Block Copolymer-Templated Au@CdSe Core-Satellite Nanostructures with Solvent-Dependent Optical Properties.

In the present work, we report the fabrication and characterization of well-defined core-satellite nanostructures. These nanostructures comprise block copolymer (BCP) micelles, containing a single gold nanoparticle (AuNP) in the core and multiple photoluminescent cadmium selenide (CdSe) quantum dots (QDs) attached to the micelle's coronal chains. The asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP was employed to develop these core-satellite nanostructures in a series of P4VP-selective alcoholic solvents. The BCP micelles were first prepared in 1-propanol and subsequently mixed with AuNPs, followed by gradual addition of CdSe QDs. This method resulted in the development of spherical micelles that contained a PS/Au core and a P4VP/CdSe shell. These core-satellite nanostructures, developed in different alcoholic solvents, were further employed for the time-resolved photoluminescence analysis. It was found that solvent-selective swelling of the core-satellite nanostructures tunes the distance between the QDs and AuNPs and modulates their Förster resonance energy transfer (FRET) behavior. The average lifetime of the donor emission varied from 12.3 to 10.3 nanoseconds (ns) with the change in the P4VP-selective solvent within the core-satellite nanostructures. Furthermore, the distances between the donor and acceptor were also calculated using efficiency measurements and corresponding Förster distances. The resulting core-satellite nanostructures hold promising potential in various fields, such as photonics, optoelectronics, and sensors that utilize the FRET process.

Silica-supported Au@hollow-SiO2 particles with outstanding catalytic activity prepared via block copolymer template approach.

Catalytically active Au@hollow-SiO2 particles embedded in porous silica support (Au@hollow-SiO2@PSS) were prepared by using spherical micelles from poly(styrene)-block-poly(4-vinyl pyridine) block copolymer as a sacrificial template. Drastic increase of the shell porosity was observed after pyrolytic removal of polymeric template because the stretched poly(4-vinyl pyridine) chains interpenetrating with silica shell acted as an effective porogen. The embedding of Au@hollow-SiO2 particles in porous silica support prevented their fusion during pyrolysis. The catalytic activity of Au@hollow-SiO2@PSS was investigated using a model reaction of catalytic reduction of 4-nitrophenol and reductive degradation of Congo red azo-dye. Significantly, to the best of our knowledge, Au@hollow-SiO2@PSS catalyst shows the highest activity among analogous systems reported till now in literature. Such high activity was attributed to the presence of multiple pores within silica shell of Au@hollow-SiO2 particles and easy accessibility of reagents to the catalytically active sites of the ligand-free gold surface through the porous silica support.

Helical packing of nanoparticles confined in cylindrical domains of a self-assembled block copolymer structure.

Theoretical models predict that a variety of self-assembled structures of closely packed spherical particles may result when they are confined in a cylindrical domain. In the present work we demonstrate for the first time that the polymer-coated nanoparticles confined in the self-assembled cylindrical domains of a block copolymer pack in helical morphology, where we can isolate individual fibers filled with helically arranged nanoparticles. This finding provides unique possibilities for fundamental as well as application-oriented research in similar directions.

Control on molecular weight reduction of poly(ε-caprolactone) during melt spinning--a way to produce high strength biodegradable fibers.

Poly(ε-caprolactone) (PCL) is known for its biocompatibility and biodegradability. These features of PCL have resulted into significant academic as well as industrial research interests for use of this polymer in various areas including biomedical and tissue engineering. Three-dimensional porous scaffolds, controlled drug release systems and nerve guides are some of the forms in which this polymer has been used. Despite these forms, fibers made of PCL have not gained much attention due to PCL's low melting point (57-60 °C) and relatively inferior mechanical properties as compared to poly(L-lactide) (PLA). Also the polymer is sensitive to the process conditions of melt spinning which leads to degradation of PCL when subjected to high temperatures in the presence of air or moisture. Here we present an approach in which addition of a bilactone, bis-(ε-caprolactone-4-yl) (BCY), during melt spinning of PCL resulted into monofilament fibers having tenacity as high as 2500 MPa. The cross-linking of PCL which occurred due to BCY transesterification compensated for molecular weight reduction of the polymer under melt spinning conditions. PCL monofilament fibers thus developed have enhanced thermo-mechanical properties and therefore have high potential to be used in tissue engineering applications in the form of sutures, a mesh or a non-woven.