Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Aaron D. Price

Abstract

Conjugated polymers (CPs) are a class of polymers that exhibit a change in size or shape in response to electrical stimuli. The unique combination of electrical and mechanical properties facilitates the fabrication of novel devices in a broad range of applications including: sensors, actuators, and lab-on-a-chip systems. The alternating single and double bonds along the polymer chain of CPs enables their electroactive properties but is also responsible for processability associated with CPs that has limited fabrication methods. Recently a photosensitive CP composite enabling additive manufacturing (AM) of 3D CP structures was developed. However, the introduction of a copolymer for mechanical stability resulted in a commensurate loss in electroactive performance, and this loss needs to be addressed to unlock to potential of 3D CP devices. This work has identified two main themes for the advancement of 3D CP devices. First, improvement of AM approaches for 3D CP devices is conducted through the development of extrusion-based direct ink writing (DIW) of passive support structures as well as the further development of existing photosensitive CP resin formulations for use in vat polymerization of 3D CP-composite structures. Secondly, the improvement of electroactive performance of 3D CP-composite devices is explored through methods to increase surface area and reduce diffusion path lengths by the deposition of hierarchical CP structures. Development of a DIW process leveraging a support gel improved resolution and quality of 3D polydimethylsiloxane (PDMS) structures enabling the fabrication of 3D CP bilayer devices. The DIW process has also been paired with the development of a PDMS-carbon nanotube composite to produce 3D tubular strain sensors for applications in fluidic networks. The electrical conductivity of CP photosensitive resin formulations has been improved through the integration of polypyrrole (PPy) functionalized carbon nanotubes. This improvement to the material properties enabled the development of a soft-template polymerization process to deposit hierarchical PPy structures on vat polymerized CP composite films. Films with hierarchical PPy features demonstrated improved electroactive performance compared to those deposited with conventional 2D PPy films. Development of these fabrication methods and improved material properties further advances the potential of 3D CP devices and bridges the gap between the micro- and nanoscales towards controllable nanoscale CP features.

Summary for Lay Audience

Conjugated polymers (CPs) are a class of polymers that exhibit a change in size or shape, in response to electrical input. The unique combination of electrical and mechanical properties facilitates the fabrication of novel devices in a broad range of applications including: sensors, actuators, and lab-on-a-chip systems. The alternating single and double bonds along the polymer chain of CPs enables their electroactive properties but is also responsible for processability associated with CPs that has limited fabrication methods. Recent work in the Organic Mechatronics and Smart Materials Laboratory developed a light-sensitive CP composite enabling additive manufacturing (AM) of 3D CP structures. However, the introduction of a secondary material for mechanical stability resulted in a loss in electroactive performance limiting potential applications. This work has identified two main themes for the advancement of 3D CP devices. First, improvement of AM approaches for 3D CP devices is conducted through the development of extrusion-based direct ink writing (DIW) of passive support structures as well as the further development of existing light-sensitive CP material compositions for use in vat polymerization of 3D CP-composite structures. Secondly, the improvement of electroactive performance of 3D CP-composite devices is explored through methods to increase surface area and reduce minimum feature size by the deposition of hierarchical CP structures. Development of a DIW process using a support gel improved resolution and quality of 3D polydimethylsiloxane (PDMS) structures enabling the fabrication of 3D CP bilayer devices. The DIW process has also been paired with the development of a PDMS-carbon nanotube composite to produce 3D tubular strain sensors for applications in fluidic systems. The electrical conductivity of CP photosensitive resin formulations has been improved through the integration of polypyrrole (PPy) functionalized carbon nanotubes. This improvement to the material properties enabled the development of a soft-template polymerization process to deposit hierarchical PPy structures on vat polymerized CP composite films. Films with hierarchical PPy features demonstrated improved electroactive performance compared to those deposited with conventional 2D PPy films. Development of these fabrication methods and improved material properties further advances the potential of 3D CP devices and bridges the gap between the micro- and nanoscales towards controllable nanoscale CP features.

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