3,242 research outputs found
Nonequilibrium adsorption of 2AnB patchy colloids on substrates
We study the irreversible adsorption of spherical patchy colloids
(with two -patches on the poles and -patches along the equator) on a
substrate. In particular, we consider dissimilar , , and binding
probabilities. We characterize the patch-colloid network and its dependence on
and on the binding probabilities. Two growth regimes are identified with
different density profiles and we calculate a growth mode diagram as a function
of the colloid parameters. We also find that, close to the substrate, the
density of the network, which depends on the colloid parameters, is
characterized by a depletion zone
Nonequilibrium self-organization of colloidal particles on substrates: adsorption, relaxation, and annealing
Colloidal particles are considered ideal building blocks to produce materials
with enhanced physical properties. The state-of-the-art techniques for
synthesizing these particles provide control over shape, size, and
directionality of the interactions. In spite of these advances, there is still
a huge gap between the synthesis of individual components and the management of
their spontaneous organization towards the desired structures. The main
challenge is the control over the dynamics of self-organization. In their
kinetic route towards thermodynamically stable structures, colloidal particles
self-organize into intermediate (mesoscopic) structures that are much larger
than the individual particles and become the relevant units for the dynamics.
To follow the dynamics and identify kinetically trapped structures, one needs
to develop new theoretical and numerical tools. Here we discuss the
self-organization of functionalized colloids (also known as patchy colloids) on
attractive substrates. We review our recent results on the adsorption and
relaxation and explore the use of annealing cycles to overcome kinetic barriers
and drive the relaxation towards the targeted structures
Adsorbed films of three-patch colloids: Continuous and discontinuous transitions between thick and thin films
We investigate numerically the role of spatial arrangement of the patches on
the irreversible adsorption of patchy colloids on a substrate. We consider
spherical three-patch colloids and study the dependence of the kinetics on the
opening angle between patches. We show that growth is suppressed below and
above minimum and maximum opening angles, revealing two absorbing phase
transitions between thick and thin film regimes. While the transition at the
minimum angle is continuous, in the Directed Percolation class, that at the
maximum angle is clearly discontinuous. For intermediate values of the opening
angle, a rough colloidal network in the Kardar-Parisi-Zhang universality class
grows indefinitely. The nature of the transitions was analyzed in detail by
considering bond flexibility, defined as the dispersion of the angle between
the bond and the center of the patch. For the range of flexibilities considered
we always observe two phase transitions. However, the range of opening angles
where growth is sustained increases with flexibility. At a tricritical
flexibility, the discontinuous transition becomes continuous. The practical
implications of our findings and the relation to other nonequilibrium
transitions are discussed
Kinetic interfaces of patchy particles
We study the irreversible adsorption of patchy particles on substrates in the
limit of advective mass transport. Recent numerical results show that the
interface roughening depends strongly on the particle attributes, such as,
patch-patch correlations, bond flexibility, and strength of the interactions,
uncovering new absorbing phase transitions. Here, we revisit these results and
discuss in detail the transitions. In particular, we present new evidence that
the tricritical point, observed in systems of particles with flexible patches,
is in the tricritical directed percolation universality class. A scaling
analysis of the time evolution of the correlation length for the aggregation of
patchy particles with distinct bonding energies confirms that the critical
regime is in the Kardar-Parisi-Zhang with quenched disorder universality class
Annealing cycles and the self-organization of functionalized colloids
The self-assembly of functionalized (patchy) particles with directional
interactions into target structures is still a challenge, despite the
significant experimental advances on their synthesis. The self-assembly
pathways are typically characterized by high energy barriers that hinder the
access to stable (equilibrium) structures. A possible strategy to tackle this
challenge is to perform annealing cycles. By periodically switching on and off
the inter-particle bonds, one expects to smooth-out the kinetic pathways and
favor the assembly of targeted structures. Preliminary results have shown that
the efficiency of annealing cycles depends strongly on their frequency. Here,
we study numerically how this frequency-dependence scales with the strength of
the directional interactions (size of the patch ). We use analytical
arguments to show that the scaling results from the statistics of a random walk
in configurational space
Dynamics of patchy particles in and out of equilibrium
We combine particle-based simulations, mean-field rate equations, and
Wertheim's theory to study the dynamics of patchy particles in and out of
equilibrium, at different temperatures and densities. We consider an initial
random distribution of non-overlapping three-patch particles, with no bonds,
and analyze the time evolution of the breaking and bonding rates of a single
bond. We find that the asymptotic (equilibrium) dynamics differs from the
initial (out of equilibrium) one. These differences are expected to depend on
the initial conditions, temperature, and density
Active nematic-isotropic interfaces in channels
We use numerical simulations to investigate the hydrodynamic behavior of the
interface between nematic (N) and isotropic (I) phases of a confined active
liquid crystal. At low activities, a stable interface with constant shape and
velocity is observed separating the two phases. For nematics in homeotropic
channels, the velocity of the interface at the NI transition increases from
zero (i) linearly with the activity for contractile systems and (ii)
quadratically for extensile ones. Interestingly, the nematic phase expands for
contractile systems while it contracts for extensile ones, as a result of the
active forces at the interface. Since both activity and temperature affect the
stability of the nematic, for active nematics in the stable regime the
temperature can be tuned to observe static interfaces, providing an operational
definition for the coexistence of active nematic and isotropic phases. At
higher activities, beyond the stable regime, an interfacial instability is
observed for extensile nematics. In this regime defects are nucleated at the
interface and move away from it. The dynamics of these defects is regular and
persists asymptotically for a finite range of activities. We used an improved
hybrid model of finite differences and lattice Boltzmann method with
multi-relaxation-time collision operator, the accuracy of which allowed us to
characterize the dynamics of the distinct interfacial regimes.Comment: 11 pages, 13 figure
Optimal number of linkers per monomer in linker-mediated aggregation
We study the dynamics of diffusion-limited irreversible aggregation of
monomers, where bonds are mediated by linkers. We combine kinetic Monte Carlo
simulations of a lattice model with a mean-field theory to study the dynamics
when the diffusion of aggregates is negligible and only monomers diffuse. We
find two values of the number of linkers per monomer which maximize the size of
the largest aggregate. We explain the existence of the two maxima based on the
distribution of linkers per monomer. This observation is well described by a
simple mean-field model. We also show that a relevant parameter is the ratio of
the diffusion coefficients of monomers and linkers. In particular, when this
ratio is close to ten, the two maxima merge at a single maximum
The random field Blume-Capel model revisited
We have revisited the mean-field treatment for the Blume-Capel model under
the presence of a discrete random magnetic field as introduced by Kaufman and
Kanner. The magnetic field () versus temperature () phase diagrams for
given values of the crystal field were recovered in accordance to Kaufman
and Kanner original work. However, our main goal in the present work was to
investigate the distinct structures of the crystal field versus temperature
phase diagrams as the random magnetic field is varied because similar models
have presented reentrant phenomenon due to randomness. Following previous works
we have classified the distinct phase diagrams according to five different
topologies. The topological structure of the phase diagrams is maintained for
both and cases. Althoug the phase diagrams exhibit a richness of
multicritical phenomena we did not found any reentrant effect as have been seen
in similar models.Comment: 21 pages, 5 figure
Field-driven dynamical demixing of binary mixtures
We consider mixtures of two species of spherical colloidal particles that
differ in their hydrodynamic radii, but are otherwise identical, in the
presence of an external field. Since the particle-particle and particle-field
interactions are the same for both species, they are completely mixed in the
thermodynamic limit in the presence of any static field. Here, we combine
Brownian Dynamics and Dynamic Density Functional theory of fluids to show that
for sufficiently large differences in the hydrodynamic radius of the particles
(and corresponding differences in their electrophoretic mobilities) dynamical
demixing is observed. These demixed states are transient but, under certain
conditions, packing effects compromise the relaxation towards the thermodynamic
states and the lifetime of the demixed phases increases significantly
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