Browsing by Subject "Fabrication"

Now showing 1 - 5 of 5
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    Development, Characterization, and Applications of a 3D Printed micro Free-Flow Electrophoresis Device
    (2017-02) Anciaux, Sarah
    Micro free-flow electrophoresis (μFFE) is a unique separation technique because of its continuous nature. Analytes are pressure driven through a planar separation channel, and an electric field applied laterally to the flow producing a spatial separation. Fabrication methods associated with μFFE devices hinder our ability to address the limitations of μFFE. This work focuses on a novel fabrication method to reduce the overall fabrication cost and time, followed by validating and characterizing the device. A novel μFFE device is fabricated in acrylonitrile butadiene styrene (ABS) by 3D printing two sides of the device and then acetone vapor bonding them while simultaneously inserting electrodes and clarifying the device. Fluorescent dyes are separated, and their limit of detection determined. After validation of the new fabrication method, a new device design is made with the sample inlet modified so that 2D nLC × μFFE separations can be performed. 2D nLC × μFFE separations of fluorescent dyes, proteins, and tryptic BSA digest are demonstrated. These samples allow comparison between the surface properties of glass and 3D printed devices. Peak asymmetries, widths, and the interface were investigated. Minimal surface adsorption is observed for fluorescent dyes, proteins, and peptides, unlike in glass devices. After investigating surface properties, an open edge device for coupling to mass spectrometry is designed and compared to its glass counterpart. A novel ionization method is demonstrated from a hydrophobic membrane and the open edge device is shown to have stable flow.
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    Effect of Temperature on Prestressed Concrete Bridge Girder Strand Stress During Fabrication
    (Center for Transportation Studies, University of Minnesota, 2015-12) Swenson, Tanner W.; French, Catherine E. W.
    The Minnesota Department of Transportation has reported erection cambers of many prestressed concrete bridge girders that were much lower than anticipated. A previous University of Minnesota study (O’Neill and French, MnDOT 2012-16) attributed the discrepancies to inaccurate estimates of the concrete strength and stiffness at release and strand force loss due to temperature during fabrication. The objective of this study was to further investigate the effects of temperature on strand force and camber during precast, prestressed girder fabrication and to make recommendations for the design and fabrication processes to reduce the potential loss of prestress due to temperature effects during fabrication and to improve the release camber estimation. A thermal effects analysis was developed based on four key steps in the girder fabrication process: tensioning, concrete-steel bond, release, and normalization. The study included fabricating six short prestressed concrete segments released at early ages to determine the time/temperature associated with bonding the prestressing strand to the concrete. To investigate the non-recoverable prestress losses during girder fabrication, four sets of girders (MN54 and 82MW) were instrumented with thermocouples, strain gages, and in some cases load cells, that were monitored during the fabrication process to separate the thermal and mechanical strain components. Effects investigated included casting during a cold season, casting during a warm season, casting with the free length of strand covered, and casting with different bed occupancy during any season. A recommended procedure for adjusting strand force during tensioning was proposed to account for non-recoverable strand force changes due to temperature changes between tensioning and bond.
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    Electromechanical Switches Fabricated by Electrophoretic Deposition of Single Wall Carbon Nanotube Films
    (2015-08) Lim, Jun Young
    Power dissipation is a critical problem of CMOS devices especially for mobile applications. Many efforts have been made to solve the problem, but there are still major issues associated with scaling the device size. Micro electromechanical (MEMS) and nano electromechanical (NEMS) devices are one candidate to solve the problems because of their excellent standby leakage. However, the switches have a tradeoff between low operating power and high device speed. Suspended beams with low mass density and good mechanical properties provide a way to optimize the device. Carbon nanotubes (CNTs) have the low mass density and excellent mechanical properties to enable high performance MEMS/NEMS devices. However, the high temperature required for the direct synthesis for CNTs makes it difficult for them to be compatible with a substrate containing transistors. Therefore, continuous film deposition techniques are investigated with low temperature (< 300 C). Electrophoretic deposition (EPD) is a simple and versatile processing method to deposit carbon nanotubes on the substrate at room temperature. The movement of the charged CNTs in suspension occurs by an applied electric field. The deposited CNT film thickness can be controlled through the applied voltage and process time. We demonstrate the use of an EPD process to deposit various thicknesses of CNT films. Film thicknesses are studied as a function of, deposition time, electric field strength, and suspension concentration. The deposition mechanism of the EPD process for carbon nanotube layers was explained with experimental data. We determined the film mass density and electrical/optical properties of SWCNT films. Rutherford backscattering spectroscopy was used to determine the film mass density. Films created in this manner had a mass density that varies with thickness from 0.12 to 0.54 g/cm3 and a resistivity of 2.1410-3 Ω∙cm. For the mechanical property measurements, we describe a technique to fabricate free-standing thin films using modified Langmuir-Blodgett method. Then we extracted the Young’s modulus of the film from the load-displacement data from nanoindentation using the appropriate modeling. The Young’s modulus had a range of 4.72 to 5.67 GPa, independent of deposited thickness. We fabricated two-terminal fixed beam switches with SWCNT thin films using the EPD process. Device pull-in voltages under 1V were achieved by decreasing the air-gap. The pull-in voltages were compared with the calculated results using the device geometry and extracted Young’s modulus from nanoindentation. Generally good agreement was observed. Also, we found a range of 2.4 to 3.5 MHz resonant frequency. However, we encountered several problems with the device including a gradual turn-on, hysteresis between pull-in and pull-out voltage, changes in the pull-in voltages with repeated on-off cycling, and early failure due to moisture absorption during testing in the air. Mechanisms for these observations are postulated. Further work is needed to improve device performance and reliability.
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    Enhancing Micro Free Flow Electrophoresis: Detection, Application, And Fabrication
    (2023-04) LeMon, Matthew
    Micro Free Flow Electrophoresis (µFFE) is a separation technique where analytes are moved through a planar separation channel via pressure driven flow. Analytes streams are deflected laterally within an electric field applied perpendicular to the flow and separated from one another based on differences in their electrophoretic mobility. Notably, µFFE is capable of continuously separating analytes making it uniquely useful for a range of applications such as multidimensional separations, microscale sample purification, and continuous on-line monitoring. This work focuses on improving the sensitivity of laser induced fluorescence (LIF) detection via modifying the laser alignment, exploring new device designs for rapid on-line buffer exchange, and developing a novel fabrication technique for hot embossing µFFE devices in cyclic olefin copolymer (COC) with the goal of expanding µFFE’s use in analytical workflows. A new laser alignment for LIF was explored, focusing the laser light through the side of the device instead of spreading it into a line and reflecting it down onto it. Improvement in the limit of detection (LOD) for fluorescein was obtained in a glass µFFE device using this alignment; however, it was found to be incompatible with 3D printed acrylonitrile butadiene styrene (ABS) due to excessive scattering of the laser light. New µFFE device designs were developed and modeled using Multiphysics modeling software to optimize a design for rapid on-line buffer exchange. This was performed with the intent of interfacing incompatible separation modes with electrospray ionization mass spectrometry (ESI-MS) to develop novel multi-attribute analysis techniques for the assessment of therapeutic monoclonal antibodies (mAbs). Lastly, a novel fabrication technique for µFFE was developed to hot emboss µFFE devices in COC utilizing a poly jet 3D printed master mold. The performance of devices produced this way were tested via a separation of three fluorescent dyes. Their LODs quantified and compared to similar ABS and glass µFFE devices.
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    Instrumentation and Fabrication of Two High-Strength Concrete Prestressed Bridge Girders
    (Minnesota Department of Transportation, 1998-01) Kielb, Jeffrey; French, Catherine E.; Leon, Roberto T.; Shield, Carol K.
    This report describes the design, instrumentation, construction, and test set-up of two high-strength concrete prestressed bridge girders. The girder specimens were constructed to evaluate prestress transfer length, prestress losses, flexural fatigue, ultimate flexural strength, and ultimate shear strength. Each test girder was a 132.75-foot long, 46-inch deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with 46 0.6-inch diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi. Each girder was made composite with a 9-inch thick, 48-inch wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi. Girder I used a concrete mix incorporating crushed limestone aggregate while Girder II utilized round glacial gravel aggregate in the mix with the addition of microsilica. In addition, the two test girders incorporated two different end patterns of prestressing--draping versus a combination of draping and debonding--and two different stirrup configurations--standard Mn/DOT U versus a modified U with leg extensions. More than 200 strain gages were imbedded in each girder during construction. Other reports present flexural and shear testing results.