41 research outputs found
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
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
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
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
Multiple glass transitions in star polymer mixtures: Insights from theory and simulations
The glass transition in binary mixtures of star polymers is studied by mode
coupling theory and extensive molecular dynamics computer simulations. In
particular, we have explored vitrification in the parameter space of size
asymmetry and concentration of the small star polymers at
fixed concentration of the large ones. Depending on the choice of parameters,
three different glassy states are identified: a single glass of big polymers at
low and low , a double glass at high and low
, and a novel double glass at high and high which is
characterized by a strong localization of the small particles. At low
and high there is a competition between vitrification and phase
separation. Centered in the -plane, a liquid lake shows up
revealing reentrant glass formation. We compare the behavior of the dynamical
density correlators with the predictions of the theory and find remarkable
agreement between the two.Comment: 15 figures, to be published in Macromolecule
Partial clustering prevents global crystallization in a binary 2D colloidal glass former
A mixture of two types of super-paramagnetic colloidal particles with long
range dipolar interaction is confined by gravity to a flat interface of a
hanging water droplet. The particles are observed by video microscopy and the
dipolar interaction strength is controlled via an external magnetic field. The
system is a model system to study the glass transition in 2D, and it exhibits
partial clustering of the small particles. This clustering is strongly
dependent on the relative concentration of big and small particles.
However, changing the interaction strength reveals that the clustering
does not depend on the interaction strength. The partial clustering scenario is
quantified using Minkowski functionals and partial structure factors. Evidence
that partial clustering prevents global crystallization is discussed