Monodisperse Colloids Research Articles

Optimizing the Synthesis of Monodisperse Colloidal Spheres Using Holographic Particle Characterization.

Holographic particle characterization measures the sizes and compositions of individual colloidal particles dispersed in fluid media and rapidly amasses statistics on the distributions of these properties, even for complex heterogeneous dispersions. This information is useful for analyzing and optimizing protocols for synthesizing colloidal particles. We illustrate how holographic characterization can guide process design through a case study on a particularly versatile model system composed of an aqueous dispersion of micrometer-scale spheres synthesized from the organosilane monomer 3-(trimethoxysilyl)propyl methacrylate.

Size-Selective Optical Printing of Silicon Nanoparticles through Their Dipolar Magnetic Resonance

Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g., metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- and microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles.

Simple reactor for the synthesis of silver nanoparticles with the assistance of ethanol by gas–liquid discharge plasma

Atmospheric pressure plasma technology is gaining increasing importance because it is a simple and tunable synthesis process for the production of metallic nanoparticles. In addition to the development of the power supply, improving the reactor is also one of the main strategies to enhance the utility. In this study, a simple reactor for the gas–liquid discharge plasma induced by argon gas was applied to synthesize silver nanoparticles from silver nitrate (AgNO3) in solution. An AC power supply with a peak voltage of 3.5 kV was used. The frequency and on-time were set to 50 kHz and 2.5 μs, respectively. The oscilloscope showed that the rising time was approximately 2 μs. The ethanol was used as the source for the reactive reducing agent. No more additional components existed in the solution during the discharge and neither of the electrodes was in contact with the treated solution. The temperature increased by 10 °C within 1 min without a cooling system. Carbon was the main impurity and was expected to be produced from the decomposition of the organics under the plasma. The elevated temperature decreased the organic by-products by evaporation and could also decrease the production of carbon. Transmission electron microscopy showed that the spherical silver nanoparticles with a size of approximately 10 nm were synthesized with a crystal structure and that a low concentration of ethanol prefers the production of the mono-dispersed colloid.

Shear-Thickening Behavior of Concentrated Monodispersed Colloidal Suspensions

Shear-Thickening Behavior of Concentrated Monodispersed Colloidal Suspensions

Rheological Behavior of Concentrated Monodispersed Colloidal Suspensions

Rheological Behavior of Concentrated Monodispersed Colloidal Suspensions

Design strategies for shape-controlled magnetic iron oxide nanoparticles.

Ferrimagnetic iron oxide nanoparticles (magnetite or maghemite) have been the subject of an intense research, not only for fundamental research but also for their potentiality in a widespread number of practical applications. Most of these studies were focused on nanoparticles with spherical morphology but recently there is an emerging interest on anisometric nanoparticles. This review is focused on the synthesis routes for the production of uniform anisometric magnetite/maghemite nanoparticles with different morphologies like cubes, rods, disks, flowers and many others, such as hollow spheres, worms, stars or tetrapods. We critically analyzed those procedures, detected the key parameters governing the production of these nanoparticles with particular emphasis in the role of the ligands in the final nanoparticle morphology. The main structural and magnetic features as well as the nanotoxicity as a function of the nanoparticle morphology are also described. Finally, the impact of each morphology on the different biomedical applications (hyperthermia, magnetic resonance imaging and drug delivery) are analysed in detail. We would like to dedicate this work to Professor Carlos J. Serna, Instituto de Ciencia de Materiales de Madrid, ICMM/CSIC, for his outstanding contribution in the field of monodispersed colloids and iron oxide nanoparticles. We would like to express our gratitude for all these years of support and inspiration on the occasion of his retirement.

Self-assembly of colloidal Poly(St-MMA-AA) core/shell photonic crystals with tunable structural colors of the full visible spectrum

This study used the copolymer emulsion method to synthesize colloidal monodisperse core/shell microspheres composed of the poly(styrene-co-methyl methacrylate-co-acrylic acid) [Poly(St-MMA-AA)]. Colloidal photonic crystal (CPhC) films have prepared by using polymer composite microspheres and successfully fabricated via natural sedimentation. The synthesized results of polymer composite microsphere exhibited uniform and good morphology. The resultant of CPhC color films demonstrated vividly structural colors due to 3D CPhC nanostructures. The structural colors over full visible spectra could be tuned by controlling the filling factor of crystals and diameter of microspheres according to the Bragg law. Additionally, the structural color of Poly(St-MMA-AA) CPhC films has measured under the standard colorimetric system. This study demonstrated a approach to fabricate tunable structural color for numerous applications.

One-Pot Preparation of Physical Hydrogel-Based Photonic Crystal

We developed a one-pot method for the fabrication of hydrogel-based photonic crystal (PC) materials. An array of monodisperse colloids was self-assembled within a polymer solution, which generates a visible light diffractable photonic mixture. This mixture was molded and gelated into a hydrogel PC material by freeze-thaw treatment. Drug release as well as the structure colour changing properties of the PC hydrogels were discussed, and the experiment results revealed that our one-pot design and the associated modification approach has potential in efficient fabrication of PC materials.

Unexpected stability of aqueous dispersions of raspberry-like colloids

Aqueous colloidal suspensions, both man-made and natural, are part of our everyday life. The applicability of colloidal suspensions, however, is limited by the range of conditions over which they are stable. Here we report a novel type of highly monodisperse raspberry-like colloids, which are prepared in a single-step synthesis that relies on simultaneous dispersion and emulsion polymerisation. The resulting raspberry colloids behave almost like hard spheres. In aqueous solutions, such prepared raspberries show unexpected stability against aggregation over large variations of added salt concentrations without addition of stabilisers. We present simple Derjaguin–Landau–Verwey–Overbeek (DLVO) calculations performed on raspberry-like and smooth colloids showing that this stability results from our raspberries’ unique morphology, which extends our understanding of colloidal stability against salting. Further, the raspberries’ stability facilitates the formation of superspheres and thin films in which the raspberry colloids self-assemble into hexagonally close-packed photonic crystals with exquisite reproducibility.

Monodisperse Colloidal Metal Nanoparticles to Core–Shell Structures and Alloy Nanosystems via Digestive Ripening in Conjunction with Solvated Metal Atom Dispersion: A Mechanistic Study

Co-digestive ripening of two distinct metal nanoparticles is an exceptional method for the colloidal synthesis of core–shell heterostructures. In this report, a detailed investigation of the underlying mechanism by which surfactant molecule assisted interatomic transfer between two metal nanoparticles occurs has been described using gold/silver as a model system. Core–shell nanoparticles with gold in the core and silver in the shell in the size regime of 6.9 ± 1.8 nm were obtained by conducting the codigestive ripening of polydispersed particles of Au–pentanone and Ag–pentanone colloids in the presence of hexadecylamine as a capping agent used in the molar ratio of 1:30 with respect to metal. The progress of the formation of core–shell nanoparticles has been monitored using UV–visible spectroscopy and transmission electron microscopy. Detailed analysis of the nature of Au@Ag core–shell nanoparticles has been done with the help of HAADF-STEM technique, point-EDS analysis, elemental line scanning technique,...

Three-Dimensional Superlattice of PbS Quantum Dots in Flakes.

In the last two decades, many experiments were conducted in self-organization of nanocrystals into two- and three-dimensional (3D) superlattices and the superlattices were synthesized and characterized by different techniques, revealing their unusual properties. Among all characterization techniques, X-ray diffraction (XRD) is the one that has allowed the confirmation of the 3D superlattice formation due to the presence of sharp and intense diffraction peaks. In this work, we study self-organized superlattices of quantum dots of PbS prepared by dropping a monodispersed colloidal solution on a glass substrate at different temperatures. We showed that the intensity of the low-angle XRD peaks depends strongly on the drying time (substrate temperature). We claim that the peaks are originated from the 3D superlattice. Scanning electron microscopy images show that this 3D superlattice (PbS quantum dots) is formed in flake’s shape, parallel to the substrate surface and randomly oriented in the perpendicular planes.

Impact of Varying the Concentration of Tetraethyl-OrthoSilicate on the Average Particle Diameter of Monodisperse Colloidal Silica Spheres

In this study, spherical Silica particles with narrow size distribution were prepared by hydrolysis of Tetraethyl OrthoSilicate (TEOS) in Ethanol and the presence of ammonia based on the Stober method. The average particle diameter and monodispersity were controlled by varying the concentration of TEOS. Microscopic analysis showed that a smaller average particle diameter and good degree of monodispersity can be obtained by decreasing the concentration of TEOS.

Functional Polymer Opals and Porous Materials by Shear-Induced Assembly of Tailor-Made Particles.

Photonic band-gap materials attract enormous attention as potential candidates for a steadily increasing variety of applications. Based on the preparation of easily scalable monodisperse colloids, such optically attractive photonic materials can be prepared by an inexpensive and convenient bottom-up process. Artificial polymer opals can be prepared by shear-induced assembly of core/shell particles, yielding reversibly stretch-tunable materials with intriguing structural colors. This feature article highlights recent developments of core/shell particle design and shear-induced opal formation with focus on the combination of hard and soft materials as well as crosslinking strategies. Structure formation of opal materials relies on both the tailored core/shell architecture and the parameters for polymer processing. The emphasis of this feature article is on elucidating the particle design and incorporation of addressable moieties, i.e., stimuli-responsive polymers as well as elaborated crosslinking strategies for the preparation of smart (inverse) opal films, inorganic/organic opals, and ceramic precursors by shear-induced ordering.

Hydrogen Bonding Directed Colloidal Self‐Assembly of Nanoparticles into 2D Crystals, Capsids, and Supracolloidal Assemblies

AbstractSelf‐assembly of colloidal building blocks, like metal nanoparticles, is a rapidly progressing research area toward new functional materials. However, in‐depth control of the colloidal self‐assembly and especially hierarchical self‐assembly is difficult due to challenges in controlling the size dispersities, shape/morphology, directionalities, and aggregation tendencies. Using either polydispersed or narrow‐size dispersed nanoparticles, considerable progress has been achieved over the past few years. However, absolutely monodisperse nanoparticles could allow new options for rational designs of self‐assemblies. Therein, atomically precise monolayer protected nanoclusters (d &lt; 3 nm) have recently been synthesized with well‐defined metal cores and surface ligands. Their dispersion behavior is commonly tuned by surfactant‐like ligands. Beyond that, this study deals with approaches based on ligand‐driven supramolecular interactions and colloidal monodispersity until atomic precision to tune the colloidal self‐assembly and hierarchy from nanoscale to mesoscopic scale. Therein colloidal packing to self‐assembled 2D crystals and closed virus capsid‐inspired shells provide relevant research goals due to ever increasing potential of 2D materials and encapsulation. This study addresses the hydrogen bonding (H‐bonding) directed self‐assembly of atomically precise gold and silver nanoparticles and narrow size dispersed cobalt nanoparticles to free‐standing 2D colloidal nanosheets, nanowire assemblies, capsid‐like colloidal closed shells, as well as higher order structures.

The impact of fines mobilization on CO2 injectivity: An experimental study

Adequate well injectivity is required to inject large volumes of CO2 through minimum number of wells. Presently, salt precipitation is considered the main CO2 injectivity impairment mechanism in deep saline reservoirs. However, mobilization of formation fines, generated from CO2-brine-rock reactions, could plug the rock and induce CO2 injectivity impairment. The unique gas-like viscosity and liquid-like density of CO2, the drying effect of supercritical CO2 and the high injection flow rates required to meet emission reduction targets, demands extension of the current knowledge base to adequately understand the mechanisms and impact of fines mobilization under typical CO2 injection conditions.The impact of fines mobilization on CO2 injectivity was investigated by flooding sandstone cores initially saturated with mono-disperse colloid suspensions with dry supercritical CO2. We found that about 0.5wt.% particle concentration in the pore fluid reduced CO2 injectivity by over 80 per cent. CO2 injectivity impairment increased with increasing particle concentration and CO2 injection flow rate. Initial rock permeability and average particle size was also found to influence particle entrapment. Attempt was made to quantify the relative importance of fines mobilization and salt precipitation. We also found that, about 0.3wt.% particle concentration in the pore fluid, induced over two-fold injectivity impairment compared to about 10wt.% of total dissolved salt in the formation water.Since most of the current works assumes CO2 injectivity is mainly impaired by salt precipitation, the present findings serves as a foundation to reconsider the contribution of transport effects such as fines mobilization.

Formation of 2D and 3D superlattices of silver nanoparticles inside an emulsion droplet

This work is aimed at the formation of 2D and 3D superlattices (SL) of silver nanoparticles inside an emulsion droplet. The monodisperse nanoparticles required for SL formation were prepared by a digestive ripening technique. Digestive ripening is a post processing technique where polydisperse colloids are refluxed with excess surface-active ligands to prepare a monodisperse colloid. More uniform silver nanoparticles (~3.6 ± 0.5 nm) were formed by slow evaporation of organosols on a carbon-coated copper grid. The best 3D silver superlattices have been formed using an oil in water (o/w) emulsion method by aging the monodisperse particles in a confined environment like o/w emulsion at different temperatures ranging from 5 °C–4 °C. The kinetics of the formation of superlattices inside an emulsion droplet were investigated by controlling various parameters. The kinetics were found to be dependent on the emulsion aging period (30 d) and storage temperature of the emulsion (−4 °C).

Colloidal Crystal Lasers from Monodisperse Conjugated Polymer Particles via Bottom-Up Coassembly in a Sol-Gel Matrix.

The potential of colloidal crystals for applications in optics and photonics has been recognized since the description of spontaneous self-assembly of monodisperse colloids into periodic opaline geometries. Provided with a laser gain medium, these direct assemblies generate optical feedback and have prospective use as lasers or frequency converters; however, problems associated with the colloidal crystal integrity and low loading fractions of the gain medium in the self-assembled resonator structure have prevented their realization to date. Here, we circumvent these problems by synthesizing monodisperse conjugated polymer colloids, which consist entirely of gain medium. We coassemble these colloids together with a sol-gel precursor to achieve encapsulated photonic crystals, which can be applied via inkjet printing. These conjugated polymer photonic crystals exhibit single line laser emission upon optical pumping. This technique circumvents time-consuming micro- and nanofabrication steps as well as error-prone backfilling and etching procedures, providing an effortless way to generate laser geometries.

Optimization of Optical Absorption of Colloids of SiO2@Au and Fe3O4@Au Nanoparticles with Constraints.

We study the optical response of monodisperse colloids of core-shell plasmonic nanoparticles and introduce a computational approach to optimize absorption for photothermal applications that require dilute colloids of non-interacting particles with a prescribed volume fraction. Since the volume fraction is held constant, the particle concentration is size-dependent. Optimization is achieved by comparing the absorption spectra of colloids as a function of particle size and structure. We demonstrate the approach via application to colloids of core-shell SiO2@Au and Fe3O4@Au nanoparticles with particle sizes that range from 5–100 nm and with the incident wavelength varying from 600–1200 nm. The absorption spectra are predicted using Mie theory and the analysis shows that there is a unique mix of parameters (core radius, shell thickness, wavelength) that maximize absorption, independent of the value of volume fraction. We show that lossy Fe3O4 cores produce a much broader absorption peak with much less sensitivity to variations in particle structure and wavelength than lossless SiO2 cores. This approach can be readily adapted to colloids of nanoparticles with arbitrary materials, shapes and structure using appropriate numerical methods to compute the absorption spectra. As such, it is useful for the rational design of colloids and process variables for a broad range of photothermal applications.

Thermal tuning the reversible optical band gap of self-assembled polystyrene photonic crystals

Nano-sized polymeric colloidal particles could undergo self-organization into three-dimensional structures to produce desired optical properties. In this research, a facile emulsifier-free emulsion polymerization method was employed to synthesize highly mono-disperse sub-micron polystyrene colloids. A high quality photonic crystal (PhC) structure was prepared by colloidal polystyrene. The reversible thermal tuning effect on photonic band gap position as well as the attenuation of the band gap was investigated in detail. The position of PBG can be tuned from 420nm to 400nm by varying the temperature of the PhC structure, reversibly. This reversible effect provides a reconfigurable PhC structure which could be used as thermo-responsive shape memory polymers.

One-Pot Synthesis of Monodisperse Colloidal Copper-Doped CdSe Nanocrystals Mediated by Ligand–Copper Interactions

We report a one-pot synthesis of high-quality colloidal copper-doped cadmium selenide nanocrystals (Cu+:CdSe NCs) by injection of a mixture of copper iodide (CuI) and trioctylphosphine (TOP) into solutions containing preformed CdSe NCs. This method allows NC doping to be separated from nucleation and growth, thereby simultaneously achieving large size tunability, narrow size dispersion, and exclusively copper-based photoluminescence (PL). The copper doping level is affected by both the reaction time and the relative concentrations of the cadmium precursor, CuI, and TOP. A correlation is demonstrated between the copper dopant concentration and the intensities of the characteristic near-IR PL and midgap absorption bands, both associated with metal-to-ligand (conduction band) charge-transfer (MLCBCT) excitation of Cu+ dopants. Mechanistic studies reveal that Cu2–xSe NCs are easily formed as kinetic intermediates under reaction conditions involving substantial copper and that these NCs then act as a copper so...