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Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2019

Month Degree Awarded

February

First Advisor

James J. Watkins

Second Advisor

Sarah L. Perry

Third Advisor

Kenneth R. Carter

Subject Categories

Electronic Devices and Semiconductor Manufacturing | Nanotechnology Fabrication | Other Analytical, Diagnostic and Therapeutic Techniques and Equipment | Polymer and Organic Materials | Polymer Science | Semiconductor and Optical Materials

Abstract

This dissertation examines the direct printing of conductive inks on polymeric substrates for applications in organic electronics, microfluidic valving systems, and wearable sweat sensors. The inexpensive production of solution-based electrodes with high electrical conductivity is necessary to enable the next-generation of printed, flexible, and organic electronics. Specifically, the optimization and printing of liquid-phase graphene ink and nanoparticle-based silver ink by soft nanoimprint lithography and inkjet-printing is discussed to achieve printed functional devices. Using scalable low-cost patterning systems, these flexible applications are compatible with roll-to-roll processing, enabling large-scale manufacturing. This research expands the knowledge of high-resolution printing optimization for the direct patterning of organic electronics and development of sweat-based microfluidics for point-of-care diagnostic devices.

Chapter 1 describes the introduction of liquid bridge-mediated transfer printing of graphene ink for customizable electrodes and interconnects. Flexible, printed, and organic electronics are hindered by low transistor integration density due inherent size resolutions of traditional printing technology. In comparison, soft nanoimprint lithography-based methods offer an alternative high-throughput method and roll-to-roll compatible patterning of electrodes. Graphene ink is directly printed using an ethanol liquid bridge to produce uniform and precise electrodes, squares, dots, and line arrays on a variety of substrates, illustrating the versatility of transfer printing. Furthermore, single-crystal transistors were fabricated using printed graphene electrodes with both n-type and p-type semiconductors, revealing excellent transfer and output characteristics in ambient conditions. Organic inverters were also produced by integration of n-type and p-type devices, demonstrating high gain values and symmetric switching. This work extends the high-resolution applications of solution-based graphene ink for the field of organic printed electronics.

The second chapter focuses on the development of robust electrowetting valves for sweat-based wearable microfluidic devices. Despite important advances in wearable sweat sensors, there are few reports regarding the integration of valving mechanisms into these devices. This incorporation of microfluidic valves for time-stamped sweat collection or multiple reagent reservoirs would enable the capability of complex analysis for improved personal health monitoring. Electrowetting valves offer compelling opportunities for portable, disposable, low-cost, and flexible valving systems with low power requirements for actuation. The fabrication and assessment of wearable electrowetting valves using a hydrophilic substrate for capillary-driven flow and medical-grade skin adhesive for conformal body contact is introduced. Moreover, these electrowetting valves for sweat-based microfluidics outperformed the electrowetting valves discussed in previous literature in terms of valve hold time and electrode spacing. These solution-based and low voltage valves broaden the applications of electrowetting valves for point-of-care diagnostics in the area of noninvasive personal sweat monitoring.

Finally, Chapter 3 evaluates the performance of a microfluidic sweat sensing platform developed using scalable printed electronics and low-cost adhesive-based microfluidics. Sweat contains valuable information regarding electrolytes, amino acids, small molecules, and proteins levels within the body. Harnessed as a diagnostic tool, sweat would enable individuals to gain a deeper understanding of overall health status through personalized and wearable monitoring. Specifically, an inexpensive skin-compatible microfluidic platform is developed for continuous glucose monitoring through sweat. Solution-based electrochemical sensor electrodes are optimized for inkjet-printing and electrodeposition conditions. Additionally, an elastomeric polymer skin is fabricated, imitating human eccrine sweat gland size and distribution. This synthetic skin is integrated with the microfluidic glucose sensor to deliver artificial perspiration through the device at physiologically relevant sweating flow rates. Lastly, the sensor performance demonstrated glucose detection at levels measureable in human sweat for diabetic patients.

Available for download on Saturday, February 01, 2020

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