We suggest a method for efficient (high-coverage) grafting of organic molecules onto photoluminescent silicon nanoparticles. High coverage grafting was enabled by use of a modified etching process that produces a hydrogen-terminated surface on the nanoparticles with very little residual oxygen and by carefully excluding oxygen during the grafting process. It had not previously been possible to produce such a clean H-terminated surface on free silicon nanoparticles or, subsequently, to produce grafted particles without significant surface oxygen. This allowed us to (1) prepare air-stable green-emitting silicon nanoparticles, (2) prepare stable dispersions of grafted silicon nanoparticles in a variety of organic solvents from which particles can readily be precipitated by addition of nonsolvent, dried, and redispersed, (3) separate these nanoparticles by size (and therefore emission color) using conventional chromatographic methods, (4) protect the particles from chemical attack and photoluminescence quenching, and (5) provide functional groups on the particle surface for further derivatization. We also show, using 1H NMR, that the photoinitiated hydrosilylation reaction does not specifically graft the terminal carbon atom to the surface but that attachment at both the first and second atom occurs.

This article reports on the synthesis of thermosensitive polymer brushes on silica nanoparticles by atom transfer radical polymerization (ATRP) and the study of thermo-induced phase transitions in water. Silica nanoparticles were prepared by the Stöber process and the surface was functionalized by an ATRP initiator. Surface-initiated ATRPs of methoxydi(ethylene glycol) methacrylate (DEGMMA) and methoxytri(ethylene glycol) methacrylate (TEGMMA) were carried out in THF at 40 degrees C in the presence of a free initiator, benzyl 2-bromoisobutyrate. The polymerizations were monitored by 1H NMR spectroscopy and gel permeation chromatography. The hairy hybrid nanoparticles were characterized by thermogravimetric analysis and scanning electron microscopy, and the thermoresponsive properties were investigated by variable temperature 1H NMR spectroscopy and dynamic light scattering. The cloud points of free poly(DEGMMA) and poly(TEGMMA) in water were around 25 and 48 degrees C, respectively. The thermo-induced phase transitions of polymer brushes on silica nanoparticles began at a lower temperature and continued over a broader range (4-10 degrees C) than those of free polymers in water (< 2 degrees C).

A facile method of preparing stable blue-emitting silicon nanoparticles that are dispersible in common organic solvents is presented. Oxidation of yellow-emitting silicon nanoparticles with an organic monolayer grafted to their surface, using either UV irradiation in solution or heating in air, converted them to blue-emitting particles. The evolution of the PL spectrum and infrared absorption spectrum of the particles was followed during the oxidation process. The PL spectrum showed a decrease in the PL emission peak near 600 nm and the appearance and increase in intensity of a PL emission peak near 460 nm rather than a smooth blue shift of the emission spectrum from yellow to blue. The organic monolayer grafted to the particle surface was not degraded by this oxidation process, as demonstrated by FTIR and NMR spectroscopy. Similar results were achieved for particles with styrene, 1-octene, 1-dodecene, and 1-octadecene grafted to their surface, demonstrating that it is the silicon nanocrystal, and not the organic component, that is essential to this process. The organic monolayer allows the nanoparticles to form stable, clear colloidal dispersions in organic solvents and provides for the possibility of further chemical functionalization of the particles. Combined with previous work on organically grafted silicon nanoparticles with green through near-infrared emission, this enables the efficient and scalable preparation of stable colloidal dispersions of organically grafted silicon nanoparticles with emission spanning the entire visible spectrum.

We report the synthesis and thermosensitive properties of well‐defined water‐soluble polyacrylates and polystyrenics with short pendant oligo(ethylene glycol) groups. Four monomers, methoxydi(ethylene glycol) acrylate (DEGMA), methoxytri(ethylene glycol) acrylate (TEGMA), α‐hydro‐ω‐(4‐vinylbenzyl)tris(oxyethylene) (HTEGSt), and α‐hydro‐ω‐(4‐vinylbenzyl)tetrakis(oxyethylene) (HTrEGSt), were prepared and polymerized by nitroxide‐mediated radical polymerization with 2,2,5‐trimethyl‐3‐(1‐phenylethoxy)‐4‐phenyl‐3‐azahexane as an initiator. Kinetics and gel permeation chromatography analysis showed that the polymerizations were controlled processes yielding polymers with controlled molecular weights and narrow polydispersities. All polymers could be dissolved in water, forming transparent solutions, and undergo phase transitions when the temperature was above a critical point. The thermosensitive properties were studied by turbidimetry and variable‐temperature 1H NMR spectroscopy. The cloud points of the polymers of DEGMA, TEGMA, HTEGSt, and HTrEGSt were around 38, 58, 13, and 64 °C, respectively. For all four polymers, the cloud point increased with decreasing concentration and increasing molecular weight in the studied molecular weight range of 5000–30,000 g/mol. The removal of the nitroxide group from the polymer chain end resulted in a higher cloud point. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2454–2467, 2006

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