Self-organization Of Particles Research Articles

Self-organization of particles in the superionic phase of lanthanum trifluoride

When a laser beam (λ = 396.3 nm) propagates through a nonuniformly heated superionic LaF3 crystal in the direction of lattice constant c, alternating bright and dark fringes arise on the screen. The fringes run from the warmer face to the colder one. The number and width of the fringes are found to depend on the temperature gradient in the crystal: the smaller (greater) the temperature difference between the faces, the smaller (greater) the number of moving fringes. It is the author’s opinion that this effect is due to the wave transfer of applied heat and reflects the self-organization and collective displacements of the ions of the “quasi-liquid” sublattice in a nonuniform temperature field. A qualitative model of heat wave transfer in the LaF3 superionic phase is suggested.

Experimental Design Applied to Spin Coating of 2D Colloidal Crystal Masks: A Relevant Method?

Monolayers of colloidal spheres are used as masks in nanosphere lithography (NSL) for the selective deposition of nanostructured layers. Several methods exist for the formation of self-organized particle monolayers, among which spin coating appears to be very promising. However, a spin coating process is defined by several parameters like several ramps, rotation speeds, and durations. All parameters influence the spreading and drying of the droplet containing the particles. Moreover, scientists are confronted with the formation of numerous defects in spin coated layers, limiting well-ordered areas to a few micrometers squared. So far, empiricism has mainly ruled the world of nanoparticle self-organization by spin coating, and much of the literature is experimentally based. Therefore, the development of experimental protocols to control the ordering of particles is a major goal for further progress in NSL. We applied experimental design to spin coating, to evaluate the efficiency of this method to extract and model the relationships between the experimental parameters and the degree of ordering in the particles monolayers. A set of experiments was generated by the MODDE software and applied to the spin coating of latex suspension (diameter 490 nm). We calculated the ordering by a homemade image analysis tool. The results of partial least squares (PLS) modeling show that the proposed mathematical model only fits data from strictly monolayers but is not predictive for new sets of parameters. We submitted the data to principal component analysis (PCA) that was able to explain 91% of the results when based on strictly monolayered samples. PCA shows that the ordering was positively correlated to the ramp time and negatively correlated to the first rotation speed. We obtain large defect-free domains with the best set of parameters tested in this study. This protocol leads to areas of 200 μm(2), which has never been reported so far.

Dispersions of multi-walled carbon nanotubes in liquid crystals: A physical picture of aggregation

Aggregation of carbon nanotubes dispersed in nematic liquid crystalline medium is discussed. A model assuming that the aggregates consist of a “skeleton” formed by stochastically arranged nanotubes and a “shell” (“coat”) of incorporated and adjacent nematic molecules is proposed. The aggregates of this type can be considered as large quasi-macroscopic particles in the nematic matrix. The resulting composite system is a representative of a new type of complex molecular liquids with self-organization of particles in anisotropic medium. Many essential features and implications of the theoretical model (e.g., effect of concentration, aspect ratio and orientational order parameter of the nanotubes on the size and fractal dimensionality of the aggregates formed, as well as on the rate of aggregation) are in good agreement with experimental data obtained by various physical methods.

移流集積法を利用した多様な自己組織化粒子膜の発現とその構造制御

Significant progress has been made in techniques of surface patterning over large areas; complex patterns of particles can be formed using predefined templates or soft lithography. Although these approaches are quite effective, the use of template-free self-organization processes becomes necessary to complement them as the required structure sizes become of the order of nanometers. The advantages of a self-organization technique are its simplicity, versatility, cost-effectiveness, and compatibility with heterogeneous integration processes.In this paper, we present our recent results on the pattern formation of colloidal particles by using a template-free technique based on the self-organization of particles. Our technique can produce various patterns including stripes, dot arrays, grids, and Sierpinski triangles.

Structural stability and jamming of self-organized cluster conformations in dense granular materials

We examine emergent, self-organized particle cluster conformations in quasistatically deforming dense granular materials from the perspective of structural stability. A structural mechanics approach is employed, first, to devise a new stability measure for such conformations in equilibrium and, second, to use this measure to explore the evolving stability of jammed states of specific cluster conformations, i.e. particles forming force chains and minimal contact cycles. Knowledge gained on (a) the spatial and temporal evolution of stability of individual jammed conformations and (b) their relative stability levels, offer valuable clues on the rheology and, in particular, self-assembly of granular materials. This study is undertaken using data from assemblies of nonuniformly sized circular particles undergoing 2D deformation in two biaxial compression tests: a discrete element simulation of monotonic loading under constant confining pressure, and cyclic loading of a photoelastic disk assembly under constant volume. Our results suggest that the process of self-assembly in these systems is realized at multiple length scales, and that jammed force chains and minimal cycles form the basic building blocks of this process. In particular, 3-cycles are stabilizing agents that act as granular trusses to the load-bearing force chain columns. This co-evolutionary synergy between force chains and 3-cycles proved common to the different materials under different loading conditions. Indeed, the remarkable similarities in the evolution of stability, prevalence and persistence of minimal cycles and force chains in these systems suggest that these structures and their co-evolution together form a generic feature of dense granular systems under quasistatic loading.

Nanoscale topography of hepatitis B antigen particles by atomic force microscopy

Hepatitis B virus envelope is mainly composed of three forms of the same protein expressed from different start codons of the same open reading frame. The smaller form named S protein corresponds to the C-terminal common region and represents about 80% of the envelope proteins. It is mainly referred as hepatitis B virus surface antigen (HBsAg). Over expressed in the host cell, this protein can be produced as spherical and tubular self-organized particles. Highly immunogenic, these particles are used in licensed hepatitis B vaccines. In this study we have combined transmission electron microscopy and atomic force microscopy to determine the shape and size of HBsAg particles produced from the yeast Hansenula polymorpha. Tapping mode atomic force microscopy in liquid allows structural details of the surface to be delineated with a resolution in the nanometer range. Particles were decorated by closely packed spike-like structures protruding from particle surface. Protrusions appeared uniformly distributed at the surface and an average number of 75 protrusions per particle were calculated. Importantly, we demonstrated that proteins mainly contribute to the topography of the protrusions.

Self-organization of particles in an evaporating meniscus of a colloidal solution

The nature of the self-oscillations of shape that occur in a meniscus of an evaporating colloidal solution (or a microdrop) is investigated. The concentration self-oscillations resulting in the formation of a solid film with a periodic and jumpwise decreasing thickness are considered.

Self-Organization of Particles with Planar Surface Anchoring in a Cholesteric Liquid Crystal

We present birefringence and fluorescence confocal microscopy studies of melamine particles in a liquid-crystalline host solvent. The liquid crystal has a cholesteric phase at room temperature with a helical pitch that can be modified by changing the composition. The pitch employed here is always less than the particle diameter (3 microm). We demonstrate via birefringence that the mesogens preferentially anchor flat at the melamine surface. Via studies in a sample cell with aligning surfaces we show that although the particles form chains in a nematic liquid crystal they organize in 2D plates in a cholesteric. Fluorescence confocal microscopy and particle location analysis are used to determine the radial distribution function and to evaluate the particle aggregation number as a function of pitch length. We discuss possible explanations for the self-organization.

Concentration effects in mesoscopic simulation of coarsening

The self-organization of particles in a two-phase system in the coexistence region through a diffusive mechanism is known as Ostwald ripening. A mesoscopic model derived from the spin exchange Ising model is used here in a computational study of Ostwald ripening. The typical cluster size is observed to grow like Lifshitz–Slyozov growth law over an early range of times with faster growth at later times. The effect of changing the concentration of particles on the morphological evolution of the system is also discussed.

Correlated response in a driven flow of self-organizing particles around a slit in porous media by interacting lattice gas

The flow of immiscible particles (A, B) through a porous medium with a vertical slit is studied by an interacting lattice-gas computer simulation on a discrete lattice. The source of the particles is connected to the bottom and particles are driven upward by concentration gradient and a pressure bias against gravity. Distribution of flowing particles around the slit is examined as a function of the slit width and bias at high and low porosity at a steady state. At the low bias, a sharp change in the densities (high in slit to low in adjacent porous media) of both constituents occurs as expected. Onset of an undershooting in the density and mobility of particle profiles appears at the interface of slit and the porous medium on increasing the bias, an unexpected correlated response. The competition between the faster flow in the slit and slower motion of the particles in the surrounding porous medium induces stronger correlations at higher bias; as a result, a well-defined density profile emerges with higher density in the porous matrix away from the slit interface. The range of correlation and therefore the response increases on increasing the bias. Lowering the porosity to near the percolation threshold leads to the onset of oscillation in the density profile and broadening of the mobility profile, a distinct difference from the response at high porosity.

Temporal evolution of self-organization of gelatin molecules and clusters on quartz surface

Aqueous gelatin solutions when spread on hydrophilic substrates form self-organized structures where the gelatin molecules and clusters are arranged as self-similar objects giving a mass fractal dimension df=1.67 and 1.72 for solutions made with KCl and NaCl salts as estimated from atomic force microscopic studies. The dehydration driven self-organization of particles changed the df values to 1.78 and 1.81, respectively, after 24 h. This further changed to 1.83 and 1.85 after a time lapse of 10 days. The dynamics of formation of these structures are modeled through spin-exchange kinetics in the nonequilibrium steady state regime in order to understand their complex behavior. Kawasaki spin exchange dynamics has been applied to a diffusion limited aggregation type fractal object, and the growth of the domains was observed by minimizing the free energy. The fractal dimension of such a system changed from 1.70 to 1.82 which inferred the loss of fractal behavior and the generation of a more compact object. The experimentally observed temporal evolution of these complex structures could be adequately described through the results obtained from the computer simulation data.

Self-organization processes and sedimentation stability in detonation nanodiamond suspensions

Problems related to the stabilization of suspensions prepared from a dry detonation nanodiamond (DND) powder have been studied. Secondary DND suspensions have been obtained and factors influencing their stability with respect to sedimentation have been analyzed. It is shown that the self-organization of particles in DND suspensions in combination with their periodic ultrasonic treatment can be used to convert the maximum possible mass fraction of DND particles in secondary suspensions into nanodimensional (5–100 nm) forms.

Molecular Ordering in Self-Organized Dye Particles

Self-organized rhodamine 6 G particles prepared by wetting/dewetting process of an ethanol solution on a hydophilic glass surface did show fluorescence without quenching. Polarized evanescent field excitation showed that the molecule's transition moment within dye particles was oriented unidirectionally and parallel to the substrate surface. The deduced dye orientation showed correlation between adjacent particles, which implies a simultaneous aggregate growth from a common crystal seed grown in a possible “arm” region connecting the adjacent droplets just before these droplets were disconnected upon solvent evaporation. The dye orientation of most particles pointed about 45° off the dewetting direction. In contrast, the particles of another π-conjugated NK1420 dye, J-aggreagates of which grows easily from an oversaturated solution, showed dye orientation along the dewetting direction preferably, still indicating the effect of self-organization, however based on a different mechanism.

Spectral method study of domain coarsening

The self-organization of particles in a two phase system in the coexistence region through a diffusive mechanism is known as Ostwald ripening. The late stage of Ostwald ripening is studied here through the use of a mesoscopic model in conjunction with a special configuration that allows for the direct measurement of system characteristics such as domain size. The mesoscopic model is a stochastic partial integrodifferential equation and is studied through the use of recently developed and benchmarked spectral schemes. The size of the growing region is not observed to increase as a power law in this model during the late stages of self-organization in contrast to the power law growth observed in simulations of the earlier stages of self-organization. The results included here also demonstrate the effect of adjusting the interparticle interaction on the morphological evolution of the system.

Optimization of system reliability using chaos-embedded self-organizing hierarchical particle swarm optimization

This paper addresses a reliability optimization problem, where the motive is to select the best components for series and series-parallel systems such that system reliability becomes maximized while simultaneously minimizing the cost, weight, and volume. Previous formulation of the problem has implicit restrictions, i.e. it either maximizes system reliability or minimizes the cost. Thus, in order to give a realistic view to the model, a comprehensive objective function has been formulated by combining the normalized values of reliability, cost, weight, and volume. In this paper, a chaos-embedded hierarchical particle swarm optimization (CE-HPSO) algorithm has been proposed to solve the problems arising in the optimization of system reliability using redundancy. The salient features of the proposed algorithm are the use of chaotic sequences and time-varying acceleration coefficients which are responsible for diversifying the search space. Moreover, to restrict the premature convergence, a hierarchical particle swarm optimizer has been used in the proposed algorithm. The performance of the CE-HPSO algorithm has been tested on three benchmark problems and the comparisons are made with genetic algorithm results. In order to check the scalability of the proposed solution methodology, small and large problems are also considered. The results demonstrate the benefits of the proposed algorithm for solving this type of problem.

Near-Field and Polarized Evanescent Field Excited Fluorescence of Self-Organized Particle Arrays of Organic Dye

A wetting/dewetting process was utilized to prepare self-organized organic dye particles of micrometer and submicrometer size. Near-field scanning optical microscopy successfully identified near-field excited near-field fluorescence from single particles. The majority of the small particles with diameters around 2 mm or less, however, did not show fluorescence under near-field observation. In contrast, far-field fluorescence, when excited by a polarized evanescent field, was observed, with the intensity depending on the excitation polarization, indicating that molecules' transition moment within dye particles was oriented parallel to the substrate surface. Single particle fluorescence spectrum consistently showed an identical sharp peak with a large redshift, indicating that the particles were composed of identical dye aggregates similar to J-aggregates. These observations suggest that the near-field at the probe tip was polarized parallel to the probe axis. Another observation, that molecules were oriented in a similar direction among adjacent particles, suggests that the dewetting process contributed to the alignment of the molecular direction among adjacent particles, which further proves that the present specimen was formed by a self-organizing mechanism.

Mesoscopic simulation of Ostwald ripening

The self-organization of particles in a two phase system in the coexistence region through a diffusive mechanism is known as Ostwald ripening. This phenomenon is an example of a multiscale problem in that the microscopic level interaction of the particles can greatly impact the macroscale or observable morphology of the system. Ostwald ripening is studied here through the use of a mesoscopic model which is a stochastic partial integrodifferential equation that is derived from a spin exchange Ising model. This model is studied through the use of recently developed and benchmarked spectral schemes for the simulation of solutions to stochastic partial differential equations. The typical cluster size is observed to grow like t 1 3 over range of times with faster growth at later times. The results included here also demonstrate the effect of adjusting the interparticle interaction on the morphological evolution of the system at the macroscopic level.

Fabrication of luminescent polymeric nanoparticles doped with a lanthanide complex by self-organization process

Recently, a simple method for preparation of polymeric particles with narrow size distribution, “self-organized particle precipitation method”, has been developed. This method is composed of two steps: firstly a solution of a matrix polymer in a volatile solvent is gradually diluted with a freely miscible poor solvent; then the volatile solvent is gradually evaporated from the mixture. In this work, we report preparation of luminescent polystyrene nanoparticles with narrow size distribution from THF solution of polystyrene and trivalent europium, terbium, and samarium complexes as lumophores. Compared with the polystyrene nanoparticles doped with a lanthanide complex possessing no phenyl group, the polystyrene nanoparticles doped with a complex possessing phenyl groups were highly and uniformly luminescent under ultraviolet light irradiation.

Analysis of Molecular Orientation within Self-Organized Dye Particles with Near-Field and Polarized Evanescent-Field Excited Fluorescence

Typical one- or two-dimensional registration was observed in organic dye particles of micrometer and submicrometer size that were formed as precipitates on an ozone-treated hydrophilic glass surface when the organic solvent evaporated from a thin film of specimen solution at a precisely controlled evaporation rate. We successfully identified near-field-excited near-field fluorescence from single particles within these self-organized particle arrays. However, some of the particles, especially most of the small particles with diameters around 2 µm or less, did not show fluorescence under near-field observation. In contrast, far-field fluorescence, when excited by a polarized evanescent field, was observed, with its intensity depending on the excitation polarization, indicating that molecules' transition moment within dye particles orient parallel to the substrate surface. These two observations suggest that the near-field at the tip of the probe was polarized parallel to the probe axis. Another observation, that molecules seemed to orient in a similar direction among neighboring particles, suggests that the dewetting process contributed to the alignment of the molecular direction among adjacent particles, which further proves that the present specimen was formed by a self-organizing mechanism.

Collective-movement teams for cooperative problem solving

Self-organizing particle systems ("swarms") consist of numerous autonomous, reflexive agents ("particles") whose collective movements through space are determined primarily by local influences. Suc...