9 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
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
Pattern formation in two-dimensional square-shoulder systems
Using a highly efficient and reliable optimization tool that is based on ideas of genetic algorithms, we have systematically studied the pattern formation of the two-dimensional square-shoulder system. An overwhelming wealth of complex ordered equilibrium structures emerge from this investigation as we vary the shoulder width. With increasing pressure three structural archetypes could be identified: cluster lattices, where clusters of particles occupy the sites of distorted hexagonal lattices, lane formation, and compact particle arrangements with high coordination numbers. The internal complexity of these structures increases with increasing shoulder width. 1