896 research outputs found
Structure and dynamics of model colloidal clusters with short-range attractions
We examine the structure and dynamics of small isolated -particle clusters
interacting via short-ranged Morse potentials. "Ideally preprared ensembles"
obtained via exact enumeration studies of sticky hard sphere packings serve as
reference states allowing us to identify key statistical-geometrical properties
and to quantitatively characterize how nonequilibrium ensembles prepared by
thermal quenches at different rates differ from their equilibrium
counterparts. Studies of equilibrium dynamics show nontrival temperature
dependence: nonexponential relaxation indicates both glassy dynamics and
differing stabilities of degenerate clusters with different structures. Our
results should be useful for extending recent experimental studies of small
colloidal clusters to examine both equilibrium relaxation dynamics at fixed
and a variety of nonequilibrium phenomena.Comment: Noro-Frenkel analysis added. Published in PR
Automated tracking of colloidal clusters with sub-pixel accuracy and precision
Quantitative tracking of features from video images is a basic technique
employed in many areas of science. Here, we present a method for the tracking
of features that partially overlap, in order to be able to track so-called
colloidal molecules. Our approach implements two improvements into existing
particle tracking algorithms. Firstly, we use the history of previously
identified feature locations to successfully find their positions in
consecutive frames. Secondly, we present a framework for non-linear
least-squares fitting to summed radial model functions and analyze the accuracy
(bias) and precision (random error) of the method on artificial data. We find
that our tracking algorithm correctly identifies overlapping features with an
accuracy below 0.2% of the feature radius and a precision of 0.1 to 0.01 pixels
for a typical image of a colloidal cluster. Finally, we use our method to
extract the three-dimensional diffusion tensor from the Brownian motion of
colloidal dimers.Comment: 20 pages, 8 figures. Non-revised preprint version, please refer to
http://dx.doi.org/10.1088/1361-648X/29/4/04400
Opposed flow focusing: evidence of a second order jetting transition
We propose a novel microfluidic "opposed-flow" geometry in which the
continuous fluid phase is fed into a junction in a direction opposite the
dispersed phase. This pulls out the dispersed phase into a micron-sized jet,
which decays into micron-sized droplets. As the driving pressure is tuned to a
critical value, the jet radius vanishes as a power law down to sizes below 1
m. By contrast, the conventional "coflowing" junction leads to a first
order jetting transition, in which the jet disappears at a finite radius of
several m, to give way to a "dripping" state, resulting in much larger
droplets. We demonstrate the effectiveness of our method by producing the first
microfluidic silicone oil emulsions with a sub micron particle radius, and
utilize these droplets to produce colloidal clusters
Self-assembly of DNA-coded nanoclusters
We present a theoretical discussion of a self-assembly scheme which makes it
possible to use DNA to uniquely encode the composition and structure of micro-
and nanoparticle clusters. These anisotropic DNA-decorated clusters can be
further used as building blocks for hierarchical self-assembly of larger
structures. We address several important aspects of possible experimental
implementation of the proposed scheme: the competition between different types
of clusters in a solution, possible jamming in an unwanted configuration, and
the degeneracy due to symmetry with respect to particle permutations.Comment: v2, 4 pages, 7 figures, added journal re
Tracking Rotational Diffusion of Colloidal Clusters
We describe a novel method of tracking the rotational motion of clusters of
colloidal particles. Our method utilizes rigid body transfor- mations to
determine the rotations of a cluster and extends conventional proven particle
tracking techniques in a simple way, thus facilitating the study of rotational
dynamics in systems containing or composed of colloidal clusters. We test our
method by measuring dynamical properties of simulated Brownian clusters under
conditions relevant to microscopy experiments. We then use the technique to
track and describe the motions of a real colloidal cluster imaged with confocal
microscopy.Comment: 14 pages, 6 figures. Submitted to Optics Expres
Geometric frustration in small colloidal clusters
We study the structure of clusters in a model colloidal system with competing
interactions using Brownian dynamics simulations. A short-ranged attraction
drives clustering, while a weak, long-ranged repulsion is used to model
electrostatic charging in experimental systems. The former is treated with a
short-ranged Morse attractive interaction, the latter with a repulsive Yukawa
interaction. We consider the yield of clusters of specific structure as a
function of the strength of the interactions, for clusters with m=3,4,5,6,7,10
and 13 colloids. At sufficient strengths of the attractive interaction (around
10 kT), the average bond lifetime approaches the simulation timescale and the
system becomes nonergodic. For small clusters m<=5 where geometric frustration
is not relevant, despite nonergodicity, for sufficient strengths of the
attractive interaction the yield of clusters which maximise the number of bonds
approaches 100%. However for and higher, in the nonergodic regime we find
a lower yield of these structures where we argue geometric frustration plays a
significant role. is a special case, where two structures, of octahedral
and C2v symmetry compete, with the latter being favoured by entropic
contributions in the ergodic regime and by kinetic trapping in the nonergodic
regime. We believe that our results should be valid as far as the one-component
description of the interaction potential is valid. A system with competing
electrostatic repulsions and van der Waals attractions may be such an example.
However, in some cases, the one-component description of the interaction
potential may not be appropriate.Comment: 21 pages, accepted for publication by J. Phys. Condens. Matte
Fabrication of planar colloidal clusters with template-assisted interfacial assembly.
The synthesis of nanoparticle clusters, also referred to as colloidal clusters or colloidal molecules, is being studied intensively as a model system for small molecule interactions as well as for the directed self-assembly of advanced materials. This paper describes a technique for the interfacial assembly of planar colloidal clusters using a combination of top-down lithographic surface modification and bottom-up Langmuir-Blodgett deposition. Micrometer sized polystyrene latex particles were deposited onto a chemically modified substrate from a decane-water interface with Langmuir-Blodgett deposition. The surface of the substrate contained hydrophilic domains of various size, spacing, and shape, while the remainder of the substrate was hydrophobic. Particles selectively deposited onto hydrophilic regions from the decane-water interface. The number of deposited particles depended on the size of each patch, thereby demonstrating that tuning cluster size is possible by engineering patch geometry. Following deposition, the clusters were permanently bonded with temperature annealing and then removed from the substrate via sonication. The permanently bonded planar colloidal clusters were stable in an aqueous environment and at a decane-water interface laden with isotropic colloidal particles. The method is a simple and fast way to synthesize colloidal clusters with few limitations on particle chemistry, composition, and shape.The authors thank Professor Luis M. Liz-Marzan, head of the Colloidal Chemistry Group at Universidade de Vigo, Spain, for the gold nanorod suspension. The research was performed as part of the IAP program MICROMAST financed by BELSPO. The FWO Vlaanderen, projects G.0554.10 and G.0697.11, as well as the ERC starting grant 337739 - HIENA are gratefully acknowledged for their financial support.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/la504383m
Self-assembly of colloidal molecules due to self-generated flow
The emergence of structure through aggregation is a fascinating topic and of
both fundamental and practical interest. Here we demonstrate that
self-generated solvent flow can be used to generate long-range attractions on
the colloidal scale, with sub-pico Newton forces extending into the
millimeter-range. We observe a rich dynamic behavior with the formation and
fusion of small clusters resembling molecules, the dynamics of which is
governed by an effective conservative energy that decays as . Breaking the
flow symmetry, these clusters can be made active
- …