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Particle Assemblies (particle + assembly)

Distribution by Scientific Domains

Polymers and Materials Science	90%

Selected Abstracts

Influence of inherent anisotropy on mechanical behavior of granular materials based on DEM simulations

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2010
Zafar Mahmood
Abstract We study the influence of inherent anisotropy, i.e. bedding angle on stress,strain behavior and shear band formation in quasi-static granular media. Plane strain biaxial tests are carried out using two-dimensional distinct element method (DEM). Oval/elliptical-shaped particles are generated by overlapping the discrete circular elements. Particle assemblies with four different bedding angles are tested. Evolution of the microstructure inside and outside the shear band and effect of bedding angle on the microstructure are investigated. Influence of bedding angle on fabric and force anisotropy is studied. It is found that by using non-circular particles, generation of large voids and excess particle rotations inside the shear band are reproduced in a quite similar manner to those of the natural granular soils, which are difficult to produce with standard DEM simulations using circular particles. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Silver Nanoparticles with Controlled Dispersity and Their Assembly into Superstructures

ADVANCED ENGINEERING MATERIALS, Issue 5 2010
Karsten Moh
In this paper we report on the influence of particle size distribution, particle substrate interaction, and drying behavior on the self-assembly process using ligand stabilized silver particles. Two-dimensional particle arrays were characterized using transmission electron microscopy and extensive image analysis. The formation of such structures was observed in situ using an environmental scanning electron microscope in WET-STEM mode. The results confirm that a small particle size distribution is crucial for the formation of regular particle patterns with long range order, but also the particle substrate interaction and the particle density have an influence on the degree of ordering. Additionally, we find that separated binary particle assemblies keep the orientation of their two-dimensional hexagonal lattices over alternating domains of small and big particles. This is probably enabled due to the formation of dislocations and a small change of the course of the lattice lines within the respective boundary. [source]

Particle-Stabilized Materials: Particle-Stabilized Materials: Dry Oils and (Polymerized) Non-Aqueous Foams (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
Mater.
On page 732, Dr. R. Murakami and Professor A. Bismarck describe the synthesis of three different materials systems based on the mechanism of adsorption of colloidal particles at air,oil surfaces. Their inside cover images shows squalane drops stabilized against coalescense by assemblies of tetrafluoroethylene oligomer particles. These particle assemblies result in the formation of a metastable Cassie,Baxter wetting state, causing the oil drops to change in behavior from wet particles to dry free-flowing materials. [source]

Particle-Stabilized Materials: Dry Oils and (Polymerized) Non-Aqueous Foams

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2010
Ryo Murakami
Abstract Oil (liquids with low surface tension and practically immiscible with water) drops can be dispersed in air if relatively oleophobic particles are available. However, such particles with oil-repellent surfaces cannot simply be prepared by controlling the particle surface chemistry alone. Herein the preparation of oil-in-air materials (oil marbles, dry oils) by changing the wetting behavior of particles by tuning the oil properties, which allows the formation of the metastable Cassie,Baxter wetting state of particle assemblies on oil drop surfaces, is presented. The oil-in-air materials can be converted to air-in-oil materials (non-aqueous foams) by tailoring the oil properties, as the robustness of the metastable Cassie,Baxter state of the particle assemblies critically depends on the particle wettability. This conversion implies the phase inversion of dispersed systems consisting of air and oils. It is also shown that particle-stabilized non-aqueous foams can be utilized as template to produce macroporous polymers. [source]

Materials Fabricated by Micro- and Nanoparticle Assembly , The Challenging Path from Science to Engineering

ADVANCED MATERIALS, Issue 19 2009
Orlin D. Velev
Abstract We classify the strategies for colloidal assembly and review the diverse potential applications of micro- and nanoparticle structures in materials and device prototypes. The useful properties of the particle assemblies, such as high surface-to-volume ratio, periodicity at mesoscale, large packing density, and long-range ordering, can be harnessed in optical, electronic, and biosensing devices. We discuss the present and future trends in the colloidal- assembly field, focusing on the challenges of developing fabrication procedures that are rapid and efficiently controlled. We speculate on how the issues of scalability, control, and precision could be addressed, and how the functionality of the assemblies can be increased to better match the needs of technology. [source]

Cover Picture: Closing the Gap Between Self-Assembly and Microsystems Using Self-Assembly, Transfer, and Integration of Particles (Adv. Mater.

ADVANCED MATERIALS, Issue 20 2005
20/2005)
Abstract The cover shows 100 ,,m diameter glass spheres covered by a grid of hexagonally packed polystyrene beads. Wolf and co-workers placed the 500,nm diameter polystyrene beads onto the larger spheres using the self-assembly, transfer, and integration (SATI) process that they report on p.,2438. The cover illustrates the capability of SATI to process uneven surfaces in addition to the planar substrates discussed in the article. The carrier that holds the smaller beads deforms during their transfer onto the larger spheres, so that on the larger spheres patterned "caps" are formed. Using this process, which is compatible with standard microfabrication techniques, a variety of particle assemblies can be achieved. [source]

Anisotropic Particle Synthesis Inside Droplet Templates on Superhydrophobic Surfaces

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 2 2010
Vinayak Rastogi
Abstract We demonstrate how droplet templates dispensed on superhydrophobic substrates can be used to fabricate both shape-anisotropic ("doughnut") and composition-anisotropic ("patchy magnetic") supraparticles. The macroscopic shape of the closely-packed particle assemblies is guided by the droplet meniscus. Aqueous droplets of monodisperse microsphere suspensions dispensed on the substrates initially acquire near-spherical shape due to a high contact angle. During the solvent evaporation, however, silica suspension droplets undergo shape transitions (concaving) guiding the structure of the final assemblies into doughnut supraparticles. Composition anisotropy is achieved by drying a droplet containing a mixed suspension of latex and magnetic nanoparticles, while exposing it to magnetic field gradients. Depending on the pattern of the magnetic fields, the magnetic nanoparticles segregate into single, bilateral, or trilateral, patched spherical supraparticles. The physical effects leading to the development of anisotropy are discussed. Unlike the conventional wet self-assembly (WSA) methods where the final structures need to be extracted from the liquid environment, this efficient one-step procedure produces ready to use "dry" supraparticles. [source]

The Synthesis and Assembly of Polymeric Microparticles Using Microfluidics

ADVANCED MATERIALS, Issue 41 2009
Dhananjay Dendukuri
Abstract The controlled synthesis of micrometer-sized polymeric particles bearing features such as nonspherical shapes and spatially segregated chemical properties is becoming increasingly important. Such particles can enable fundamental studies on self-assembly and suspension rheology, as well as be used in applications ranging from medical diagnostics to photonic devices. Microfluidics has recently emerged as a very promising route to the synthesis of such polymeric particles, providing fine control over particle shape, size, chemical anisotropy, porosity, and core/shell structure. This progress report summarizes microfluidic approaches to particle synthesis using both droplet- and flow-lithography-based methods, as well as particle assembly in microfluidic devices. The particles formed are classified according to their morphology, chemical anisotropy, and internal structure, and relevant examples are provided to illustrate each of these approaches. Emerging applications of the complex particles formed using these techniques and the outlook for such processes are discussed. [source]

Synthesis and Assembly of Monodisperse High-Coercivity Silica-Capped FePt Nanomagnets of Tunable Size, Composition, and Thermal Stability from Microemulsions,

ADVANCED MATERIALS, Issue 19 2006
Q. Yan
A microemulsion approach to obtain high - coercivity (850 mT) FePt nanomagnets capped with a nanoscopic silica shell is reported (see figure). This versatile method allows the easy tuning of particle size and composition. The silica shell inhibits agglomeration and preserves the chemical stability of the particles up to 650,°C, and facilitates surface functionalization and particle assembly. These attributes are attractive for harnessing the nanomagnets for realizing novel devices and composites. [source]

Production of Ceramic Green Bodies Using a Microwave-Reactive Organic Binder

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2007
Kimiyasu Sato
Because the pyrolysis of organic substances can result in the emission of harmful pollutant gases, a reduction in the use of organic binders is one aim of today's ceramics industry. A novel ceramic-forming process was developed that requires considerably less organic binder than conventional techniques. The process involves immobilizing reactive molecules on the surfaces of the particles, which on subsequent irradiation with microwaves, form bridges that bind the entire particle assembly together. The chemical forces involved produce strong bonds, resulting in a significant reduction in the amount of organic binder that is required to maintain the shape of the ceramic green body. This method will help to decrease emissions of harmful gases produced from pyrolysis of the binder. [source]