as long-range repulsive1,3, short-range attractive5, hard-sphere-like2,3,4 and dipolar3, can be realized and give rise to equilibrium phases. However, spherically symmetric, long-range attractions (that is, ionic interactions) have so far always resulted in irreversible colloidal aggregation6. Here we show that the electrostatic interaction between oppositely charged particles can be tuned such that large ionic colloidal crystals form readily, with our theory and simulations confirming the stability of these structures. We find that in contrast to atomic systems, the stoichiometry of our colloidal crystals is not dictated by charge neutrality; this allows us to obtain a remarkable diversity of new binary structures. An external electric field melts the crystals, confirming that the constituent particles are indeed oppositely charged. Colloidal model systems can thus be used to study the phase behaviour of ionic species. We also expect that our approach to controlling opposite-charge interactions will facilitate the production of binary crystals of micrometre-sized particles, which could find use as advanced materials for photonic applications7.

Phase diagram of highly asymmetric binary hard-sphere mixtures.

Abstract: We study the phase behavior and structure of highly asymmetric binary hard-sphere mixtures. By first integrating out the degrees of freedom of the small spheres in the partition function we derive a formal expression for the effective Hamiltonian of the large spheres. Then using an explicit pairwise (depletion) potential approximation to this effective Hamiltonian in computer simulations, we determine fluid-solid coexistence for size ratios $q=0.033,0.05,0.1,0.2$, and 1.0. The resulting two-phase region becomes very broad in packing fractions of the large spheres as q becomes very small. We find a stable, isostructural solid-solid transition for $ql~0.05$ and a fluid-fluid transition for $ql~0.10$. However, the latter remains metastable with respect to the fluid-solid transition for all size ratios we investigate. In the limit $\stackrel{\ensuremath{\rightarrow}}{q}0$ the phase diagram mimics that of the sticky-sphere system. As expected, the radial distribution function $g(r)$ and the structure factor $S(k)$ of the effective one-component system show no sharp signature of the onset of the freezing transition and we find that at most points on the fluid-solid boundary the value of $S(k)$ at its first peak is much lower than the value given by the Hansen-Verlet freezing criterion. Direct simulations of the true binary mixture of hard spheres were performed for $qg~0.05$ in order to test the predictions from the effective Hamiltonian. For those packing fractions of the small spheres where direct simulations are possible, we find remarkably good agreement between the phase boundaries calculated from the two approaches---even up to the symmetric limit $q=1$ and for very high packings of the large spheres, where the solid-solid transition occurs. In both limits one might expect that an approximation which neglects higher-body terms should fail, but our results support the notion that the main features of the phase equilibria of asymmetric binary hard-sphere mixtures are accounted for by the effective pairwise depletion potential description. We also compare our results with those of other theoretical treatments and experiments on colloidal hard-sphere mixtures.

Hierarchical self-assembly of suspended branched colloidal nanocrystals into superlattice structures

Abstract: Self-assembly of molecular units into complex and functional superstructures is ubiquitous in biology. The number of superstructures realized by self-assembly of man-made nanoscale units is also growing. However, assemblies of colloidal inorganic nanocrystals 1‐3 are still at an elementary level, not only because of the simplicity of the shape of the nanocrystal building blocks and their interactions, but also because of the poor control over these parameters in the fabrication of more elaborate nanocrystals. Here, we show how monodisperse colloidal octapod-shaped nanocrystals self-assemble, in a suitable solution environment, on two sequential levels. First, linear chains of interlocked octapods are formed, and subsequently the chains spontaneously self-assemble into threedimensional superstructures. Remarkably, all the instructions for the hierarchical self-assembly are encoded in the octapod shape. The mechanical strength of these superstructures is improvedbyweldingtheconstituentnanocrystalstogether. The organization of colloidal nanocrystals into ordered structures is a necessary step towards the fabrication of artificial solids and new devices. Superstructures can be built either by self-assembly directly in solution, or on a substrate following solvent evaporation or de-wetting 4 6 . A variety of forces can be involved in their formation: van der Waals (vdW) attractions between the particles, steric repulsions between the hydrophobic tails of the surfactants (often coating the nanocrystal surface), capillary forces during solvent evaporation, attractive depletion forces, Coulomb forces between surface charges or electric dipoles, and magnetic forces 1,3,5,7 12 . The assembly of many ordered threedimensional (3D) superstructures, for example, simple, binary, or ternary assemblies of spherical nanoparticles 13 17 , and smectic-like multilayers of hexagonally packed nanorods 18 , as well as liquid crystalline phases, is found to be solely driven by entropy 19 21 . More elaborate assemblies could be achieved from such simple building blocks by encoding information for the self-assembly in the surface pattern of the nanoparticles, for instance by DNA functionalization to modify the strength and directionality of particleparticle

Self-assembly route for photonic crystals with a bandgap in the visible region.

Abstract: Three-dimensional photonic crystals, or periodic materials, that do not allow the propagation of photons in all directions with a wavelength in the visible region have not been experimentally fabricated, despite there being several potential structures and the interesting applications and physics that this would lead to1. We show using computer simulations that two structures that would enable a bandgap in the visible region, diamond and pyrochlore, can be self-assembled in one crystal structure from a binary colloidal dispersion. In our approach, these two structures are obtained as the large (Mg) and small (Cu) sphere components of the colloidal analogue of the MgCu2 Laves phase2, whose growth can be selected and directed using appropriate wall patterning. The method requires that the particles consist of different materials, so that one of them can be removed selectively after drying (for example, by burning or dissolution). Photonic calculations show that gaps appear at relatively low frequencies indicating that they are robust and open for modest contrast, enabling fabrication from more materials.

Surface roughness directed self-assembly of patchy particles into colloidal micelles.

Abstract: Colloidal particles with site-specific directional interactions, so called “patchy particles”, are promising candidates for bottom-up assembly routes towards complex structures with rationally designed properties. Here we present an experimental realization of patchy colloidal particles based on material independent depletion interaction and surface roughness. Curved, smooth patches on rough colloids are shown to be exclusively attractive due to their different overlap volumes. We discuss in detail the case of colloids with one patch that serves as a model for molecular surfactants both with respect to their geometry and their interactions. These one-patch particles assemble into clusters that resemble surfactant micelles with the smooth and attractive sides of the colloids located at the interior. We term these clusters “colloidal micelles”. Direct Monte Carlo simulations starting from a homogeneous state give rise to cluster size distributions that are in good agreement with those found in experiments. Important differences with surfactant micelles originate from the colloidal character of our model system and are investigated by simulations and addressed theoretically. Our new “patchy” model system opens up the possibility for self-assembly studies into finite-sized superstructures as well as crystals with as of yet inaccessible structures.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Anisotropy of building blocks and their assembly into complex structures

Abstract: A revolution in novel nanoparticles and colloidal building blocks has been enabled by recent breakthroughs in particle synthesis These new particles are poised to become the ‘atoms’ and ‘molecules’ of tomorrow’s materials if they can be successfully assembled into useful structures Here, we discuss the recent progress made in the synthesis of nanocrystals and colloidal particles and draw analogies between these new particulate building blocks and better-studied molecules and supramolecular objects We argue for a conceptual framework for these new building blocks based on anisotropy attributes and discuss the prognosis for future progress in exploiting anisotropy for materials design and assembly