Additive Manufacturing of Conducting Polymers

Abstract
   Conducting polymers (CPs) are widely used in applications including wearable electronics and on-skin biosensors, which can benefit from custom 3D topographies via additive manufacturing (AM), also known as 3D printing. However, processing sensitivities of CPs render the combination of structural complexity and high electrical conductivity difficult to achieve. My PhD work focuses on overcoming these challenges. We first took advantage of CPs’ solution processability and used direct ink write (DIW) to print a custom poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) ink with moderate conductivity and high anisotropy. Complementary characterizations revealed that the anisotropic conductivity was a result of the phase separation between PEDOT and PSS. Removal of the PSS shells reduced anisotropy and led to a significant increase in conductivity to over 1200 S/cm. However, the DIW mechanism limits the structural complexity of printed objects, prompting us to develop a 3D printing-assisted casting method to balance shape complexity and high conductivity. We first developed a new vat-photopolymerization method to print 3D molds with complex geometry, including octet and truncated octahedron lattices. We then explored a unique solid-state reaction of PEDOT by melt-processing a precursor into the molds. Mold removal followed by mild heating led to PEDOT monolith with excellent shape-retention. 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 improved the understanding of processing-structure-property relationships of 3D printed CPs and yielded new methods for additively-manufacturing these chemically temperamental materials, opening doors to new applications.
   

Biography
   Ian Hill is a PhD candidate in Materials and Biomaterials Science and Engineering at the University of California, Merced. He earned his B.S. in Biological Sciences with a minor in Chemistry from California State University, Stanislaus. His research interests include organic and polymer synthesis, structure-property relationship investigation, and additive manufacturing. The main focus of his Ph.D. work has been to developing new strategies for the additive manufacturing of conducting polymers while improving their electrical performance. He was awarded the UC Merced Graduate Dean’s Dissertation Fellowship for his research.