Part I of this dissertation describes the synthesis and characterization of solid, copolymeric, magnetic, fluorescent, core-shell, and hollow or foamed micron-sized silicone spheres prepared via ultrasonic spray pyrolysis (USP). Silicones are found in an amazing number of commercial products including cosmetics, sealants, adhesives, lubricants, medical devices, and even food. Despite the prevalence of bulk silicones in today’s society, the synthesis of silicone micromaterials has remained elusive. The same chemical and material characteristics that make silicones ideal for many commercial applications, namely hydrophobicity and low surface tension, cause the droplets in silicone-precursor emulsions to coalesce and aggregate upon curing. Conveniently, the aerosol created in USP, an industrially-scalable synthetic technique used to make relatively monodisperse sub-micron and micron-sized spheres, isolates silicone oligomers into individual droplets during curing. These USP prepared silicone microspheres range from ~500 nm to 2 µm in diameter and are prepared from commercial silicone kits and commercially available oligomers. Synthetic control over size, crosslinking density, composition, and swelling is shown. The solid USP PDMS microspheres are shown to be highly bioinert, are found to be taken into cell cytosol, and show impressive drug loading capacities (as high as 36% by weight). Functional silicone microspheres are obtained by simply adding the appropriate dopant (e.g., fluorescent dye, colloidal Fe3O4, polymeric or ionic salt core material) or changing the silicone oligomers of the precursor solution prior to nebulization. These results demonstrate the versatility and generalizability of this synthetic method and serve as a road-map for the fabrication of silicone microspheres with nearly any desired functionality.Part II of this dissertation describes our efforts in the development of a fully integrated, disposable, and portable gas chromatography column and detector. There is a pressing need for rapid, portable, and inexpensive technology for the on-site detection of gaseous analytes. Significant progress has been made towards this goal through the miniaturization of gas chromatographs (GC), the most widely used method for analyzing complex gas mixtures. Typical GC microcolumns are made through a multi-step fabrication process, which requires hazardous reagents, complex equipment, and problematic stationary phase coating procedures. This section of the thesis explores, as an alternative: a microcolumn made from a single microtextured polymer composite that acts as both the structural support and stationary phase. This work marks the first molded gas chromatography microcolumn capable of separating mixtures of VOCs in minutes with baseline resolution (N > 1800 plates m-1) and contributes significantly to understanding which factors (e.g., polymer permeability, phase-separated structure) must be considered in the design of such microcolumns. Finally, this work also describes advancements in realizing colorimetric sensor arrays as microdetectors for gas chromatography. Because GC miniaturization necessitates extremely short columns (often < 3 m in total length), micro-GC systems suffer from incomplete separations and frequently have analytes which coelute. Sensor arrays have been proposed as microdetectors for micro-GC analysis in an attempt to ameliorate this problem. Described here are initial studies on optimization of colorimetric sensor arrays for use with GC including the development of a solvatochromic array for sensing organic solvents, an analysis of the effects of secondary factors on sensor array kinetics, and a proof of concept study sensing amines as they elute from a microcolumn. These advances provide a basis for further development of colorimetric sensor array microdetectors for use with GC.
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Silicone microspheres and disposable separation technology for gaseous analytes
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