Self-assembly of latex particles for colloidal crystals

Self-assembly of latex particles is of great importance for fabricating various functional colloidal crystals. In this paper, we review recent research on the self-assembly of latex particles for colloidal crystals, covering the assembly forces and various assembly approaches of latex particles, including self-assembly by gravity sedimentation, vertical deposition, physical confinement, electric field, and magnetic field. Furthermore, some simple methods for assembling latex particles such as spin coating, spray coating, and printing are also summarized.     

A theoretical research to effective viscosity of colloidal dispersions

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悬浮体力学——流体力学与胶体科学交叉的新兴学科

本文介绍了交叉新兴学科悬浮体力学的概貌.该学科发生发展在低Re数流体力学与胶体科学的交叉边缘处.它具有很广泛的应用价值,也有许多吸引人的重要理论课题.近年来在这领域中的研究工作规模十分巨大.对这学科有兴趣的人们而言,这是十分令人鼓舞的时期.在给出了本学科的基本特征和主要研究内容之后,对于相互作用着的低Re数、低Stk数、高Kn数悬浮粒子的运动学,对于在均匀悬浮体中的相对布朗扩散,对于非均匀单分散与多分散悬浮体中的绝对布朗扩散,对于稀释单分散和多分散悬浮体中的重力沉降,对于悬浮粒子的布朗碰并、重力碰并和纯变形场碰并,以及对于高Pcclet数与低Pcclet数下的悬浮体的有效粘性等问题,本文都作了简要的论述.     

老化反应对高碱度烷基水杨酸钙胶体结构及抗磨性的影响

采用冷冻蚀刻电镜（ＦＥ－ＥＭ）,傅立叶红外光谱（ＦＴ－ＩＲ）及钙分布测定等研究了高碱度烷基水杨酸钙的老化过程,并探讨了老化机理,老化反应高碱度烷基水杨酸钙胶体粒子变小,胶体中氢氧化钙的相对含量增加,粘度降低,总碱值（ＴＢＮ）升高;老化后样品的清净性及抗磨性明显提高;水、甲醇及氢氧化钙等影响老化效果。     

COULOMB BLOCKADE EFFECT INSELF-ASSEMBLED GOLD QUANTUM DOTS

Nanometer-scale Au quantum dots have been assembled on SiO2 by controlling the reaction of raw matedais to form a citrate Au sol and an aminosilane/dithiol-treated patterned Si wafer. The detailed formation mechanism has been studied. Three gold colloidal particles (-15 nm), aligned in a chain to form a one-dimensional current path, was bridged across an 80-nm gap between source and drain metal electrodes, The device exhibited a Coulomb blockade effect at 33 K.     

转动驱动圆角立方体颗粒有序堆积的离散元模拟

宏观颗粒体系的有序堆积研究可以为热系统中微观粒子的自组装提供研究模型,也有助于工业生产中提高颗粒材料的填充率.实验发现圆筒中的圆角立方体颗粒受容器往复旋转剪切作用会实现有序堆积.为探究旋转圆筒中立方体颗粒有序堆积过程的内部结构演化过程和动力学机理,采用超二次曲面方程构造了圆角立方体颗粒,基于离散元方法对旋转剪切作用下圆...     

LBM Simulation of Self-Assembly of Clogging Structures by Evaporation of Colloidal Suspension in 2D Porous Media

Transport in Porous Media - Evaporation of colloidal suspension in two-dimensional (2D) porous media leads to the formation of self-assembled clogging structures (SCS). The self-assembly pattern is...     

Flowing colloidal suspensions in non-Newtonian suspending fluids: Decoupling the composite birefringence

The rheology of dilute, colloidal suspensions in polymeric suspending fluids can be studied with simultaneous dichroism and birefringence measurements. The dichroism provides a direct measure of the particle dynamics, but the birefringence is a composite property with independent contributions from the suspended particles and the polymer molecules. For suspensions where the contribution from the particles is significant, the composite birefringence must be decoupled in order to analyze the dynamics of the polymeric suspending fluid. A method to perform the decoupling is derived and then demonstrated through transient shear flow experiments with dilute suspensions ofFeOOH particles in semi-dilute, xanthan gum suspending fluids. The birefringence of the xanthan gum suspending fluid is calculated from experimental measurements of the composite birefringence and the dichroism of the suspension. To gather information on particle/polymer interactions, the calculated birefringence is compared to the birefringence of xanthan gum solutions containing no suspended particles and the dirchoism is compared to that of a suspension in a Newtonian fluid.     

A review on wall slip in high solid dispersions

High solid dispersions are soft materials made of colloidal or non-colloidal particles dispersed at high volume fractions in a liquid matrix. They include hard sphere glasses, colloidal pastes, concentrated emulsions, foams, and vesicles. These materials are prone to exhibit different kinds of flow heterogeneities: shear banding, wall slip, and fracture. While wall slip is often considered as a nuisance by experimentalists, it appears to be a fundamental component to the way that high solid dispersions respond to mechanical deformation. Moreover, the ability of soft materials to slip onto surfaces allows them to move readily and efficiently in many natural phenomena and industrial processes. This review surveys recent developments and current research in the field. Topics like wall slip detection and control, microscopic modeling for rigid and soft particles materials, and the relation between wall slip and other flow heterogeneities are discussed. We also identify important open issues for future research.     

钛基片的化学机械抛光技术研究

采用化学机械抛光（CMP）方法对钛基片进行纳米级平坦化处理,通过系列抛光试验优化抛光液组成和抛光工艺条件后,得到AFM-Ra为0.159 nm的纳米级抛光表面和156.5 nm/min的抛光速率。抛光液的电化学分析结果表明：二氧化硅颗粒和乳酸在钛表面有不同程度的吸附缓蚀作用,氨水和F-的络合、扩散作用能破坏缓蚀膜层,两者的中间平衡状态才能得到最佳抛光效果。抛光后钛表层XPS测试结果显示钛表层经过化学氧化形成疏松氧化层后,再通过磨粒和抛光垫的机械作用去除。     

Bio-inspired short peptide self-assembly: From particles to functional materials

Natural systems are typically featured with tremendous molecular complexity and construct exquisite architectures and functional materials through precise spatial and temporal control. Supramolecular self-assembly from peptides and proteins is believed to be the key player. Thus, knowledge of the fundamental mechanisms driving peptides into vast functional hierarchical structures will certainly help the rational control of self-assembly process, leading to more precise structural organization and functional optimization. In this review, we briefly summarize the recent progress of this burgeoning field mainly from two directions: peptide-based self-assembly and co-assembly with other functional molecules, each part is further divided into two subparts and representative examples are given for each subpart according to their development timeline. At the end of each part, brief summaries of the closely related applications are outlined. For the closing remarks, we conclude with our own understanding of the area and perspectives are given based on recent developments. Overall, this review could be suitable for both new readers to gain a comprehensive overview of the area and experienced readers to get a summary of the development in short peptide self-assembly from particles to functional materials.     

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.     

Microstructure of shear-thickening concentrated suspensions determined by flow-USANS

Reversible shear thickening in colloidal suspensions is a consequence of the formation of hydroclusters due to the dominance of short-ranged lubrication hydrodynamic interactions at relatively high shear rates. Here, we develop and demonstrate a new method of flow-ultra small angle neutron scattering to probe the colloidal microstructure under steady flow conditions on length scales suitable to characterize the formation of hydroclusters. Results are presented for a model near hard-sphere colloidal suspension of 260 nm radius (10% polydisperse) sterically stabilized silica particles in poly(ethylene glycol) at shear rates in the shear thinning and shear thickening regime for dilute, moderately concentrated, and concentrated (ordered) suspensions. Hydrocluster formation is observed as correlated, broadly distributed density fluctuations in the suspension with a characteristic length scale of a few particle diameters. An order–disorder transition is observed to be coincident with shear thickening for the most concentrated sample, but the shear-thickened state shows hydrocluster formation. These structural observations are correlated to the behavior of the shear viscosity and discussed within the framework of theory, simulation, and prior experiments.     

Numerical investigation of particle lateral migration in straight channel flows using a direct-forcing immersed boundary method

Inertia-induced cross-stream migration has been recently exploited for precise position of particles in confined channel flows. In this work, a three-dimensional finite volume based immersed boundary method has been developed to study the lateral migration and hydrodynamic self-assembly of neutrally-buoyant particles in pressure-driven flows. Simulation results show that, in 2D channel flows, the equilibrium position for a circular particle is closer to the centreline for larger particle Reynolds number due to the increasing flow rate, while in 3D square duct flow, the equilibrium position for a spherical particle is near a face centre and is closer to the wall for larger particle Reynolds number. Self-assembly of a pair of particles is observed in 3D square duct flows but not in 2D channel flows. Mechanisms for the self-assembly are discussed.     

Bimodal model of slurry viscosity with application to coal-slurries. Part 1. Theory and experiment

The rheological behavior of stable slurries is shown to be characterized by a bimodal model that represents a slurry as made up of a coarse fraction and a colloidal size fine fraction. According to the model, the two fractions behave independently of each other, and the non-Newtonian behavior of the viscosity is solely caused by the colloidal fraction, while the coarse fraction increases the viscosity level through hydrodynamic interactions. Data from experiments run with colloidal coal particles of about 2–3 µm average size dispersed in water show the viscosity of these colloidal suspensions to exhibit a highly shearrate-dependent behavior and, in the high shear limit, to match very closely the viscosity of suspensions of uniform size rigid spheres although the coal volume fraction must be determined semi-empirically. Different amounts of coarse coal particles are added to the colloidal suspension and the viscosity of the truly bimodal slurries measured as a function of shear rate. In agreement with the bimodal model, the measured shear viscosities show the coarse fraction to behave independently of the colloidal fraction and its contribution to the viscosity rise to be independent of the shear rate. It is shown that the shear rate exerted on the colloidal fraction is higher than that applied by the viscometer as a result of hydrodynamic interactions between the coarse particles, and that it is this effective higher shear rate which is necessary to apply in the correlations. For determining the coal volume fraction a relatively simple and quite accurate measurement technique is developed for determining the density and void fraction of coarse porous particles; the technique directly relates volume fraction to mass fraction.     

Pickering emulsions stabilized by biocompatible particles: A review of preparation,bioapplication, and perspective

The phenomenon of adsorption of solid particles at fluid interfaces to stabilize emulsions or foams have been known for more than a century. Today, particle-stabilized emulsions, often referred to as Pickering emulsions, are receiving growing attention as they are encountered in oil recovery and have long been used in personal care products and food industry. Over the past 10 years the focus of the Pickering emulsion has also increasingly shifted to biomedical applications with thanks to novel syntheses of a wide range of biocompatible particle stabilizers. Here, a brief overview of the development of biocompatible particles is given for Pickering emulsion stabilization, including alginate, poly(lactic-co-glycolic acid) (PLGA), and protein-based particles. The materials prepared by templating from emulsion stabilized with biocompatible particles include colloidal capsules and hierarchically porous materials. It is hoped that the understanding gained from the recent intense activity in the field will enable more researchers to modify existing materials and design new formulations, which would be beneficial for exploring more biological applications.     

Wetting and Prewetting of Anti-Phase Boundaries

A degenerate Allen-Cahn/Cahn-Hilliard system which was developed to describe simultaneous ordering and phase separation, can also be viewed as a diffuse interface approximation for various problems in materials science in which surface diffusion and motion by mean curvature are coupled. In the original context a low temperature coarsening limit, yielding geometric motion in the limit, was designed to describe small particles of a disordered phase whose shape evolves by surface diffusion which are embedded along grain boundaries which partition the system into two ordered variants. While an early analysis focused on systems in the proximity of the complete wetting limit [9], a later analysis extended these results also to the partial wetting setting [11]. We outline here some features which determine whether a given degenerate Allen-Cahn/Cahn-Hilliard system corresponds to complete or partial wetting in the limit, giving some explicit examples of both possibilities.     

The “Inverse Hall-Petch” effect on the impact response of single crystal copper

Based on the available experimental and computational capabilities, a phenomenological approach has been proposed to formulate a hypersurface in both spatial and temporal domains to predict combined specimen size and loading rate effects on the material properties [1-2]. A systematic investigation is being performed to understand the combined size, rate and thermal effects on the properties and deformation patterns of representative materials with different nanostructures and under various types of loading conditions [3- 16]. The recent study on the single crystal copper response to impact loading has revealed the size-dependence of the Hugoniot curve. In this paper, the "inverse Hall-Petch" behavior as observed in the impact response of single crystal copper, which has not been reported in the open literature, is investigated by performing molecular dynamics simulations of the response of copper nanobeam targets subjected to impacts by copper nanobeam flyers with different impact velocities. It appears from the preliminary results that the "inverse Hall-Petch" behavior in single crystal copper is mainly due to the formation and evolution of disordered atoms and the interaction between ordered and disordered atoms, as compared with the physics behind the "inverse Hall-Petch"behavior as observed in nanocrystalline materials.     

基于粗粒化分子动力学的自由水与水化硅酸钙孔隙水冻结模拟

水化硅酸钙是水泥基材料的主要水化产物,其孔隙内的水分是影响水泥基材料抗冻性的主要因素。本文基于粗粒化分子动力学方法研究水化硅酸钙孔隙水的冻结机制,针对水的粗粒化P₄粒子和水化硅酸钙胶体颗粒,建立了水化硅酸钙孔隙水的冻结模型。根据此模型计算了不同孔径孔隙水冰点,分析了水泥基材料孔径孔隙在冻融破坏中的危害程度;模拟得到了水化硅酸钙孔隙内水的冻结分布特征和密度分布特征。研究工作表明,本文建立的模型有效提高了分子动力学模拟水化硅酸钙孔隙水冻结问题的规模,为后续进行水泥基材料的冻融破坏分析提供了研究基础。     

胶体自组装过程中的形核与绕流影响

应用长工作距显微镜对胶体粒子自组装过程中初形核阶段进行了原位观察实验研究, 并结合 三相接触线附近流场的数值模拟结果对绕流的影响进行了研究. 研究表明流线在短链附近发 生弯曲. 当颗粒靠近短链附近时, 水平流将颗粒推向短链的端部. 绕流将抑制形核过程中局 部的过快生长, 从而保持生长前沿平直.