Synthesis Of Anisotropic Particles Research Articles

Anisotropic particle synthesis and characterization for lithium-ion battery electrode materials via precursor precipitate growth inhibitor

To achieve higher power and energy density batteries, electrodes are often designed towards increased current densities and thicknesses. Under such conditions, electrode microstructure can become an important factor. Electrode microstructure is dependent on many factors, but one factor that can facilitate anisotropic microstructures is having anisotropic lithium-ion battery active material particles. Thus, robust methods to produce active materials with anisotropic particle morphologies are desirable. This manuscript will describe the use of an inhibitor to direct anisotropic morphologies of lithium-ion battery precursor particles. This anisotropic secondary platelet morphology was retained after conversion to final active material particles. The synthesis method should be generally applicable to producing a variety of transition metal oxide compositions with anisotropic morphologies, however, the inhibitor can have significant impacts on the rate of precipitation of the transition metals during precursor synthesis. Three exemplar materials will be described towards targeted synthesis of anisotropic cathode particles.

Emulsion-Guided Controllable Construction of Anisotropic Particles: Droplet Size Determines Particle Structure.

Anisotropic particles have attracted significant attention due to their alluring features that distinguish them from isotropic particles. One of the most appealing strategies for the synthesis of anisotropic particles is the emulsion-guided method. However, morphological control and the understanding of formation mechanisms have remained a major challenge. Based on a novel mechanism, here, a facile one-pot emulsion-templating method for the tunable construction of anisotropic polymeric particles (APPs) with different defined structures is reported. Three types of monocomponent APPs with new morphologies and sizes in the range of 240-650nm, including Janus mushroom-like mesoporous poly(m-phenylenediamine) (PmPD) particles, wheel-shaped particles, and acorn-like PmPD particles, are obtained by controlling the average size of the oil droplets in the emulsion. Furthermore, the APPs demonstrate the ability for conversion to nitrogen-doped anisotropic carbon particles (ACPs) by pyrolysis at 800°C under a N2 atmosphere, thereby inheriting their structures. These novel ACPs show appreciable potential as metal-free electrocatalysts for use in oxygen reduction reactions. Compared to their isotropic counterpart, these ACPs exhibit remarkable advantages such as enhanced specific surface area and pore volume, reduced stacking density, and easy fabrication of continuous and uniform membrane electrodes.

Interfacial Configurations of Lens-Shaped Particles

We study the configuration behaviors of non-spherical lens-shaped particles at a fluid-fluid interface. The attachment energies of truncated spheres and biconvex particles are calculated numerically to determine the thermodynamically stable configuration of the particles at the interface. When the particle is rotated 180° perpendicular to the interface, two energy minima are observed in the attachment energy profile. One corresponds to equilibrium and the other to a metastable orientation. The high energy barrier between the two energy minima indicates that the particle with the metastable condition is not spontaneously converted to the equilibrium state, such that the interface adsorption and orientation behaviors of the particles are irreversible and are determined stochastically. A further comprehensive investigation of the interfacial pinning phenomena of the truncated or biconvex boundary and free-rotation of the particles is also performed for different wettability and geometric factors. This study offers simple design rules for the synthesis of anisotropic particles used as a solid surfactant.

A Diversity of Asymmetric Nano-/Microcolloidal Architectures Grown by ATRP from Janus Seeds.

The fabrication of colloids has witnessed significant progress during the last decade, however, fabrication of anisotropic colloidal particles with complex geometries still represents a challenging task. Here, we present nano-/micro-sized colloidal architectures which 'grow' directly from nanoparticle seeds by controlled radical polymerization, resembling the growth of plants from seeds in the natural world. Specifically, we use the atom transfer radical polymerization (ATRP) technique to grow colloidal architectures from snowman-shaped Janus nanoparticle seeds (JNPS). The key to this synthetic approach is the asymmetric placement of the ATRP initiators in the bulk of one JNPS lobe. By starting the polymerization, monomers continuously add to the initiator containing the JNPS lobe, which subsequently grows into a larger colloidal structure. By controlling growth conditions mainly through the interaction strength between the monomer and JNPS, a variety of colloidal architectures result, for example, dish-, basket, cocoon-, flower-, helmet- mushroom-, dumpling and pumpkin-like geometries. Furthermore, each of these grown architectures have different surface morphologies, including smooth-, island- and grouped island nanostructures. The present work provides an alternative method to the synthesis of anisotropic particles with complex geometries and tunable surface morphologies, thus enriching the toolbox for the colloid synthesis.

Seedless synthesis and SERS characterization of multi-branched gold nanoflowers using water soluble polymers.

We report for the first time, the aqueous-based synthesis of multibranched, monodispersed gold nanoflowers (AuNFs) using pyromellitic dianhydride-p-phenylene diamine - PPDDs at room temperature. AuNF synthesis was achieved using PPDDs that converts Au precursor (Au3+) into AuNFs while serving as both the reducing and directional agent. The resulting branched AuNFs exhibited different degrees of anisotropy and protuberance lengths obtained by modulating the ratio of PPDDs and HAuCl4·3H2O. The surface roughness obtained ranged from small bud-like protuberances to elongated spikes, which enabled the tuning of the optical properties of the nanoparticles from ∼450 to 1100 nm. Systematic analysis revealed that the generation of urchin-like particles as well as their size depended on the PPDDs/HAuCl4·3H2O ratio. At a medium concentration of the precursor, spherical nanoparticles were formed. Whereas at lower precursor concentrations, urchin-like nanoparticles were obtained with their size and protuberances length increasing at even lower HAuCl4·3H2O concentration. Increasing the temperature to 100 °C resulted in the enhancement of the anisotropy of the AuNFs. The resulting gold nanoflowers exhibited an enhanced performance in surface-enhanced Raman scattering (SERS). This work provides a unique approach for anisotropic particle synthesis using water soluble polymer and greener approaches. The fabricated AuNFs exhibited variable UV-vis absorption and SERS enhancement as a function of branch morphology, indicating their potential application in biolabeling, biosensing, imaging, and therapeutic applications.

Direct one-pot synthesis of chemically anisotropic particles with tunable morphology, dimensions, and surface roughness.

Previously, synthesis of anisotropic particles by seeded polymerizations has involved multiple process steps. In conventional one-pot dispersion polymerization (Dis.P) with a cross-linker added, only spherical particles are produced due to rapid and high cross-linking. In this Article, a straightforward one-pot preparation of monodisperse anisotropic particles with tunable morphology, dimensions, surface roughness, and asymmetrically distributed functional groups is described. With a cross-linker of divinylbenzene (DVB, 8%), ethylene glycol dimethacrylate (EGDMA, 6%), or dimethacryloyloxybenzophenone (DMABP, 5%) added at 40 min, shortly after the end of nucleation stage in Dis.P of styrene (St) in methanol and water (6/4, vol), the swollen growing particles are inhomogeneously cross-linked at first. Then, at low gel contents of 59%, 49%, and 69%, corresponding to the cases using DVB, EGDMA, and DMABP, respectively, the growing particle phase separates and snowman- or dumbbell-like particles are generated. Thermodynamic and kinetic analyses reveal that moderate cross-linking and sufficient swelling of growing particles determine the formation and growth of anisotropic particles during polymerization. Morphology, surface roughness, sizes, and cross-linking degrees of each domain of final particles are tuned continuously by varying start addition time and contents of cross-linkers. The snowman-like particles fabricated with DVB have a gradient cross-linking and asymmetrical distribution of pendant vinyl groups from their body to head. The dumbbell-like particles prepared using DMABP have only one domain cross-linked; i.e., only one domain contains photosensitive benzophenone (BP) groups. With addition of glycidyl methacrylate (GMA) or propargyl methacrylate (PMA) together with DVB or EGDMA, epoxy or alkynyl groups are asymmetrically incorporated. With the aid of these functional groups, carboxyl, amino, or thiol groups and PEG (200) are attached by thiol-ene (yne) click and photocoupling reactions.

Facile synthesis of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies for single-particle surface-enhanced Raman scattering.

The physicochemical properties of noble metal nanocrystals depend strongly on their size and shape, and it is becoming clear that the design and facile synthesis of particular nanostructures with tailored shape and size is especially important. Herein a novel class of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies and optical properties are prepared for the first time by a facile, one-pot, seedless synthesis using ascorbic acid (AA) to reduce hydrogen tetrachloroaurate (HAuCl4) in the presence of (1-hexadecyl)trimethylammonium chloride (CTAC). The morphologies of the synthesized gold nanoflowers are controlled and fine-tuned by varying the synthetic conditions such as the concentration of reagents and the growth temperature. Due to their unique hierarchical three-dimensional (3D) structures with rich hot spots, these gold nanoflowers exhibit an efficient performance in single-particle surface-enhanced Raman scattering (SERS). The work stands out as an interesting approach for anisotropic particle synthesis and morphological control, and the proposed novel, hierarchical gold nanoflowers have a number of exciting potential applications in SERS-based sensors.

Facile synthesis of core-shell, multiple compartment anisotropic particles via control of cross-linking and continuous phase separations in one-pot dispersion polymerization

Preparation of anisotropic particles based on phase separation of prefabricated seeds in polymerizations generally involves multiple process steps. In conventional one-pot dispersion polymerization, only spherical particles are produced. Herein, anisotropic particles with asymmetrical core-shell structure, multiple compartments, and continuously tunable surface roughness and sizes were synthesized by a modified one-pot dispersion polymerization. A mixture of polar solvents, ethylene glycol (EG), and water (6/4, vol.) was used as medium for polymerization of styrene (St). In the presence of ammonium persulfate (APS) and vinyl acetate (VA), divinylbenzene (DVB, 16.1–66.4 %) and (St, 50.3–0 %) were added at 60, 180, and 360 min, respectively. Dense cross-linking was confined to exterior of swollen growing particles, resulting in phase separation and formation of snowman-like particles with coarse, core-shell structured body, and smooth, no or partially cross-linked head. The newly formed compartments were also inhomogeneously cross-linked and their phases separated, producing three and four compartment anisotropic particles with an aspect ratio up to 2.3. Gel content of final particles was less than 75 %. Due to a sequential cross-linking from growing particle to newly formed compartments, reaction stability and particle monodispersity were maintained even when high amounts of DVB were added. Asymmetrical morphologies, structures, sizes, and surface roughness of particles were continuously tuned by varying DVB amount and its start addition time. This one-pot method provides a simple, efficient route for synthesis of anisotropic particles.

Nanoplasmonic Modification of the Local Morphology, Shape, and Wetting Properties of Nanoflake Microparticles

Inducing a phase transition of a self-organized object may trigger its structural transformation. Here, we demonstrate local control of the morphology and shape of self-organized microparticles with a nanoflake outer surface by nanoplasmonic heating. To increase the photothermal efficiency of the microparticles, gold nanoparticles (AuNPs) or single-walled carbon nanotubes (SWCNTs) were incorporated. AuNPs and SWCNTs, which have excellent photothermal activity, acts as photoresponsive heat converters. Because they have distinct absorption characteristics, visible or near-infrared lasers can be used to induce local heating. The photothermal effect was used to spatially confine the melting to the space within the particle and the aggregate; as a result, microparticles with various shapes and morphologies have been fabricated. Such morphological changes lead to a superhydrophobic-hydrophobic wetting transition, which was confirmed by the films constituting the microparticles. The work presented is seen useful for anisotropic particle synthesis, local wetting control, lithography, and morphological control of functional materials.

Microfluidic synthesis of anisotropic particles from Janus drop by in situ photopolymerization

Purpose This study presents a microfluidic method to generate anisotropic particles from Janus drop with high flexibility to control their shapes by in situ photopolymerization.

Ecofriendly Synthesis of Anisotropic Gold Nanoparticles: A Potential Candidate of SERS Studies

Ecofriendly synthesis of nanoparticles has been inspiring to nanotechnologists especially for biomedical applications. Moreover, anisotropic particle synthesis is an attractive option due to decreased symmetry of such particles often leads to new and unusual chemical and physical behaviour. This paper reports a single-step room-temperature synthesis of gold nanotriangles using a cheap bioresource of reducing and stabilizing agentPiper betleleaf extract. On treating aqueous chloroauric acid solution withPiper betleleaf extract, after 12 hr, complete reduction of the chloroaurate ions was observed leading to the formation of flat and single crystalline gold nanotriangles. These gold nanotriangles can be exploited in photonics, optical coating, optoelectronics, magnetism, catalysis, chemical sensing, and so forth, and are a potential candidate of SERS studies.

Biocompatible Polymers: Structurally Controlled Bio-hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells (Adv. Mater. 48/2009).

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured biohybrid materials, report Joerg Lahann and co-workers on p. 4920. Functional polarity due to two biologically distinct hemispheres has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Structurally Controlled Bio-hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells.

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured bio-hybrid materials. Functional polarity due to two biologically distinct hemispheres has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Direct Synthesis of Anisotropic Metal Particles by Ink Jet Printing Technique

Here we report the synthesis of nanoparticles with aspect ratios of up to five by synthesis in small concentrated volumes of reactants using an ink-jet printer. Silver and gold nanoparticles were synthesized rapidly on transparent sheets using a commercial ink jet printer. A commercial inkjet printer was modified by replacing conventional inks with different reactants including silver nitrate, ammonium-complex silver, gold chloride reduced by ascorbic acid. The reaction was allowed to occur directly on the substrate within a short reaction time and confined reaction volume defined by the droplet size on the substrate. The nanoparticles and microrods formed on the substrate depend on pH and ionic concentrations of the solutions. The pH of the solutions is an important factor controlling the aspect ratio of microrods. When the concentration of silver ions in the reactant solution was increased the number of particles deposited on the substrate increased subsequently. Anisotropic particles could be formed uniformly over very large area surfaces (1mm x 20mm). This method can be suitable for rapid synthesis of anisotropic particles for potential application in metal-enhanced fluorescence sensing, antibacterial coating, anti reflection coatings, amongst others.

Formation of Biphasic Janus Droplets in a Microfabricated Channel for the Synthesis of Shape‐Controlled Polymer Microparticles

A microfluidic approach is developed for the synthesis of anisotropic particles based on the flow of two immiscible organic phases, a polymerizable phase and a non-polymerizable phase, in a co-flowing aqueous stream within a microchannel. The anisotropic shape originates from the balancing of the interfacial energies between the three phases. The anisotropic particles shown in the figure are obtained by the photopolymerization of the droplets formed in the channels.

Anisotropic particle synthesis in dielectrophoretically controlled microdroplet reactors

The miniaturization of chemical and biological processes in microfluidic devices and bioarrays is a major technological achievement. Microchips performing multiphase material synthesis operations could be a future step in this trend of miniaturizing technology. Here we show how electrically controlled chips can be used for the synthesis and manipulation of new types of particles with advanced structure. The method is based on a technique that allows freely suspended droplets and particles to be entrapped and transported using electric fields. The fields that hold and guide the droplets and particles are applied through arrays of electrodes submerged in the oil. Each of the microdroplets suspended on the surface of fluorinated liquid serves as a microscopic reactor, where the particles are formed by solidification of the carrier droplets. Controlled on-chip assembly, drying, encapsulation and polymerization were used to make anisotropic 'eyeball' and striped particles, polymer capsules and semiconducting microbeads.

Morphological control of particles

Abstract The objective of this review is to highlight the theoretical and practical aspects of particle morphological control. Materials with directional properties are opening new horizons in material science. Structural, optical, and electrical properties can be greatly augmented by the fabrication of composite materials with anisotropic microstructures or with anisotropic particles uniformly dispersed in an isotropic matrix. Examples include structural composites, magnetic and optical recording media, photographic film, and certain metal and ceramic alloys. The new applications and the need for model particles in scientific investigations are rapidly outdistancing the ability to synthesize anisotropic particles with specific chemistries and narrowly distributed physical characteristics (e.g. size distribution, shape, and aspect ratio). Anisotropic particles of many compositions have been produced but only a few (γ-Fe2O3 and AgI) are produced with any degree of chemical and physical control. These two examples are the result of literally decades of study. Unfortunately, the science and technology (mainly the technology) that have evolved are maintained as proprietary information. Thus, while we generally know what systems yield single crystal, anisotropic-shaped particles, we do not know how to make powders of these crystals with the desired control of shape uniformity, aspect ratio and phase composition. Particle shape control is a complex process requiring a fundamental understanding of the interactions between solid state chemistry, interfacial reactions and kinetics, and solution (or vapor) chemistry. During synthesis of other than a large single crystal the parameters controlling crystal growth must be balanced with the requirements for anisotropic powder nucleation and growth. Although there has been considerable progress in large single crystal growth and the synthesis of powders composed of monodispersed, spherical particles, these efforts have not often been transferred to the synthesis of anisotropic particles.