UC Merced

Conducting polymers (CPs) are widely used in applications including wearable electronics, on-skin biosensors, and tissue engineering, all of which can benefit from custom 3D topographies via additive manufacturing (AM), also known as 3D printing. However, the environmental and processing sensitivities of CPs render the combination of structural complexity and high electrical conductivity difficult to achieve. In this dissertation, I will discuss the strategies developed through my PhD work that have overcome some of these challenges. First, by taking advantage of the solution processability of CPs, we employed direct ink write (DIW) to print a custom poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) ink. The printed specimens exhibit moderate conductivity and high anisotropy. A variety of complementary characterizations revealed that the anisotropic conductivity is a result of the phase separation between PEDOT and PSS. Removal of the PSS shell has reduced anisotropy and led to a significant increase of conductivity to over 1200 S/cm. However, the structural complexity of the resulting prints is low due to the intrinsic limitations of the DIW technique, prompting us to explore a two-step vat-polymerization method to first 3D print the dopant network followed by infiltrating CPs through interfacial polymerization. Excellent geometric complexity has been achieved; however, the conductivity is unsatisfactory (<0.1 S/cm) due to the high dopant polymer concentration. Finally, we developed a 3D printing-assisted casting method to balance shape complexity and high conductivity. A PEDOT precursor is melt-processed into vat-photopolymerized 3D molds. Upon mold removal, the precursor is polymerized into PEDOT in the solid-state with excellent shape-retention. Complex objects such as octet, truncated octahedron, and trees have been achieved. Their electrical conductivity can be made as high as 7000 S/cm by compositing the molten precursor with silver flakes. Collectively, this body of work has led to an improved understanding of processing-structure-property relationships of 3D printed conducting polymers as well as new methods for additively manufacturing these chemically temperamental electronic materials, opening doors to new applications.