PEG-POSS assisted facile preparation of amphiphilic gold nanoparticles and interface formation of Janus nanoparticles.

A general approach to transfer water-soluble nanoparticles with different shapes, sizes, and surface charges into organic solvents, retaining their surface charge properties was developed, and its application in fabrication of hybrid Janus particles with opposite charges in solution was also demonstrated.

Self-assembly of brush-like poly[poly(ethylene glycol) methyl ether methacrylate] synthesized via aqueous atom transfer radical polymerization.

Self-assembly of brush-like well-defined poly[poly(ethylene glycol) methyl ether methacrylate] homopolymers, abbreviated as P(PEGMA-475) and P(PEGMA-1100) is investigated in aqueous solution by employing dynamic/static light scattering (DLS/SLS) and transmission electron microscopy (TEM), whereas 475 and 1100 is molar mass of the respective PEGMA macromonomer. The mentioned brush-like homopolymers are synthesized by aqueous ATRP at room temperature. The critical association concentration (CAC) of the synthesized polymers in water depends on the length of the PEG side chains but not on the overall molar mass of the polymer. Thus, approximately the same CAC of approximately 0.35 mg/mL is estimated for various P(PEGMA-1100) samples, and approximately 0.7 mg/mL is estimated for P(PEGMA-475) series. All the investigated P(PEGMA-1100) samples form multimolecular micelles in aqueous solution, where the hydrodynamic size (Rh) and the aggregation number (Nagg) of micelles decreases as the molecular weight of P(PEGMA-1100) increases. This can be attributed to the increased steric hindrances between the PEG side chains in corona of micelles formed by higher molar mass P(PEGMA-1100). The tendency of micelle formation by samples of P(PEGMA-475) series is significantly lower than that of P(PEGMA-1100) series, as demonstrated by their significantly higher CAC and micelles of lower Nagg. The Rh of micelles does not depend strongly on polymer concentration, which suggests that these micelles are formed via the closed association model. Micelles formed by P(PEGMA-1100) series slightly shrink with increase in temperature from 25 to 60 degrees C, while those of P(PEGMA-475) series are found to be insensitive to the same temperature variation. Finally, TEM is carried out to visualize the formed micelles after transferring the aqueous solution to carbon film.

Light scattering and luminescence studies on self-aggregation behavior of amphiphilic copolymer micelles.

The self-aggregation behavior of three amphiphilic graft copolymers, oligo(9,9-dihexyl)fluorence-graft-poly(ethylene oxide) (OHF-g-PEO), with different architectures was studied by dynamic and static light scattering (DLS and SLS) in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of self-assembled polymeric micelles was confirmed by SLS and TEM. DLS and SLS analyses showed that the architecture of graft copolymers has a dramatic effect on critical aggregation concentration (CAC), micelle size distribution, apparent aggregation number (Nagg app), and apparent molecular weight of polymer aggregates (Mw,agg app). An architecture-dependent excimer emission, resulting from the pi-pi stacking of the oligofluorene backbones, was also observed from the photoluminescence spectra of the micelle aqueous solutions, which indicated a strong intermolecular interaction among the polymeric molecules. The excimer emission was further investigated by time-resolved fluorescence spectroscopy.

Dynamic and static light scattering studies on self-aggregation behavior of biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) triblock copolymers in aqueous solution.

The self-aggregation behavior of two amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer samples with nearly identical PHB block lengths but different PEO block lengths, PEO-PHB-PEO(2000-810-2000) and PEO-PHB-PEO(5000-780-5000), was studied with dynamic and static light scattering (DLS and SLS), in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of polymeric micelles by the two PEO-PHB-PEO triblock copolymers was confirmed with fluorescence technique and TEM. DLS analysis showed that the hydrodynamic radius (R(h)) of the monodistributed polymeric micelles increased with an increase in PEO block length. The relative thermostability of the triblock copolymer micelles was studied by SLS and DLS at different temperatures. The aggregation number and the ratio of the radius of gyration over hydrodynamic radius were found to be independent of temperature, probably due to the strong hydrophobicity of the PHB block. The combination of DLS and SLS studies indicated that the polymeric micelles were composed of a densely packed core of hydrophobic PHB blocks and a corona shell formed by hydrophilic PEO blocks. The aggregation numbers were found to be approximately 53 for PEO-PHB-PEO(2000-810-2000) micelles and approximately 37 for PEO-PHB-PEO(5000-780-5000) micelles. The morphology of PEO-PHB-PEO spherical micelles determined by DLS and SLS measurements was further confirmed by TEM.

Supramolecular assembled nanostructure containing cubic silsesquioxane in aqueous solution.

Micellization and aggregation behavior of amphiphilic cubic silsesquioxane-poly(ethylene oxide) (CSSQ-PEO) in aqueous solution was studied by Dynamic and Static Light Scattering (DLS and SLS), and Transmission Electron Microscopy (TEM). The effects of CSSQ-PEO concentration and temperature on particle size were also investigated. Above the critical aggregation concentration (CAC), a combination of unassociated single micelle and micellar aggregates is observed up to a certain level of CSSQ-PEO concentration as determined by DLS and TEM studies. The size of unassociated single micelles are found to be independent of CSSQ-PEO concentration while that of the micellar aggregates become larger at higher concentration due to the aggregation growth. Both studies revealed that a small CSSQ core is surrounded by PEO corona and found self-assembled nanostructure of CSSQ-PEO in aqueous solution. The molecular weight of micellar aggregates (Mw,agg), radius of gyration (Rg), and apparent aggregation number (Nagg) were evaluated by SLS measurement. The decrease in the particle size (described by hydrodynamic diameter: Dh) upon increasing temperature was observed because of the diminishing hydrophilicity of PEO. Surprisingly, Rg is also decreased at higher temperature assuming the dissociation of micellar aggregates by repulsive forces due to the crowding effect. The encapsulation property of CSSQ-PEO to model drug has also been studied. Our preliminary results from DLS and TEM studies showed the formation of CSSQ-PEO nanospheres containing drug in aqueous solution. The size of the drug loaded CSSQ-PEO nanospheres are found to be larger (250-300 nm) than that of the core-corona CSSQ-PEO micellar aggregates (approximatly 180 nm) in dilute aqueous solution.

Aggregation-driven growth of size-tunable organic nanoparticles using electronically altered conjugated polymers.

A novel class of monodisperse conjugated polymer nanoparticles have been readily prepared by the facile reprecipitation of poly{1,3-bis[2-(3-alkylthienyl)]azulene} or poly{1,3-bis[2-(3-alkoxythienyl)]azulene}. The multicomponent poly(bithiophene-alt-azulene) macromolecules were efficiently self-assembled into a wide range of size-tunable nanoparticles from a few tens to five hundred nanometers via the hydrophobic and pi-stacking effects in the mixed chloroform/methanol solutions. Electronically altered polymer structures with different alkyl or alkoxy substitutes exhibited variable self-assembling behaviors to precisely tune the size and the optical/electronic properties of nanoparticles. A strong size dependence of continuous bathochromic absorption and significant enhanced emission were observed with the increase of particle size. A linear relationship between the absorption or fluorescence intensities and the particle size was demonstrated as well, and this is very useful to probe the intermolecular interactions and the size evolutions of conjugated polymer nanoparticles. After the size-dependent optical and electronic properties are created, they can be further optimized to improve the performance of materials prior to the use in novel organic nanodevices in a cost-effective way.