Browsing by Subject "microparticles"
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Item Consolidation of copper and aluminum micro and nanoparticles via equal channel angular extrusion(2009-05-15) Hutchins, Cathleen RuthUltrafine grained (UFG), and nanocrystalline (nc) materials are of interest because of the high strength, compared with coarse grained counterparts. Several current methods to fabricate UFG and nc materials result in samples too small for practical use. In addition, the fabrication of nc materials, in particular, is difficult, and defects in the material causes significant reduction in strength and ductility of these materials. The present study uses Equal Channel Angular Extrusion (ECAE) to produce relatively large consolidates of UFG and nc materials. ECAE has been used to consolidate micro and nanocrystalline powders. The behavior of consolidated pure Cu and aluminum alloys in the nano and micron size were explored. The effects of different routes, extrusion temperature, and post-ECAE processing on microstructure and mechanical behavior were studied. Processing parameters were explored to determine the influence of each parameter on the consolidation performance. The goals of experimenting with different processing parameters were to increase the ductility of the material, while maintaining relatively strong specimens. Comparisons were made with a recently developed powder compaction constitutive model and corresponding simulations. ECAE of microcrystalline powders produced relatively ductile materials, with high strength. Swaging of these consolidated powders produced samples which were softer and less ductile in tension, than the non-swaged samples. ECAE produced effective consolidation of Cu nanoparticles with average sizes of 100 nm, with an ultimate tensile strength of 680 MPa, with a fracture strain as much as 10%, which is higher than previously reported 7% [Haouaoui, 2005].Item Fabrication and Characterization of Poly(2-Hydroxyethyl Methacrylate) Microparticle Sensors(2013-04-24) Philip, MereneOptical biosensors are desired for the monitoring of various biochemical markers, which are relevant indicators in the treatment and diagnosis of diseases. Specifically, luminescence sensors are favorable for optical interrogation since they are highly sensitive to analyte changes and may be implemented in lifetime or intensity-based systems. In order to develop particle-based fluorescent sensors, poly(2-hydroxyethylmethacrylate) (HEMA) microspheres have been fabricated via membrane emulsification and characterized to evaluate the emulsion method and the overall process of tailoring properties to synthesize spheres of specific mean sizes. A pH-sensitive indicator seminaphthorhodafluors-4F 5-(and-6)-carboxylic acid (SNARF) was immobilized within the microspheres, and resulting sensor particles were exposed to various pH buffers to obtain a pH calibration curve based on intensity measurements. PolyHEMA microparticles were fabricated in a systematic study with measured mean sizes ranging from 8-21 um. Optical and scanning electron microscopy images revealed the formation of spherical, porous particles, which were additionally stabilized with polymer coatings. The lowest coefficient of variation value achieved was 50%, indicating the inability to produce monodisperse particles due to the dispersity of pore sizes in the membrane. SNARF was immobilized within the polyHEMA spheres, and fluorescence was observed when exposing the sensors to different pH buffers on a fluorescence microscope. Ratiometric intensity measurements for the sensor particles were obtained on a spectrofluorometer while flowing pH buffers over the immobilized spheres in a reaction chamber. The peak intensity ratio of the microparticle sensors exhibited a change in 0.9 units when decreasing the pH from 8.4 to 5.5. In the future, these pH sensing particles may be implanted alongside glucose sensing materials in order to provide valuable pH information in understanding the immune response to specific biomaterials and sensing components.