Microgel/SiO2 hybrid colloids prepared using a water soluble silica precursor

In the present work we demonstrate that functional polymer microgels may act as smart self-catalyzing system inducing controlled formation of silica nanoparticles inside the polymer network and formation of hybrid colloids. We synthesized a water soluble silica precursor PEG-PEOS via post-modification of hyperbranched poly(ethoxysiloxane) (PEOS) with poly(ethylene glycol) monomethyl ether. We used poly(N-vinylcaprolactam)-based microgel functionalized with imidazole and β-diketone groups as a matrix for biomimetic deposition of silica. Composite microgel particles containing silica nanoparticles (up to 20 wt.-%) have been prepared by simultaneous PEG-PEOS conversion and silica deposition in the microgels. TEM studies indicate the infiltration of silica nanoparticles (～10 nm) inside the corona region of the microgels due to the strong acid–base interaction between the acidic silica and basic imidazole groups. The resulting composite particles were found to be colloidally stable and no aggregation was observed even after months of storage. The incorporation of silica nanoparticles increased the rigidity of the microgel particles and reduced their thermal sensitivity.     

Tuneable catalytic properties of hybrid microgels containing gold nanoparticles

A novel type of submicrometer-sized hybrid microgels containing gold nano-particles (AuNPs) has been tested as catalyst in reduction of 4-nitrophenol in aqueous medium. The influence of microgel concentration, gold content, as well as temperature of reaction medium on kinetics of 4-nitrophenol reduction process has been investigated. The pseudo-first-order kinetics was used to evaluate the catalytic reaction rate. It has been demonstrated that reaction rate of 4-nitrophenol reduction can be accelerated if the concentration of microgel in the reaction system or amount of gold nanoparticles loaded into microgels increases. Increase of reaction temperature resulted in rapid increase of reduction rate. Compared to pure gold nano-particles hybrid microgels at similar conditions reduce the activation energy of reduction process by a factor of 2. This indicates that localization of AuNPs within microgel template prevents their aggregation and therefore high catalytic activity can be preserved independently from reaction conditions. Additionally, polymeric template provides suitable environment for better mass transfer in present system that improves the catalyst efficiency.     

Trees as reservoirs for amphibole fibers in Libby, Montana

Tree bark and core samples were collected from areas surrounding the asbestos-contaminated vermiculite mine in Libby, MT. These samples were collected to provide preliminary data in support of a proposed study to determine if trees can serve as reservoirs for amphibole fibers and to determine if there is a potential for exposure to those that harvest contaminated wood in the Libby mine area, specifically during firewood harvesting and commercial logging. Initially, three sets of samples were taken both within and directly outside of the EPA restricted area surrounding the mine site. Based on the results of the initial samples, a follow-up sampling program was conducted both in the town of Libby and directly outside the city limits. Gravimetric reduction of a tree core sample did not indicate the presence of amphibole fibers. However, transmission electron microscopy analysis of bark samples collected near the vermiculite mine yielded substantial amphibole fiber concentrations ranging from 41 million to 530 million fibers/g of bark. In addition, a bark sample collected approximately 7 miles west of the town next to a railroad line had concentrations of 19 million fibers/g. A conversion of these mass-based concentrations to areal concentrations (to reflect surface area contamination) revealed concentrations in excess of 100 million amphibole fibers/cm(2). These preliminary results suggest that trees in the Libby valley and along vermiculite shipping corridors can serve as reservoirs for amphibole fibers, and that a potential for exposure exists for those who harvest contaminated wood.     

A comparison of dispersing media for various engineered carbon nanoparticles

Background  

With the increased manufacture and use of carbon nanoparticles (CNP) there has been increasing concern about the potential toxicity of fugitive CNP in the workplace and ambient environment. To address this matter a number of investigators have conducted in vitro and in vivo toxicity assessments. However, a variety of different approaches for suspension of these particles (culture media, Tween 80, dimethyl sulfoxide, phosphate-buffered saline, fetal calf serum, and others), and different sources of materials have generated potentially conflicting outcomes. The quality of the dispersion of nanoparticles is very dependent on the medium used to suspend them, and this then will most likely affect the biological outcomes.     

Thermo-sensitive poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate) microgels: 2. Incorporation of polypyrrole

In a previous paper [Polymer (2003) in press DOI: 10.1016/j.polymer.2003.09.037] polymeric temperature-sensitive microgels were prepared by surfactant-free emulsion co-polymerization of N-vinylcaprolactam (VCL) and acetoacetoxyethyl methacrylate (AAEM). In the present work, VCL/AAEM microgels were used as a template for oxidative polymerization of pyrrole (Py). It was found that pyrrole polymerization takes place directly in microgel structure leading to composite particles. Influence of microgel structure and amount of incorporated polypyrrole (PPy) on particle properties is discussed. Obtained stable composite microgels show similar thermal sensitivity as VCL/AAEM particles with fully reversible collapse-swelling properties.     

Modeling real-time communication systems: Practices and experiences in Motorola

Visual modeling languages and techniques have been increasingly adopted for software specification, design, development, and testing. With the major improvements of UML 2.0 and tools support, visual modeling technologies have significant potential for simplifying design, facilitating collaborations, and reducing development cost. In this paper, we describe our practices and experiences of applying visual modeling techniques to the design and development of real-time wireless communication systems within Motorola. A model-driven engineering approach of integrating visual modeling with development and validation is described. Results, issues, and our viewpoints are also discussed.