Low Size Polydispersity Research Articles

The drastic influence of the NaBH4 reducing agent on the growth of cobalt nanoparticles and their 3D assemblies

Cobalt nanoparticles are synthesized by chemical reduction in reverse micelles using 6 different products of NaBH4 reducing agent. The nanoparticle size polydispersity strongly depends on the NaBH4 used. With the same synthetic approach, only one product yields to uniform size and shape nanoparticles. This result highlights that the NaBH4 plays a key role in the reproducibility of (1) the synthesis of Co nanoparticles characterized by a low size polydispersity, and (2) their 3D assembly. I stress that this finding can strongly affect not only the development of nanoparticles and their 3D assemblies but also our knowledge concerning the nucleation and growth mechanisms at both the atomic and nanoparticle scales, which can be biased, if we do not account this additional key parameter among all the ones involved in the colloidal synthesis.

Mixed Hyperbranched/Triblock Copolymer Micelle Assemblies: Physicochemical Properties and Potential for Drug Encapsulation

AbstractMixed micelles have numerous advantages while requiring little to no effort in preparation. This study aims to produce mixed micelle nanostructures from a linear triblock copolymer and a hyperbranched random copolymer, and is able to be loaded with the weakly water‐soluble drugs curcumin and indomethacin. Different preparation techniques are employed to produce mixed micelles comprised of Pluronic F127 block copolymer, and hyperbranched poly[(ethylene glycol) methyl ether methacrylate‐co‐lauryl methacrylate], H‐[P(OEGMA‐co‐LMA)], copolymer. Few studies have dabbled in these types of coassemblies, which provides insight into how structural differences of each copolymer can affect the formation of micelles. To determine the properties of the emerging nanostructures in aqueous environments, including their size, homogeneity, and surface charge, different physicochemical techniques are used, such as light scattering and spectroscopic methods. The results reveal that the copolymers combine, and spontaneously self‐assemble into mixed micelle‐like nanostructures in aqueous environments, whereas both systems of neat and drug‐loaded nanostructures exhibit desirable properties such as small average micelle hydrodynamic radii and low size polydispersity indices. The nanostructures that result from the effective encapsulation of curcumin exhibit outstanding stability over 169 days. The fluorescent qualities of curcumin persist after encapsulation, making the novel nanostructures excellent candidates for bioimaging applications.

Modulation of Graphene Interlayer Spacing by Superatoms

Due to the limited variety of natural atoms and the preparation of nanoparticles with low size polydispersity, it is still a challenge to adjust the interesting properties of graphene at the atomic level by changing its interlayer spacing. Here, we demonstrate that superatoms can fill the deficiency by providing adjustable and stable intercalation units between graphene layers, offering effective control of the interlayer distance. Our calculations show that for Au20 superatoms intercalating between graphene interlayers, as their density increases from 2.1 × 10–3 to 4.0 × 10–3 superatom/Å2, the graphene interlayer spacing increases from 9.3 to 11.4 Å. The Au20 maintains to be in a dispersion interaction-dominated physical adsorption state with the graphene layer till the density is decreased to 1.6 × 10–3 superatom/Å2, after which the graphene can crush Au20, resulting in a graphene structure with chemical adsorption of the deformed Au20. This work suggests that superatoms can have an important prospect in membrane separation applications.

Facile synthesis of fluorescent polymer nanoparticles by covalent modification-nanoprecipitation of amine-reactive ester polymers.

Emission wavelength control in fluorescent nanoparticles (NPs) is crucial for their applications. In the case of inorganic quantum dots or dye-impregnated silica NPs, such a control is readily achieved by changing the size of the particles or choosing appropriate fluorescent dyes, respectively. A similar modular approach for controlling the emission wavelength of fluo-rescent polymer NPs, however, is difficult. This article reports on fluorescent polymer NPs, the synthesis of which provides a platform for a modular approach towards the preparation of fluorescent NPs of desired emission wavelength. Atom-transfer radical polymerization (ATRP) is employed to synthesize reactive ester polymers, which are then easily modified with a commercially available dye and subsequently subjected to nanoprecipitation. The resulting NPs, with low size polydispersity, show an enhanced emission quantum yield when compared with the same dye molecules in solution.

Effect of size polydispersity versus particle shape in dense granular media.

We present a detailed analysis of the morphology of granular systems composed of frictionless pentagonal particles by varying systematically both the size span and particle shape irregularity, which represent two polydispersity parameters of the system. The microstructure is characterized in terms of various statistical descriptors such as global and local packing fractions, radial distribution functions, coordination number, and fraction of floating particles. We find that the packing fraction increases with the two parameters of polydispersity, but the effect of shape polydispersity for all the investigated structural properties is significant only at low size polydispersity where the positional and/or orientational ordering of the particles prevail. We focus in more detail on the class of side/side contacts, which is the interesting feature of our system as compared to a packing of disks. We show that the proportion of such contacts has weak dependence on the polydispersity parameters. The side- side contacts do not percolate but they define clusters of increasing size as a function of size polydispersity and decreasing size as a function of shape polydispersity. The clusters have anisotropic shapes but with a decreasing aspect ratio as polydispersity increases. This feature is argued to be a consequence of strong force chains (forces above the mean), which are mainly captured by side-side contacts. Finally, the force transmission is intrinsically multiscale, with a mean force increasing linearly with particle size.

Uniform metal nanoparticles produced at high yield in dense microemulsions

This article demonstrates that bicontinuous microemulsions are optimal templates for high yield production of metal nanoparticles. We have verified this for a variety of microemulsion systems having AOT (sodium bis (2-ethyhexyl) sulphosuccinate) or a fluorocarbon (perfluoro (4-methyl-3,6-dioxaoctane)sulphonate) as surfactant mixed with water and oils like n-heptane or n-dodecane. Several types of metal nanoparticles, including platinum, gold and iron, were produced in these microemulsions having a size range spanning 1.8−17nm with a very narrow size distribution of ±1nm. Remarkably high mass concentrations up to 3% were reached. Size and concentration of the nanoparticles could be varied with the stoichiometries of the reagents that constituted them. The optimization towards high yield while maintaining low size polydispersity is due to the decoupling of the time scales for the precipitation reaction and for coarsening. In actual fact, coalescence is essentially prevented by the immobilization of nanoparticles within the bicontinuous microemulsion structure.

Solid Peptide Nanoparticles - Structural Characterization and Quantification of Cargo Encapsulation

CD3ac, an uncharged and strongly hydrophobic 10 amino acid peptide (Ac-LK(Ac)-LK(Ac)-LK(Ac)-LW-DL-LW-DL-LW-DL-LW-NH2) was synthesized and purified. The peptide readily dissolves in ethanol and--upon solvent exchange to water--assembles into solid spherical particles with diameters of around 500 nm and low size-polydispersity. CD3ac self-assembles in a convenient one-step-process in the absence of a templating two-phase solvent system or any other templating agents. Circular dichroism reveals a gramicidin-like secondary structure, which can be attributed to the presence of D-leucine, whereas LCD3ac, a peptide of identical constitution yet composed entirely of L-amino acids precipitates amorphously. The unacetylated derivative of LCD3ac (LCD3) displays α-helical character in circular dichroism. During the process of bead formation, CD3ac can take up and enrich water-soluble and--insoluble cargo compounds, which is exemplified by the encapsulation of rose bengal (RB) and 5-carboxy-fluorescein (CF), two xanthene derivatives. We confirmed their presence in CD3ac beads by confocal fluorescence microscopy and quantified the encapsulation efficiency by absorption measurements of dissolved RB-containing peptide bead suspensions. Loaded CD3ac beads consist of up to 40 mol-% RB, which corresponds to a logarithmic partition coefficient of 2.95. To the best of our knowledge CD3ac is the first peptide synthesized by Fmoc chemistry which forms solid particles in the nano- and micrometer size range and holds promise for drug delivery applications.

Oxygen-proof fluorescence temperature sensing with pristine C70encapsulated in polymernanoparticles

We report the first successful encapsulation of pristine fullerene C70 in polymer nanoparticles with very low size polydispersity. We obtained water-dispersed polystyrene (PS) nanoparticles with diameters from 60 nm to 190 nm using a miniemulsion polymerization technique. Contrarily to pristine fullerenes, which are insoluble in most solvents and materials, the nanoparticles containing fullerene C70 (PS-C70) are stable in water and can be easily incorporated in different materials. When blended with polyacrylonitrile (PAN), a virtually oxygen-impermeable polymer, the PS-C70 nanoparticles show a strong temperature dependence of the thermally activated delayed fluorescence (TADF) intensity and lifetimes, even when exposed to air. This is the first fluorescence temperature sensor based on TADF that can operate in the presence of oxygen. Unlike other fluorescence temperature sensors, our sensor material is insensitive to oxygen, has emission lifetimes in the millisecond range, and shows a strong emission intensity increase when the temperature increases. This sensor exhibits a very broad sensitivity in a working range from −75 °C to at least 105 °C (based on fluorescence intensity), surpassing the performance of other temperature fluorescence sensors at high temperatures.

Interfacial Synthesis and Widely Controllable Conductivity of Polythiophene Microparticles

Fine polythiophene (PTh) microparticles were successfully synthesized by a novel interfacial polymerization at a dynamic interface between two immiscible solvents, i.e., n-hexane and acetonitrile or nitromethane containing thiophene and oxidant, respectively. The polymerization yield, size, and electrical conductivity of the microparticles are optimized by facilely regulating the medium species, oxidant species, oxidant/monomer ratio, monomer concentration, and polymerization temperature. The microparticles were thoroughly characterized by IR, UV-vis spectroscopy, wide-angle X-ray diffractometry, laser particle-size analyzer, and simultaneous TG-DSC technique. The yield rises with increasing oxidant/monomer ratio, monomer concentration, and polymerization temperature. However, low monomer concentration, low polymerization temperature, and modest oxidant/monomer ratio are all favorable for the formation of the PTh with good, large pi-conjugation and high conductivity. With decreasing the thiophene concentration from 200 to 50 mM at a fixed FeCl3/thiophene molar ratio of 3 at 0 degrees C in hexane/nitromethane biphase system, the PTh obtained exhibits a steadily enhanced conductivity from 10(-12) to 0.01 S cm(-1) and gradually darkening color from crimson to black. Under the same conditions, the PTh obtained in hexane/acetonitrile usually possesses lower yield but higher conductivity than that in hexane/nitromethane. The conductivity will be further enhanced to 1.1 and 4.4 S cm(-1) if the PTh powders are doped in iodine vapor and simply carbonized at 25 through 999 degrees C in nitrogen, respectively. The PTh is fine particles with the number-average diameter of 2.67-3.95 microm and low size polydispersity index between 1.12 and 1.23. The black particles carbonized at 25 to 999 degrees C are much smaller than original PTh particles, with the number-average diameter of 279 nm and size polydispersity index of 1.09. This interfacial approach provides an optimal synthesis of unique PTh microparticles with large pi-conjugation, high conductivity, black color, uniform size, good insolubility, excellent infusibility, high thermostability, and high yield of electrically conducting char at 999 degrees C.

Synthesis of Well-Defined and Low Size Distribution Cobalt Nanocrystals: The Limited Influence of Reverse Micelles

Cobalt nanocrystals are produced in cobalt(II) bis(2-ethylhexyl)sulfosuccinate (Co(AOT)2) reverse micelles. It is found that their size distribution is related to the volume of reducing agent added to the micellar system. At a low volume of reducing agent, the micelles play the role of nanoreactors in which take place the nucleation and growth of cobalt. In the supersaturate regime, that is, at a high volume of reducing agent, micelles are destroyed. In the first case, the nanocrystal size polydispersity is about 29%, while in the latter case, it can decrease to 8%. This low size polydispersity has to be related on one hand to the excess of the reducing agent that modifies the nucleation and growth processes and on the other hand to the structural and chemical evolutions of the micellar system. To obtain well-defined two-dimensional superlattices, the size distribution needs to be less than 13%.