Graduate Thesis Or Dissertation
 

Electrospray Deposition of Discrete Nanoparticles: Studies on Pulsed-Field Electrospray and Analytical Applications

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9p290g61r

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  • Electrospinning and electrospray are both nano-scale material fabrication techniques, based on related phenomena of electrically charged fluid spray from a droplet of liquid. Material is dissolved in liquid, then a spray is generated by applying a high voltage, creating an electric field, between the fluid dispensing capillary and a grounded collection substrate. Nano-scale features of the dissolved material are collected when the solvent evaporates in flight between the needle and collection substrate. Though electrospinning and electrospray are terms that can be used interchangeably (they frequently are) electrospinning specifically refers to using the technique to generate nanofibers; electrospray is a more appropriate term for the spray of individual, charged droplets. Electrospray theory is also seen applied in electrospray ionization interfaces to mass spectrometers. The underlying principles of electrospray for mass spectrometry and electrospray for deposition are the same, but deposition targets a bulk coating of material instead of quantitative analysis of a small number of gas phase analytes. In this work, electrospray deposition of discrete features from individual, charged droplets was realized.There is some literature published on this topic, but electrospinning literature is overwhelmingly populated with work on the fabrication of continuous nanofibers and “beaded features” are typically considered as defects in desired morphologies. A significant portion of this work was in collaboration on a DARPA funded research project with a local industry sponsor. Due to compliance with non-disclosure, the exact motivation and specific applications to that project cannot be discussed in this thesis, although the premise can be addressed. The broad goal of the project was development of techniques and methodology for assembling structures comprising features spanning nano, micro and macro scale dimensions. On that project, electrospray was used to fabricate discrete nanoplate features on the order of 100-200nm in size. These features were deposited, using the electrospray technique, onto a branched architecture with dimensions on the micron length scale. Effort went toward controlling the size of these features through electrospray parameters and demonstrating the repeatability in deposition of these features onto the device architecture. Outside of the sponsored project work, generation of discrete nano-plate/particle features from protein and polymer materials was used in both direct applications and to investigate the impact of pulsed high voltage (or pulsed-field) on the electrospray process. The technique was used directly in two analytical chemistry applications: first, the deposition of blood coagulation chemistries onto a point-of-care-applicable blood plasma separation device, with the goal of improving its separative performance; and second, electrospray deposition of an enzyme on the working electrode in an electrochemical sensor application for glucose detection.Design, fabrication, and implementation of custom components was done using 3D printing, laser cutting, and CNC end-milling to facilitate both research toward the sponsored project and work discussed in this thesis. An acrylic enclosure was used for the depositions and saw several modifications to meet changing research needs. To study pulsed-field electrospray a transformer-based high voltage system was designed and assembled in-lab. This system had limitations but was applicable for generating high voltage pulse waveforms and was used to perform electrospray deposition research.
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