Conductive Materials for Additive Manufacturing: Towards Multi-Functional, Multi-Material 3D Printed Systems
- Elwood, Jacqueline
- Advisor(s): Lin, Liwei
Abstract
Additive manufacturing or three-dimensional (3D) printing has been popularized in applications, including automotive, aerospace, medical, architectural, consumer products, and electronics. Despite interest in using 3D printing for microdevice fabrication, limitations in resolution, surface roughness, support material removal, dimensional fidelity, and material diversity have limited the scope of applications. 3D printing techniques are generally limited to a single class of material due to incompatible processing requirements between multiple types of materials, which limits the electrical functionality, mechanical properties or other functionalities of one or more materials. This dissertation presents methods combining mechanically and electronically functional materials, resulting in a new class of multi-functional, multi-material 3D printed systems to address the limitations of current single-material 3D printing systems.
For commercial 3D printing systems that utilize proprietary materials, where the surface chemistry is relatively unknown, there are few viable options to construct electrical materials. In the first part of this dissertation, the commercially available, intrinsically conductive polymer PEDOT:PSS has been modified to chemically adhere to MultiJet 3D printing materials, where their exact compositions are unknown. A study into the addition of silane to enhance adhesion of PEDOT:PSS chains to a polymer surface is conducted and the conductivity of the PEDOT:PSS film is further enhanced by the introduction of other additives into the polymer mixture. A three-dimensional lattice structure is printed and coated with this polymer mixture to generate a 3D electrode structure. As a demonstration example, a prototype sensor capable of determining changes in ethanol content in water has been tested via changes in conductivity with a measured detection limit of ~0.19 %v/v.
The second part of this dissertation proposes a method for fully-3D printed multi-material structures using stereolithography 3D printing. A mixture of Ni particles and commercially available 3D printing resin is created to realize an electrically functional material that can be printed using a benchtop stereolithography 3D printer. A printing protocol is developed to enable the generation of multi-material structures with a single 3D printer and the conductivity of the Ni-resin composite part is measured to be ~150 S/cm. With the ability to print multi-functional, multi-material systems, a microfluidic capacitive sensing device is proposed to demonstrate the potential application of this printing technique.