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We explore the growth of two-dimensional quasicrystals, i.e., aperiodic structures that possess long-range order, from two seeds at various distances and with different orientations by using dynamical phase-field crystal calculations. We compare the results to the growth of periodic crystals from two seeds. There, a domain border consisting of dislocations is observed in case of large distances between the seed and large angles between their orientation. Furthermore, a domain border is found if the seeds are placed at a distance that does not fit to the periodic lattice. In the case of the growth of quasicrystals, we only observe domain borders for large distances and different orientations. Note that all distances do inherently not match to a perfect domain wall-free quasicrystalline structure. Nevertheless, we find dislocation-free growth for all seeds at a small enough distance and for all seeds that approximately have the same orientation. In periodic structures, the stress that occurs due to incommensurate distances between the seeds results in phononic strain fields or, in the case of too large stresses, in dislocations. In contrast, in quasicrystals an additional phasonic strain field can occur and suppress dislocations. Phasons are additional degrees of freedom that are unique to quasicrystals. As a consequence, the additional phasonic strain field helps to distribute the stress and facilitates the growth of dislocation-free quasicrystals from multiple seeds. In contrast, in the periodic case the growth from multiple seeds most likely leads to a structure with multiple domains. Our work lays the theoretical foundations for growing perfect quasicrystals from different seeds and is therefore relevant for many applications. [ABSTRACT FROM AUTHOR]

Stochastic equations of the hydrodynamic theory of plasma are presented in relation to strong external fields. It is shown that the use of these stochastic equations makes it possible to obtain new theoretical solutions for plasma as a result of its heating in a strong external electric field. Theoretical solutions for the conductivity of turbulent plasma when heated in an external electric field of 100 V/cm are considered. Calculated values for the electron drift velocity, electron mobility, electron collision frequency, and the Coulomb logarithm in the region of strong electric fields are obtained. Here we consider experiments on turbulent heating of hydrogen plasma in the range of electric field strength of 100 < E < 1000. The calculated dependences of plasma conductivity are in satisfactory agreement with experimental data for heating plasma in a strong electric field. It is shown that the plasma turbulence in the region of strong electric fields E ~1000 V/cm is close to 100%. For the first time, it is confirmed that the derived dependences for collision frequency, drift velocity, and other values include the degree of turbulence of plasma, which makes it possible to correctly describe experimental data for heating plasma even with strong electric fields. In addition, it was determined that the scatter of experimental data may be associated with the variability of the function in the expression for the heat flux density. For the first time, it is shown theoretically that the experimentally determined fact of the possibility of the existence of an approximate constancy of plasma conductivity in the region E = 100–1000 V/cm can occur with an error of ~30%. The results show significant advantages of the stochastic hydrodynamic plasma theory over other methods that are not yet able to satisfactorily as well as qualitatively and quantitatively predict long-known experimental data while taking into account the degree of turbulence. [ABSTRACT FROM AUTHOR]

We analyze the effect of polydispersity in the arm number on the effective interactions, structural correlations, and phase behavior of star polymers in a good solvent. The effective interaction potential between two star polymers with different arm numbers is derived using scaling theory. The resulting expression is tested against monomer-resolved molecular dynamics simulations. We find that the theoretical pair potential is in agreement with the simulation data in a much wider polydispersity range than other proposed potentials. We then use this pair potential as an input in a many-body theory to investigate polydispersity effects on the structural correlations and the phase diagram of dense star polymer solutions. In particular, we find that a polydispersity of 10%, which is typical in experimental samples, does not significantly alter previous findings for the phase diagram of monodisperse solutions.

We show that the structure of a substrate pattern drastically influences the nature of surface freezing. By using phenomenological theory and computer simulations of a hard sphere fluid next to a substrate formed by a periodic array of fixed spheres, we find that a pattern which is commensurate with the bulk crystal induces complete surface freezing through a cascade of layering transitions. A rhombic pattern, on the other hand, either generates a crystalline sheet which is unstable as a bulk phase or prohibits surface freezing completely.

Using computer simulations we investigate the microscopic structure of the singular director field within a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders. To induce an overall topological charge, the particles are either confined to a two-dimensional circular cavity with homeotropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit half-integer topological point defects. The isotropic defect core has a radius of the order of one particle length and is surrounded by free-standing density oscillations. The effective interaction between two defects is investigated. All results should be experimentally observable in thin sheets of colloidal liquid crystals.

Penetrable spheres have been the object of recent extensive investigations as a prototype for intermicellar interactions in a solvent, and as representing a class of bounded potentials allowing complete interpenetrability of the particles. Here we compare density-functional and simulation results for the pair-correlation functions in a bulk fluid of penetrable spheres, as a stringent test for the approximation of "universality" of the bridge functional. Considering either a fundamental-measure functional for penetrable spheres or a perturbative treatment using a fundamental-measure hard-sphere functional, we conclude that hard-sphere-type bridge functionals are applicable also for bounded potentials with high penetrability.

We present a density functional theory for mixtures of (hard sphere) colloidal particles and ideal polymers. For this extreme nonadditive system we employ a fundamental measures approach to construct a functional which incorporates the correct dimensional crossover and the exact low density limit. In bulk fluid mixtures the functional yields the same free energy and, therefore, the same gas-liquid (demixing) transition as given by free-volume theory. It generates consistent pair correlation functions; the partial structure factors S(ij)(k) diverge, as k-->0, at the critical point obtained from the free energy. Our results for the structure agree well with those from simulation and Percus-Yevick theory.

We propose a statistical mechanical model for colloidal particles suspended in an emulsion of liquid droplets. The particles are modeled as hard spheres. The interaction between droplets is also hard, but the particles are able to penetrate the droplets. A swelling of droplets is taken into account to ensure material conservation of the droplet liquid. Hence the presence of the colloids generates droplet polydispersity. Using computer simulation and liquid state theory, we find that the relative polydispersity exhibits nonmonotonic behavior as a function of the particle packing fraction and can be traced back to hard sphere bulk density fluctuations.

Inertial underdamped collisions preserve the memory of physical parameters that existed before the collision, leading to phenomena usually unseen in overdamped systems. Here we probe the less studied inertial chiral matter with spinners on an air table. We show here the emergence of high levels of spin for a minority of (+) handed spinners in the presence of a majority of (−) handed spinners (vice versa). This deep violation of equipartition occurs due to the inertial (memory preserving) nature of elastic collisions between underdamped translating and rotating objects. Underdamped spinners of the same spin sign annihilate their spins when they elastically collide, transferring their spin angular momentum into orbital angular momentum, while oppositely handed spinners tend to preserve their individual spin levels, leading to the pumping of minority spinners to high spin levels. Entropy production and the flow of entropy in this underdamped system are also counter-intuitive, showing dramatic oscillations in time. By studying inertial spinners on an air table with different ratios between counterclockwise and clockwise species, the authors found that underdamped chiral spinners display phenomena usually unseen in overdamped chiral spinners. These include higher energy pumped into the minority species and oscillatory entropy when one species dominates the other. [ABSTRACT FROM AUTHOR]

Zebrafish constitute a convenient laboratory–based biological system for studying collective behavior. It is possible to interpret a group of zebrafish as a system of interacting agents and to apply methods developed for the analysis of systems of active and even passive particles. Here, we consider the effect of group size. We focus on two– and many–body spatial correlations and dynamical order parameters to investigate the multistate behavior. For geometric reasons, the smallest group of fish which can exhibit this multistate behavior consisting of schooling, milling and swarming is three. We find that states exhibited by groups of three fish are similar to those of much larger groups, indicating that there is nothing more than a gradual change in weighting between the different states as the system size changes. Remarkably, when we consider small groups of fish sampled from a larger group, we find very little difference in the occupancy of the state with respect to isolated groups, nor is there much change in the spatial correlations between the fish. This indicates that fish interact predominantly with their nearest neighbors, perceiving the rest of the group as a fluctuating background. Therefore, the behavior of a crowd of fish is already apparent in groups of three fish. Active matter systems, such as zebrafish groups, demonstrate similar collective dynamics to assemblies of particles, or interacting agents. The authors show that majority of dynamics patterns seen in large zebrafish groups are exhibited by a minimal group of three fish. [ABSTRACT FROM AUTHOR]

It is well known that molecules confined very close to a surface arrange into molecular layers. Because solid-liquid interfaces are ubiquitous in the chemical, biological and physical sciences, it is crucial to develop methods to easily access molecular layers and exploit their distinct properties by producing molecular layered crystals. Here we report a method based on crystallization in ultra-thin puddles enabled by gas blowing, which allows to produce molecular layered crystals with thickness down to the monolayer onto a surface, making them directly accessible for characterization and further processing. By selecting four molecules with different types of polymorphs, we observed exclusive crystallization of polymorphs with Van der Waals interlayer interactions, which have not been observed with traditional confinement methods. In conclusion, the gas blowing approach unveils the opportunity to perform materials chemistry under confinement onto a surface, enabling the formation of distinct crystals with selected polymorphism. Molecules arranged in close proximity to a surface form molecular layers, exhibiting distinct properties. However, the creation of these layers is challenging. Here, the authors present a technique for generating molecular layers through crystallization induced by gas blowing onto a surface. [ABSTRACT FROM AUTHOR]

There are many processes in cell biology that can be modelled in terms of an actively switching particle. The continuous degrees of freedom of the particle evolve according to a hybrid stochastic differential equation whose drift term depends on a discrete internal or environmental state that switches according to a continuous time Markov chain. Examples include Brownian motion in a randomly switching environment, membrane voltage fluctuations in neurons, protein synthesis in gene networks, bacterial run-and-tumble motion, and motor-driven intracellular transport. In this paper we derive generalized Dean–Kawasaki (DK) equations for a population of actively switching particles, either independently switching or subject to a common randomly switching environment. In the case of a random environment, we show that the global particle density evolves according to a hybrid DK equation. Averaging with respect to the Gaussian noise processes in the absence of particle interactions yields a hybrid partial differential equation for the one-particle density. We use this to show how a randomly switching environment induces statistical correlations between the particles. We also discuss methods for handling the moment closure problem for interacting particles, including dynamical density functional theory and mean field theory. We then develop the analogous constructions for independently switching particles. In order to derive a DK equation, we introduce a discrete set of global densities that are indexed by the single-particle internal states, and take expectations with respect to the switching process. However, the resulting DK equation is no longer closed when particle interactions are included. We conclude by deriving Martin–Siggia–Rose–Janssen–de Dominicis path integrals for the global density equations in the absence of interactions, and relate this to recent field theoretic studies of Brownian gases and run-and-tumble particles. [ABSTRACT FROM AUTHOR]

We derive a bound for entropy production in terms of the mean of normalizable path-antisymmetric observables. The optimal observable for this bound is shown to be the signum of entropy production, which is often easier determined or estimated than entropy production itself. It can be preserved under coarse graining by the use of a simple path grouping algorithm. We demonstrate this relation and its properties using a driven network on a ring, for which the bound saturates for short times for any driving strength. This work can open a way to systematic coarse graining of entropy production. [ABSTRACT FROM AUTHOR]

Here, we report the results of qualitative and quantitative investigations of the first-order phase transition in the ionic liquid 1-ethylpyridinium triflate exhibiting a high variability of temperature ranges, within which the freezing and melting occur. By two methods, the direct fast quenching/annealing and the slow temperature-controlled differential scanning calorimeter, it is revealed that despite the almost constant absolute enthalpies of phase transition, the freezing occurs faster with the larger temperature contrast (cooling rate) between the initially hotter sample and the colder surrounding. This feature is a clear exhibition of the Mpemba effect. The regularity in the change of the melting point is analyzed as well. [ABSTRACT FROM AUTHOR]

Given that pectin is a well-known substance used for drug delivery, we aimed to obtain and further examine the efficacy of interpolyelectrolyte complexes based on citrus or apple pectin and the Eudragit® EPO for using these carriers in oral drug delivery. To characterize the physicochemical properties of these compounds, turbidity, gravimetry, viscosity, elementary analysis, FTIR spectroscopy, and DSC analysis were utilized. Diffusion transport characteristics were evaluated to assess the swelling ability of the matrices and the release of diclofenac sodium. To examine the release parameters, mathematical modeling was performed by using the Korsmayer–Peppas and Logistic equations as well. During the turbidity study, stoichiometry compositions were selected for the developed IPECs EPO/PecA and EPO/PecC at pH values = 4.0, 5.0, 6.0, and 7.0. The FTIR spectra of the complexes were characterized by an increase in the intensity of the bands at 1610 cm−1 and 1400 cm−1. According to the DSC analysis, IPEC has a certain Tg = 57.3 °C. The highest release rates were obtained for IPEC EPO/PecC_1 and EPO/PecC_4. The mechanism of drug transport from the matrices IPEC EPO/PecC, IPEC EPO/PecA_3, and EPO/PecA_4 can be characterized as Super Case II. Anomalous release (non-Fickian release) is typical for IPEC EPO/PecA_1 and EPO/PecA_2. Thus, the resulting systems can be further used for the effective delivery of the drugs to the colon. [ABSTRACT FROM AUTHOR]

Fracturing fluid property play a critical role in developing unconventional reservoirs. Deep eutectic solvents (DESs) show fascinating potential for property improvement of clean fracturing fluids (CFFs) due to their low-price, low-toxicity, chemical stability and flexible designability. In this work, DESs were synthesized by mixing hydrogen bond acceptors (HBAs) and a given hydrogen bond donor (HBD) to explore their underlying influence on CFF properties based on the intermolecular interactions. The hydrogen-bonding, van der Waals and electrostatic interactions between DES components and surfactants improved the CFF properties by promoting the arrangement of surfactants at interface and enhancing the micelle network strength. The HBD enhanced the resistance of CFF for Ca2+ due to coordination-bonding interaction. The DESs composed of choline chloride (ChCl) and malonic acid show great enhancement for surface, rheology, temperature resistance, salt tolerance, drag reduction, and gel-breaking performance of CFFs. The DESs also improved the gel-breaking CFF-oil interactions, increasing the imbibition efficiencies to 44.2% in 74 h. Adjusting HBAs can effectively strengthen the intermolecular interactions (e.g., HBA-surfactant and HBD-surfactant interactions) to improve CFF properties. The DESs developed in this study provide a novel strategy to intensify CFF properties. [ABSTRACT FROM AUTHOR]

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Swarms of self-propelled micromotors can mimic the processes of natural systems and construct artificial intelligent materials to perform complex collective behaviors. Compared to self-propelled Janus micromotors, the isotropic colloid motors, also called micromotors or microswimmers, have advantages in self-assembly to form micromotor swarms, which are efficient in resistance to external disturbance and the delivery of large quantity of cargos. In this minireview, we summarize the fundamental principles and interactions for the assembly of isotropic active particles to generate micromotor swarms. Recent discoveries based on either catalytic or external physical field-stimulated micromotor swarms are also presented. Then, the strategy for the reconstruction and motion control of micromotor swarms in complex environments, including narrow channels, maze, raised obstacles, and high steps/low gaps, is summarized. Finally, we outline the future directions of micromotor swarms and the remaining challenges and opportunities. [ABSTRACT FROM AUTHOR]

Understanding particle motion in narrow channels can guide progress in numerous applications, from filtration to vascular transport. Thermal or active fluctuations of fluid-filled channel walls can slow down or increase the dispersion of tracer particles via entropic trapping in the wall bulges or hydrodynamic flows induced by wall fluctuations, respectively. Previous studies concentrated primarily on the case of a single Brownian tracer. Here, we address what happens when there is a large ensemble of interacting Brownian tracers – a common situation in applications. Introducing repulsive interactions between tracer particles, while ignoring the presence of a background fluid, leads to an effective flow field. This flow field enhances tracer dispersion, a phenomenon reminiscent of that seen for single tracers in incompressible background fluid. We characterise the dispersion by the long-time diffusion coefficient of tracers numerically and analytically with a mean-field density functional analysis. We find a surprising effect where an increased particle density enhances the diffusion coefficient, challenging the notion that crowding effects tend to reduce diffusion. Here, inter-particle interactions push particles closer to the fluctuating channel walls. Interactions between the fluctuating wall and the now-nearby particles then drive particle mixing. Our mechanism is sufficiently general that we expect it to apply to various systems. In addition, our perturbation theory quantifies dispersion in generic advection–diffusion systems. [ABSTRACT FROM AUTHOR]