Bien Tan

Formation and enhanced biocidal activity of water-dispersable organic nanoparticles

Water-insoluble organic compounds are often used in aqueous environments in various pharmaceutical and consumer products. To overcome insolubility, the particles are dispersed in a medium during product formation, but large particles that are formed may affect product performance and safety. Many techniques have been used to produce nanodispersions-dispersions with nanometre-scale dimensions-that have properties similar to solutions. However, making nanodispersions requires complex processing, and it is difficult to achieve stability over long periods. Here we report a generic method for producing organic nanoparticles with a combination of modified emulsion-templating and freeze-drying. The dry powder composites formed using this method are highly porous, stable and form nanodispersions upon simple addition of water. Aqueous nanodispersions of Triclosan (a commercial antimicrobial agent) produced with this approach show greater activity than organic/aqueous solutions of Triclosan.

Direct Coprecipitation Route to Monodisperse Dual- Functionalized Magnetic Iron Oxide Nanocrystals Without Size Selection

Water-soluble monodisperse superparamagnetic Fe3O4 nanocrystals decorated with two distinct functional groups are prepared in a single-step procedure by injecting iron precursors into a refluxing aqueous solution of a polymer ligand, trithiol-terminated poly(methacrylic acid) (PMAA-PTTM), bearing both carboxylate and thiol functionalities. The ratio of carboxylic acid groups in the polymer-protecting ligand to the iron precursors plays a key role in determining the particle size and particle size distribution. The surface functionalities of the ligands allow post-synthesis modification of the materials to produce water-soluble fluorescent magnetic nanocrystals.

Fluorescent or not? Size-dependent fluorescence switching for polymer-stabilized gold clusters in the 1.1-1.7 nm size range

The synthesis of fluorescent water-soluble gold nanoparticles by the reduction of a gold salt in the presence of a designed polymer ligand is described, the size and fluorescence of the particles being controlled by the polymer to gold ratio; the most fluorescent nanomaterial has a 3% quantum yield, a 1.1 nm gold core and a 6.9 nm hydrodynamic radius.

Photoreductive synthesis of water-soluble fluorescent metal nanoclusters

Water-soluble fluorescent copper, silver and gold nanoclusters with quantum yields of 2.2, 6.8 and 5.3%, respectively, are prepared by a robust photoreduction of their inorganic precursors in the presence of poly (methacrylic acid) functionalized with pentaerythritol tetrakis 3-mercaptopropionate.

Rapid and Reversible Hydrogen Storage in Clathrate Hydrates Using Emulsion-Templated Polymers†

A method for greatly accelerating the storage of gases such as hydrogen in clathrates by supporting the clathrate phase on a highly macroporous emulsion-templated polymer is presented. The gravimetric penalty is low due to the low bulk density of the support, no mechanical mixing is required, and the system is fully recyclable over multiple charge/ discharge cycles.

Size and shape control for water-soluble magnetic cobalt nanoparticles using polymer ligands

We report a synthesis of monodisperse water-soluble magnetic Co nanoparticles using a facile reduction method in aqueous media in the presence of alkyl thioether end-functionalized poly(methacrylic acid) (PMAA-DDT) ligands. The size and shape of the nanoparticles are both tunable by varying synthesis conditions. The size of the spherical nanoparticles can be tuned between 2–7.5 nm by changing the concentration of the polymer. Our synthesis approach also provides a route for producing much larger spherical nanoparticles of 80 nm as well as anisotropic nanorods of 15 × 36 nm. The spherical nanoparticles are superparamagnetic at room temperature. The nanoparticles can be stable in water for up to eight weeks when 0.12 mM PMAA-DTT with molecular weight of 13500 g mol−1 is used as ligand.

Effect of polymer ligand structures on fluorescence of gold clusters prepared by photoreduction

Blue emission fluorescent Au(5) clusters with maximum quantum yield of 20.1% were synthesized by a simple photoreduction method using three specially designed tridentate polymer ligands. The evolution of fluorescent Au nanoclusters (Au NCs) under UV irradiation was studied by fluorescence, UV-Vis and X-ray photoelectron spectroscopic techniques, suggesting that the fluorescence of Au NCs is size-dependent and is associated with the presence of Au(i) ions in the Au NCs. The effect of polymer structure on the fluorescent Au NCs has also been discussed. These highly fluorescent Au NCs have potential applications in the fabrication of optoelectronic devices and light emitting materials.

High-throughput solubility measurements of polymer libraries in supercritical carbon dioxide

A new method has been developed which allows rapid parallel solubility measurements for libraries of materials in supercritical fluids (SCFs). The technique was used to evaluate the solubility of a mixed library of 100 synthetic polymers including polyesters, polycarbonates, and vinyl polymers.

Supercritical Carbon Dioxide as a Green Solvent for Polymer Synthesis

This chapter focuses on the application of supercritical carbon dioxide (scCO 2 ) as a solvent for polymer synthesis. ScCO 2 is an inexpensive, nontoxic, and nonflammable solvent for material synthesis and processing. It has emerged as the most extensively studied environmentally benign medium for organic transformations and polymerization reactions. One of the fundamental issues that should be considered while implementing CO 2 for polymer synthesis or processing is polymer solubility. A number of research groups have synthesized “CO 2 -philic” fluoropolymers or silicone-based materials for use as steric stabilizers in dispersion polymerization, phase transfer agents for liquid–liquid extraction, supports for homogeneous catalysis, and surfactants for the formation of water/CO 2 emulsions and microemulsions. It has been demonstrated that inexpensive poly(ether carbonate) (PEC) copolymers are soluble in CO 2 under moderate conditions and could function as building blocks for inexpensive surfactants, although there are numerous practical difficulties. These hydrocarbon systems involve PECs synthesized by aluminum-catalyzed copolymerization of cyclic ethers with CO 2 . These copolymers were found to be soluble in liquid CO 2 at concentrations of 0.2–1.5% (w/v) at ambient temperatures and pressures in the range 120–160 bar. These statistical copolymers were generated from inexpensive feedstocks and are thus appealing as “building blocks” for cheap surfactants. Similarly, sugar acetates are highly soluble and have been proposed as renewable “CO 2 -philes.” Such materials could, in principle, function as “CO 2 -philic” building blocks for inexpensive ligands and surfactants, but this potential has not been realized and numerous practical difficulties remain. Poly(vinylacetate) (PVAc) has also been shown to exhibit high solubility in CO 2 with respect to other vinyl hydrocarbon polymers, although the polymer is soluble only at relatively low molecular weights under conditions of practical relevance.