Addition of Zinc Sulfide Shells to Semiconducting Nanoparticles and its Effect on the Nanoparticle Fluorescence Emission Properties

The addition of a ZnS shell to CdSe and CdS quantum dot cores was explored using various methods. Spectrophotometry was used to assess the success of ZnS overcoating, which produces both an increase in overall fluorescence and decrease in particle size distribution. A new method was developed, involving preheating of the zinc and sulfide precursor solutions, resulting in CdSe(ZnS) particles with improved fluorescence and a more uniform shell coating from oleylamine-capped CdSe core particles.

Investigating The Fate Of Positively Charged Nanoparticles In A Soil Environment

The recent increase in the amount of nanoparticles incorporated into commercial products is accompanied by a rising concern of the fate of these nanoparticles. Once released into the environment, it is inevitable that the nanoparticles will come into contact with the soil, introducing them to various routes of environmental contamination. One route that was explored in this research was the interaction between nanoparticles and clay minerals. In order to better define the interactions between clay minerals and positively charged nanoparticles, in situ atomic force microscopy (AFM) was utilized. In situ AFM experiments allowed interactions between clay minerals and positively charged nanoparticles to be observed in real time. The preliminary results demonstrated that in situ AFM was a reliable technique for studying the interactions between clay minerals and positively charged nanoparticles and showed that the nanoparticles affected the swelling (height) of the clay quasi-crystals upon exposure. The preliminary AFM data were complemented by batch study experiments which measured the absorbance of the nanoparticle filtrate after introduction to clay minerals in an effort to better determine the mobility of the positively charged nanoparticles in an environment with significant clay contribution. The results of the batch study indicated that the interactions between clay minerals and positively charged nanoparticles were size dependent and that the interactions of the different size nanoparticles with the clay may be occurring to different degrees. The degree to which the different size nanoparticles were interacting with the clay was further probed using FTIR (Fourier transform infrared) spectroscopy experiments. The results of these experiments showed that interactions between clay minerals and positively charged nanoparticles were size dependent as indicated by a change in the FTIR spectra of the nanoparticles upon introduction to clay.

Multiscale Characterization of Acrylic Bone Cement Modified with Functionalized Mesoporous Silica Nanoparticles

Acrylic bone cement is widely used to anchor orthopedic implants to bone and mechanical failure of the cement mantle surrounding an implant can contribute to aseptic loosening. In an effort to enhance the mechanical properties of bone cement, a variety of nanoparticles and fibers can be incorporated into the cement matrix. Mesoporous silica nanoparticles (MSNs) are a class of particles that display high potential for use as reinforcement within bone cement. Therefore, the purpose of this study was to quantify the impact of modifying an acrylic cement with various low-loadings of mesoporous silica. Three types of MSNs (one plain variety and two modified with functional groups) at two loading ratios (0.1 and 0.2 wt/wt) were incorporated into a commercially available bone cement. The mechanical properties were characterized using four-point bending, microindentation and nanoindentation (static, stress relaxation, and creep) while material properties were assessed through dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, FTIR spectroscopy, and scanning electron microscopy. Four-point flexural testing and nanoindentation revealed minimal impact on the properties of the cements, except for several changes in the nano-level static mechanical properties. Conversely, microindentation testing demonstrated that the addition of MSNs significantly increased the microhardness. The stress relaxation and creep properties of the cements measured with nanoindentation displayed no effect resulting from the addition of MSNs. The measured material properties were consistent among all cements. Analysis of scanning electron micrographs images revealed that surface functionalization enhanced particle dispersion within the cement matrix and resulted in fewer particle agglomerates. These results suggest that the loading ratios of mesoporous silica used in this study were not an effective reinforcement material. Future work should be conducted to determine the impact of higher MSN loading ratios and alternative functional groups. (C) 2014 Elsevier Ltd. All rights reserved.