Facile Fabrication of Anisotropic Colloidal Particles with Controlled Shapes and Shape Dependence of Their Elastic Properties

A facile technique with only one step for fabrication of anisotropic colloidal particles at the air/water interface is demonstrated. Anisotropic colloidal particles with controlled shapes can be easily obtained by tuning the incubation time in solvent vapor at room temperature. The formation of separate anisotropic particles is attributed to the lateral stretch on the particles by the interfacial forces and repulsion among the neighboring particles by the generation of the polymer solution flows. To further explain the proposed formation mechanism of the colloidal particles with shape anisotropy, an in situ experiment is designed for direct observation of the arrangement change of the colloidal particles. This fabrication technique is general and applicable to polymer colloidal particles with various initial sizes ranging from microscale to nanoscale. Moreover, the elastic properties of the anisotropic colloidal particles are measured which exhibit a prominent change with different shapes and the change trend of the elastic moduli is similar for particles with different original sizes. This work provides a versatile approach for fabrication of anisotropic colloidal particles with tunable shapes and sizes and establishes the interplay between particle shape and elastic property, which is much valuable for further research on the effect of particle parameters on drug delivery process.     

Electrostatic charging of micro- and nano-particles for use with highly energetic applications

Electrostatically charging spherical and cylindrical conducting particles against an electrode with an applied electric field is investigated both theoretically and experimentally as a method of charging micro- and nano-particles for use with a variety of high energy and high velocity applications, which include nano-particle electrostatic space propulsion systems, materials processing, and nano-printing. Increasing the particles' charge-to-mass ratios is critical for maximizing their velocities when accelerated with applied electric fields, which requires minimizing the particles' sizes down to the micro- and nano-meter ranges for some applications. An analysis reveals that the charge-to-mass ratio is maximized with low aspect ratio particles when the maximum electric field strength, which is at the top of the particles, is held constant. Experimental results of charging titanium and aluminum spherical and cylindrical particles are presented, which suggest that under appropriate conditions, the particles are charged as predicted by theory. But that electrical contact resistance between the particles and electrode can influence the charging time. An analysis of the expected particle charging times is presented, which shows a strong dependence on the conductivity and thickness of the oxide layer coating the particles.     

Generalized Locking Profile for Angular Particles - Locked Particle Theory

Locked particles are defined as those comminuted or particles which contain both gangue and target material. By considering the shape of the comminuted particles and assuming their random distribution in the ore body prior to comminution, it is possible to derive locking profiles which give the frequency of occurrence of particles which have a given fraction of their volume occupied by target material. For most particle shapes (spheres, angular particles, angular plates and rods) the locking profile is a deep U-shaped curve. This suggests that few particles by number contain about 50% target material while a far greater number contain either very little or very much target material. Such a conclusion is important in planning separation processes for locked particles in the mineral industry.     

分散相颗粒几何因素对电流变液体反应时间的影响

瞬变的反应时间是电流变液体的一个重要参数．本文通过实验和理论分析，建立了考虑分散相颗粒几何因素的电流变反应时间模型根据此模型，长椭球状颗粒的电流变液体反应时间比等效球状颗粒的短，扁椭球状和片状颗粒的电流变液体反应时间比等效球状颗粒的长，而棒状颗粒的电流变液体反应时间则视ε_p/ε_f比值大小或快于或慢于等效球状颗粒的反应时间．且反应时间与分散相尺寸的关系是（１）随体积增大，各种形状颗粒的电流变液体反应时间均变短；（２）同体积下，随长径比增大，长椭球状颗粒的电流变液体反应时间变短，而扁椭球状颗粒和片状颗粒的电流变液体反应时间变长，棒状颗粒的电流变液体反应时间则视。ε_p/ε_f比值大小或增快或减慢．因此，要获得反应快的电流变液体，颗粒形状除选择球状外，还可在使雷诺数较小范围内，选择一定尺寸的长椭球状或棒状颗粒。 关键词：     

New micromagnetic states of magnetically soft nanoparticles with a nearly cubic shape

The ground state of nonellipsoidal particles can be inhomogeneous due to the effect of a demagnetizing field. The approach proposed here for studying such particles is based on the combination of symmetry analysis and perturbation theory. The general formulation of this approach, which makes it possible to analyze weakly inhomogeneous states for particles with a complex shape, is considered. The ground state of cubic particles of magnetically soft materials is calculated analytically, and the effect of small strains of cubic particles on the magnetization distribution in the particles is investigated. It is shown for the example of magnetically soft cubic particles that even a small deviation of the particle shape from symmetrical may result in the realization of a special magnetic state in such particles, in which the symmetry in the magnetization distribution is lower than the particle symmetry. A change in the parameters of a particle can substantially modify its magnetic properties and may even induce a phase transition to a state with a different symmetry.     

随机分布粒子侧向散射光特性的实验研究

两种不同直径(0．22μm和0．494μm)的粒子与过滤的蒸馏水制作不同体积分数的悬浮液作为散射介质。比较了微粒子群侧向散射光中垂直与水平两种偏振光的强度分布。实验结果表明，直径大的粒子其侧向散射光中水平方向线偏振强度远远小于直径小的粒子，而垂直方向线偏振强度却完全相反，远远大于直径小的粒子。     

Effective transport of passive particles induced by chiral-active particles in microchannel

Transport of passive particles induced by chiral-active particles in microchannel is investigated by using the overdamped Langevin dynamics simulation in a two-dimensional model system. Due to the chirality of active particles and special structure of microchannel, effective ratchet transport of passive particles is achieved. Effective transport of passive particles depends on the width of microchannel(d), the density(ρ), and the angular velocity(ω) of chiral-active particles.There exist optimal parameters for d and ω at which the transport efficiency for passive particles takes its maximal value.This investigation can help us understand the necessity of active motion for living systems to maintain a number of vital processes such as materials transport inside cells and the foraging dynamics of mobile organisms.     

Fock Theories and Quantum Logics

The notion of Fock theory is introduced in the framework of quantum logics, which are here orthomodular atomic lattices satisfying the covering property. It is shown that there are some fundamental facts concerning particles, which may be successfully discussed in this general context. One of these facts is to establish the theoretical conditions for considering particles as sharply defined entities. The other refers to the theoretical circumstances, which almost impose to consider that some particles have a structure, meaning they are composed from other particles. This last problem is strongly related with the conservative time evolutions.     

On the theoretical problems in constructing interactions involving higher-spin massless particles

It is shown that a gauge theory of self-interacting massless spin-3 particles which is analogous to Yang-Mills or the theory of gravity does not exist. A way out may be the existence of an interacting infinite family of massless particles of various spins. The first-order interactions which are possible between such particles show a remarkable structure. This is established by explicit construction. Detailed results are obtained for the possible algebraic structures which one may obtain for gauge theories which are induced from the gauge invariance of free lagrangians.     

Temperature and magnetic field responsive hyaluronic acid particles with tunable physical and chemical properties

We report the preparation and characterization of thiolated-temperature-responsive hyaluronic acid-cysteamine-N-isopropyl acrylamide (HA-CYs-NIPAm) particles and thiolated-magnetic-responsive hyaluronic acid (HA-Fe-CYs) particles. Linear hyaluronic acid (HA) crosslinked with divinyl sulfone as HA particles was prepared using a water-in-oil micro emulsion system which were then oxidized HA-O with NaIO₄ to develop aldehyde groups on the particle surface_. HA-O hydrogel particles were then reacted with cysteamine (CYs) which interacted with aldehydes on the HA surface to form HA particles with cysteamine (HA-CYs) functionality on the surface. HA-CYs particles were further exposed to radical polymerization with NIPAm to obtain temperature responsive HA-CYs-NIPAm hydrogel particles. To acquire magnetic field responsive HA composites, magnetic iron particles were included in HA to form HA-Fe during HA particle preparation. HA-Fe hydrogel particles were also chemically modified. The prepared HA-CYs-NIPAm demonstrated temperature dependent size variations and phase transition temperature. HA-CYs-NIPAm and HA-Fe-CYs particles can be used as drug delivery vehicles. Sulfamethoxazole (SMZ), an antibacterial drug, was used as a model drug for temperature-induced release studies from these particles.     

玻璃-橡胶混合颗粒体系的弹性行为研究

废旧橡胶制品颗粒与砂土颗粒混合物作为建筑填充材料具有环保、轻质、减震效果好等特点.软硬组分的混合比例可以调制体系力学性能从而实现兼顾材料柔韧性与强度的需求,但细观层面上材料性能改变的原因尚不明确.本文主要研究玻璃-橡胶混合颗粒体系的弹性行为及其微观机制.利用飞行时间法测量混合材料等效动弹性模量,发现随着橡胶颗粒增加,体系逐渐从类玻璃刚性行为转变为类橡胶柔性行为.离散元模拟结果与实验结果类似.此外,模拟显示低橡胶颗粒占比样品内主要由玻璃颗粒构成主力链结构,而橡胶颗粒基本不参与强力链的构成.当橡胶颗粒占比较大时,玻璃颗粒和橡胶颗粒共同构成主力链网络结构,但颗粒间法向接触力分布相对更为均匀,可视为玻璃颗粒悬浮于橡胶颗粒中.基于上述结果,提出了改进的等效介质理论,用于描述混合颗粒体系的弹性行为.研究认为:橡胶颗粒占比较小时内部颗粒的变形相对均匀,材料近似满足等应变假设,视为并联弹簧模型;橡胶颗粒占比较大时混合材料近似满足等应力假设,视为串联弹簧模型.两种模型得到的结果与模拟结果一致.上述结果有利于从微观角度揭示混合颗粒材料弹性行为的变化机制.     

Colloidal aggregation in a nematic liquid crystal: topological arrest of particles by a single-stroke disclination line

We numerically study many-body interactions among colloidal particles suspended in a nematic liquid crystal, using a fluid particle dynamics method, which properly incorporates dynamical coupling among particles, nematic orientation, and flow field. Based on simulation results, we propose a new type of interparticle interaction in addition to well-known quadrupolar interaction for particles accompanying Saturn-ring defects. This interaction is mediated by the defect of the nematic phase: upon nematic ordering, a closed disclination loop binds more than two particles to form a sheetlike dynamically arrested structure. The interaction depends upon the topology of a disclination loop binding particles, which is determined by aggregation history.     

The collision of particles in granular systems

Collisions between granular particles are irreversible processes which cause dissipation of mechanical energy by fragmentation or heating of the colliders. The knowledge of these phenomena is essential for the understanding of the behaviour of complex systems of granular particles. We have developed a model for inelastic collisions of granular particles and calculated the velocity restitution coefficients, which describe all possible collisions in the system. The knowledge of these coefficients allows for event-driven many-particle simulations which cannot be performed in the frame of molecular dynamics. This approach has the advantage that very large particle numbers can be treated which are necessary for the understanding of intrinsic large-scale phenomena in granular systems.     

A grid based particle method for moving interface problems

We propose a novel algorithm for modeling interface motions. The interface is represented and is tracked using quasi-uniform meshless particles. These particles are sampled according to an underlying grid such that each particle is associated to a grid point which is in the neighborhood of the interface. The underlying grid provides an Eulerian reference and local sampling rate for particles on the interface. It also renders neighborhood information among the meshless particles for local reconstruction of the interface. The resulting algorithm, which is based on Lagrangian tracking using meshless particles with Eulerian reference grid, can naturally handle/control topological changes. Moreover, adaptive sampling of the interface can be achieved easily through local grid refinement with simple quad/oct-tree data structure. Extensive numerical examples are presented to demonstrate the capability of our new algorithm.     

On the mechanism of own rotation of dust particles

We analyze the physical reason for own rotation of dust particles. We propose from analysis of literature data and our previous studies that own rotation of dust particles is due to azimuth-symmetric flow of ions to the particle surface, which is associated with a nonuniform distribution of the surface charge. This assumption is in conformity with the results of experiments in which the plasma flow is changed by introducing particles in the horizontal plane (horizontal cluster) and particles aligned along the discharge current (vertical cluster) and with the observation of the rotation threshold for the discharge current and the magnetic field. The experiments are performed with spherical particles using the coordinate tracing method. Our results make it possible to construct a model of spinning of charged dust tops for describing magnetic properties of a complex plasma.     

Non-ergodicity of Two Particles Interacting via a Smooth Potential

We examine two point particles interacting via a smooth Lennard-Jones-type potential of finite range on a two-dimensional torus. We find situations under which this system contains a stable, elliptic periodic orbit and hence is not ergodic. This result is in contrast to the case of hard spheres interacting via inelastic collision, which are always ergodic for two particles, are conjectured to be ergodic for arbitrarily many particles, and can never contain elliptic periodic orbits.     

Spatial arrangements of particles with different mobility tendencies in a model glass-former

The use of the isoconfigurational method has enabled one to determine the existence of particles with high and low dynamic propensity (tendency to be mobile) and particles with preferred directionality for motion (directional particles) in supercooled liquids. On the other hand, dynamical studies have shown that the relaxation of such systems evolves by means of rapid crossings between metabasins of the potential energy surface (a metabasin being a group of mutually similar, closely related structures which differ markedly from the ones belonging to other metabasins), as collectively relaxing units (d-clusters) take place. Here we determine the spatial arrangements of such particles in a model three dimensional glass-forming system. We show that both the highest and the lowest propensity particles form compact clusters, which are separated from each other by the high directionality particles. The particles of this interfacial region seem to behave as to help make room for the enhanced (expansion) movement of the high propensity cluster and to keep the local density constant. Finally, we also find that only the high propensity particles (but not the directional ones) exhibit a great tendency to take part in d-cluster events.     

四流体模型与m=1内扭曲模稳定性分析

利用描述俘获粒子运动的四流体模型推导出包含俘获粒子效应,离子反磁漂移,有限电阻及反常电子粘滞效应的ｍ＝１的内扭曲模本征方程和色散关系,并在等离子体芯部存在与不存在的高能粒子的两种情况下,讨论了俘获粒子效应和各种耗散效应对内扭曲模的影响。     

Explosive condensation in a mass transport model

We study a far-from-equilibrium system of interacting particles, hopping between sites of a 1D lattice with a rate which increases with the number of particles at interacting sites. We find that clusters of particles, which initially spontaneously form in the system, begin to move at increasing speed as they gain particles. Ultimately, they produce a moving condensate which comprises a finite fraction of the mass in the system. We show that, in contrast with previously studied models of condensation, the relaxation time to steady state decreases as an inverse power of lnL with system size L and that condensation is instantaneous for L→∞.