15 research outputs found
Monte-Carlo simulation of string-like colloidal assembly
We study structural phase transition of polymer-grafted colloidal particles
by Monte Carlo simulations on hard spherical particles. The interaction
potential, which has a weak repulsive step outside the hard core, was validated
with use of the self-consistent field calculations. With this potential,
canonical Monte Carlo simulations have been carried out in two and three
dimensions using the Metropolis algorithm. At low temperature and high density,
we find that the particles start to self-assemble and finally align in strings.
By analyzing the cluster size distribution and string length distribution, we
construct a phase diagram and find that this string-like assembly is related to
the percolation phenomena. The average string length diverges in the region
where the melting transition line and the percolation transition line cross,
which is similar to Ising spin systems where the percolation transition line
and the order-disorder line meet on the critical point.Comment: 7 pages, 6 figures, Accepted for Europhysics Letter
Particle Monte Carlo simulation of string-like colloidal assembly in 2 dimensions
We simulate structural phase behavior of polymer-grafted colloidal particles
by molecular Monte Carlo technique. Interparticle potential, which has a finite
repulsive square-step outside a rigid core of the colloid, was previously
confirmed via numerical self-consistent field calculation. This model potential
is purely repulsive. We simulate these model colloids in the canonical ensemble
in 2 dimensions and find that these particles containing no interparticle
attraction self-assemble and align in a string-like assembly, at low
temperature and high density. This string-like colloidal assembly is related to
percolation phenomena. Analyzing the cluster size distribution and the average
string length, we build phase diagrams and discover that the average string
length diverges around the region where the melting transition line and the
percolation transition line cross. This result is similar to Ising spin
systems, in which the percolation transition line and the order-disorder line
meet at a critical point.Comment: 11 pages, 14 figure
Molecular simulation of 2-dimensional microphase separation of single-component homopolymers grafted onto a planar substrate
The structural phase behavior of polymer brushes, single-component linear
homopolymers grafted onto a planar substrate, is studied using the molecular
Monte Carlo method in 3 dimensions. When simulation parameters of the system
are set in regions of macrophase separation of solution for the corresponding
non-grafted homopolymers, the grafted polymers also prefer segregation.
However, macrophase separation is disallowed due to the spatially-fixed
grafting points of the polymers. Such constraints on the grafting are similar
to connecting points between blocks of non-grafted diblock copolymers at the
microphase separation in the melt state. This results in "microphase
separation" of the homopolymer brush in the lateral direction of the substrate.
Here we extensively search the parameter space and reveal various lateral
domain patterns that are similar to those found in diblock copolymer melts at
microphase separation.Comment: 6 pages, 5 figures, accepted for publication in EP
Soft Spheres Make More Mesophases
We use both mean-field methods and numerical simulation to study the phase
diagram of classical particles interacting with a hard-core and repulsive, soft
shoulder. Despite the purely repulsive interaction, this system displays a
remarkable array of aggregate phases arising from the competition between the
hard-core and shoulder length scales. In the limit of large shoulder width to
core size, we argue that this phase diagram has a number of universal features,
and classify the set of repulsive shoulders that lead to aggregation at high
density. Surprisingly, the phase sequence and aggregate size adjusts so as to
keep almost constant inter-aggregate separation.Comment: 4 pages, 2 included 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
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