1,052 research outputs found
Self-assembled multi-layer simple cubic photonic crystals of oppositely charged colloids in confinement
Designing and fabricating self-assembled open colloidal crystals have become
one major direction in soft matter community because of many promising
applications associated with open colloidal crystals. However, most of the
self-assembled crystals found in experiments are not open but close-packed.
Here by using computer simulation, we systematically investigate the
self-assembly of oppositely charged colloidal hard spheres confined between two
parallel hard walls, and we find that the confinement can stabilize multi-layer
NaCl-like (simple cubic) open crystals. The maximal layers of stable NaCl-like
crystal increases with decreasing the inverse screening length. More
interestingly, at finite low temperature, the large vibrational entropy can
stabilize some multi-layer NaCl-like crystals against the most energetically
favoured close-packed crystals. In the parameter range studied, we find upto
4-layer NaCl-like crystal to be stable in confinement. Our photonic calculation
shows that the inverse 4-layer NaCl-like crystal can already reproduce the
large photonic band gaps of the bulk simple cubic crystal, which open at low
frequency range with low dielectric contrast. This suggests new possibilities
of using confined colloidal systems to fabricate open crystalline materials
with novel photonic properties
Driving dynamic colloidal assembly using eccentric self-propelled colloids
Designing protocols to dynamically direct the self-assembly of colloidal
particles has become an important direction in soft matter physics because of
the promising applications in fabrication of dynamic responsive functional
materials. Here using computer simulations, we found that in the mixture of
passive colloids and eccentric self-propelled active particles, when the
eccentricity and self-propulsion of active particles are high enough, the
eccentric active particles can push passive colloids to form a large dense
dynamic cluster, and the system undergoes a novel dynamic demixing transition.
Our simulations show that the dynamic demixing occurs when the eccentric active
particles move much faster than the passive particles such that the dynamic
trajectories of different active particles can overlap with each other while
passive particles are depleted from the dynamic trajectories of active
particles. Our results suggest that this is in analogy to the entropy driven
demixing in colloid-polymer mixtures, in which polymer random coils can overlap
with each other while deplete the colloids. More interestingly, we find that by
fixing the passive colloid composition at certain value, with increasing the
density, the system undergoes an intriguing re-entrant mixing, and the demixing
only occurs within certain intermediate density range. This suggests a new way
of designing active matter to drive the self-assembly of passive colloids and
fabricate dynamic responsive materials.Comment: Accepted in Soft Matter. Supplementary information can found at
https://www.dropbox.com/sh/xb3u5iaoucc2ild/AABFUyqjXips7ewaie2rFbj_a?dl=
Non-Equilibrium Strongly Hyperuniform Fluids of Circle Active Particles with Large Local Density Fluctuations
Disordered hyperuniform structures are an exotic state of matter having
vanishing long-wavelength density fluctuations similar to perfect crystals but
without long-range order. Although its importance in materials science has been
brought to the fore in past decades, the rational design of experimentally
realizable disordered strongly hyperuniform microstructures remains
challenging. Here we find a new type of non-equilibrium fluid with strong
hyperuniformity in two-dimensional systems of chiral active particles, where
particles perform independent circular motions of the radius R with the same
handedness. This new hyperuniform fluid features a special length scale, i.e.,
the diameter of the circular trajectory of particles, below which large density
fluctuations are observed. By developing a dynamic mean-field theory, we show
that the large local density fluctuations can be explained as a
motility-induced microphase separation, while the Fickian diffusion at large
length scales and local center-of-mass-conserved noises are responsible for the
global hyperuniformity
Self-Assembled Chiral Photonic Crystals From Colloidal Helices Racemate
Chiral crystals consisting of micro-helices have many optical properties
while presently available fabrication processes limit their large-scale
applications in photonic devices. Here, by using a simplified simulation
method, we investigate a bottom-up self-assembly route to build up helical
crystals from the smectic monolayer of colloidal helices racemate. With
increasing the density, the system undergoes an entropy-driven
co-crystallization by forming crystals of various symmetries with different
helical shapes. In particular, we identify two crystals of helices arranged in
the binary honeycomb and square lattices, which are essentially composed by two
sets of opposite-handed chiral crystal. Photonic calculations show that these
chiral structures can have large complete photonic bandgaps. In addition, in
the self-assembled chiral square crystal, we also find dual polarization
bandgaps that selectively forbid the propagation of circularly polarized lights
of a specific handedness along the helical axis direction. The self-assembly
process in our proposed system is robust, suggesting possibilities of using
chiral colloids to assemble photonic metamaterials.Comment: Accepted in ACS Nan
Privacy protection for RFID-based tracking systems
Abstract—RFID technology is increasingly being deployed in ubiquitous computing environments for object tracking and localization. Existing tracking architecture usually assumes the use of a trusted server which is invulnerable to compromise by internal and external adversaries. However, maintaining such a trusted server is unlikely in the real world. In this paper, we consider the problem of adding privacy protection to object tracking systems built upon passive RFID tags, without relying on a trusted server assumption. Our protocol continues to protect user privacy in the event of partial compromise of a server. I
Non-Equilibrium Structural and Dynamic Behaviors of Polar Active Polymer Controlled by Head Activity
Thermodynamic behavior of polymer chains out of equilibrium is a fundamental
problem in both polymer physics and biological physics. By using molecular
dynamics simulation, we discover a general non-equilibrium mechanism that
controls the conformation and dynamics of polar active polymer, i.e., head
activity commands the overall chain activity, resulting in re-entrant swelling
of active chains and non-monotonic variation of Flory exponent . These
intriguing phenomena lie in the head-controlled railway motion of polar active
polymer, from which two oppose non-equilibrium effects emerge, i.e., dynamic
chain rigidity and the involution of chain conformation characterized by the
negative bond vector correlation. The competition between these two effects
determines the polymer configuration. Moreover, we identify several generic
dynamic features of polar active polymers, i.e., linear decay of the end-to-end
vector correlation function, polymer-size dependent crossover from ballistic to
diffusive dynamics, and a polymer-length independent diffusion coefficient that
is sensitive to head activity. A simple dynamic theory is proposed to
faithfully explain these interesting dynamic phenomena. This sensitive
structural and dynamical response of active polymer to its head activity
provides us a practical way to control active-agents with applications in
biomedical engineering.Comment: 9 pages, 5 figure
Self-Organized Time Crystal in Driven-Dissipative Quantum System
Continuous time crystals (CTCs) are characterized by sustained oscillations
that break the time translation symmetry. Since the ruling out of equilibrium
CTCs by no-go theorems, the emergence of such dynamical phases has been
observed in various driven-dissipative quantum platforms. The current
understanding of CTCs is mainly based on mean-field (MF) theories, which fail
to address the problem of whether the long-range time crystalline order exists
in noisy, spatially extended systems without the protection of all-to-all
couplings. Here, we propose a new kind of CTC realized in a quantum contact
model through self-organized bistability (SOB). The exotic CTCs stem from the
interplay between collective dissipation induced by the first-order absorbing
phase transitions (APTs) and slow constant driving provided by an incoherent
pump. The stability of such oscillatory phases in finite dimensions under the
action of intrinsic quantum fluctuations is scrutinized by the functional
renormalization group method and numerical simulations. Occurring at the edge
of quantum synchronization, the CTC phase exhibits an inherent period and
amplitude with a coherence time diverging with system size, thus also
constituting a boundary time crystal (BTC). Our results serve as a solid route
towards self-protected CTCs in strongly interacting open systems.Comment: 15 pages, 7 figure
Transformable Super-Isostatic Crystals Self-Assembled from Segment Colloidal Rods
Colloidal particles can spontaneously self-assemble into ordered structures,
which not only can manipulate the propagation of light, but also vibration or
phonons. Using Monte Carlo simulation, we study the self-assembly of perfectly
aligned segment rod particles with lateral flat cutting. Under the help of
surface attractions, we find that particles with different cutting degree can
self-assemble into different crystal phases characterized by bond coordination
that varies from 3 to 6. Importantly, we identify a transformable
super-isostatic structures with \emph{pgg} symmetry and redundant bonds
(). We find that this structure can support either the soft bulk model or
soft edge model depending on its Poisson's ratio which can be tuned from
positive to negative by a uniform soft deformation. Importantly, the bulk soft
modes are associated with states of self-stress along the direction of zero
strain during the uniform soft deformation. This self-assembled transformable
super-isostatic structure may act as mechanical metamaterials with potential
application in micro-mechanical engineering.Comment: 11pages,5 figure
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