59 research outputs found
Tailoring the Phonon Band Structure in Binary Colloidal Mixtures
We analyze the phonon spectra of periodic structures formed by
two-dimensional mixtures of dipolar colloidal particles. These mixtures display
an enormous variety of complex ordered configurations [J. Fornleitner {\it et
al.}, Soft Matter {\bf 4}, 480 (2008)], allowing for the systematic
investigation of the ensuing phonon spectra and the control of phononic gaps.
We show how the shape of the phonon bands and the number and width of the
phonon gaps can be controlled by changing the susceptibility ratio, the
concentration and the mass ratio between the two components.Comment: 4 pages 3 figure
Procedure to construct a multi-scale coarse-grained model of DNA-coated colloids from experimental data
We present a quantitative, multi-scale coarse-grained model of DNA coated
colloids. The parameters of this model are transferable and are solely based on
experimental data. As a test case, we focus on nano-sized colloids carrying
single-stranded DNA strands of length comparable to the colloids' size. We show
that in this regime, the common theoretical approach of assuming pairwise
additivity of the colloidal pair interactions leads to quantitatively and
sometimes even qualitatively wrong predictions of the phase behaviour of
DNA-grafted colloids. Comparing to experimental data, we find that our
coarse-grained model correctly predicts the equilibrium structure and melting
temperature of the formed solids. Due to limited experimental information on
the persistence length of single-stranded DNA, some quantitative discrepancies
are found in the prediction of spatial quantities. With the availability of
better experimental data, the present approach provides a path for the rational
design of DNA-functionalised building blocks that can self-assemble in complex,
three-dimensional structures.Comment: 17 pages, 10 figures; to be published in Soft Matte
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Blood Flow in silico: From Single Cells to Blood Rheology
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Mesoscale hydrodynamics simulations of red blood cells under flow have provided much new
insight into their shapes and dynamics in microchannel flow. The presented results range from the behavior
of single cells in confinement and the shape changes in sedimentation, to the clustering and arrangement of
many cells in microchannels and the viscosity of red blood cell suspensions under shear flow. The interaction
of red blood cells with other particles and cells, such as white blood cells, platelets, and drug carriers, shows
an essential role of red blood cells in the margination of other blood components
Novel Ground-State Crystals with Controlled Vacancy Concentrations: From Kagom\'{e} to Honeycomb to Stripes
We introduce a one-parameter family, , of pair potential
functions with a single relative energy minimum that stabilize a range of
vacancy-riddled crystals as ground states. The "quintic potential" is a
short-ranged, nonnegative pair potential with a single local minimum of height
at unit distance and vanishes cubically at a distance of \rt. We have
developed this potential to produce ground states with the symmetry of the
triangular lattice while favoring the presence of vacancies. After an
exhaustive search using various optimization and simulation methods, we believe
that we have determined the ground states for all pressures, densities, and . For specific areas below 3\rt/2, the ground states of the
"quintic potential" include high-density and low-density triangular lattices,
kagom\'{e} and honeycomb crystals, and stripes. We find that these ground
states are mechanically stable but are difficult to self-assemble in computer
simulations without defects. For specific areas above 3\rt/2, these systems
have a ground-state phase diagram that corresponds to hard disks with radius
\rt. For the special case of H=0, a broad range of ground states is
available. Analysis of this case suggests that among many ground states, a
high-density triangular lattice, low-density triangular lattice, and striped
phases have the highest entropy for certain densities. The simplicity of this
potential makes it an attractive candidate for experimental realization with
application to the development of novel colloidal crystals or photonic
materials.Comment: 25 pages, 11 figure
Quantitative prediction of the phase diagram of DNA-functionalized nano-colloids
We present a coarse-grained model of DNA-functionalized colloids that is
computationally tractable. Importantly, the model parameters are solely based
on experimental data. Using this highly simplified model, we can predict the
phase behavior of DNA-functionalized nano-colloids without assuming pairwise
additivity of the inter-colloidal interactions. Our simulations show that for
nano-colloids, the assumption of pairwise additivity leads to substantial
errors in the estimate of the free energy of the crystal phase. We compare our
results with available experimental data and find that the simulations predict
the correct structure of the solid phase and yield a very good estimate of the
melting temperature. Current experimental estimates for the contour length and
persistence length of single-stranded DNA sequences are subject to relatively
large uncertainties. Using the best available estimates, we obtain predictions
for the crystal lattice constants that are off by a few percent: this indicates
that more accurate experimental data on ssDNA are needed to exploit the full
power of our coarse-grained approach.Comment: 4 pages, 2 figures; accepted for publication in Phys. Rev. Let
Lane-formation vs. cluster-formation in two dimensional square-shoulder systems: A genetic algorithm approach
Introducing genetic algorithms as a reliable and efficient tool to find
ordered equilibrium structures, we predict minimum energy configurations of the
square shoulder system for different values of corona width . Varying
systematically the pressure for different values of we obtain
complete sequences of minimum energy configurations which provide a deeper
understanding of the system's strategies to arrange particles in an
energetically optimized fashion, leading to the competing self-assembly
scenarios of cluster-formation vs. lane-formation.Comment: 5 pages, 6 figure
Self-assembly of binary nanoparticle dispersions: from square arrays and stripe phases to colloidal corrals
The generation of nanoscale square and stripe patterns is of major
technological importance since they are compatible with industry-standard
electronic circuitry. Recently, a blend of diblock copolymer interacting via
hydrogen-bonding was shown to self-assemble in square arrays. Motivated by
those experiments we study, using Monte Carlo simulations, the pattern
formation in a two-dimensional binary mixture of colloidal particles
interacting via isotropic core-corona potentials. We find a rich variety of
patterns that can be grouped mainly in aggregates that self-assemble in regular
square lattices or in alternate strips. Other morphologies observed include
colloidal corrals that are potentially useful as surface templating agents.
This work shows the unexpected versatility of this simple model to produce a
variety of patterns with high technological potential.Comment: 13 pages, 5 figures, submitte
The zero-temperature phase diagram of soft-repulsive particle fluids
Effective pair interactions with a soft-repulsive component are a well-known
feature of polymer solutions and colloidal suspensions, but they also provide a
key to interpret the high-pressure behaviour of simple elements. We have
computed the zero-temperature phase diagram of four different model potentials
with various degrees of core softness. Among the reviewed crystal structures,
there are also a number of non-Bravais lattices, chosen among those observed in
real systems. Some of these crystals are indeed found to be stable for the
selected potentials. We recognize an apparently universal trend for unbounded
potentials, going from high- to low-coordinated crystal phases and back upon
increasing the pressure. Conversely, a bounded repulsion may lead to
intermittent appearance of compact structures with compression and no eventual
settling down in a specific phase. In both cases, the fluid phase repeatedly
reenters at intermediate pressures, as suggested by a cell-theory treatment of
the solids. These findings are of relevance for soft matter in general, but
they also offer fresh insight into the mechanisms subtended to solid
polymorphism in elemental substances.Comment: 16 pages, 5 figures, to be published on Soft Matte
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