Three-dimensional printing of conductive composite for wireless chemical sensor systems

Three-dimensional (3D) printing technologies were developed in a variety of processes and applied in various fields such as manufacturing, healthcare, construction, etc. The extrusion-based 3D printing is one of the major 3D printing technologies which usually uses filaments or ink materials. Viscous liquid type ink materials may include polymer matrix and filler materials which are optimized to formulate the ink with the required printability with shear thinning behavior and functionality based on electrical conductivity or dielectric properties. The property of prints will largely depend on the choices of the polymer matrix and filler materials as well as types of printing technologies. The objective of this study is to understand the electrical properties of prints depending on printing parameters such as nozzle shapes and interaction between polymer matrix and fillers. The cross-sectional shapes of nozzles determine the flow of matrix material and fillers and affect the orientation of conductive fillers with a high aspect ratio like silver nanowires (AgNWs) in prints, which has a close relationship with the conductivity of prints. Matrix materials also play a significant role for the orientation of fillers in prints. Rod-like CNCs work like a media for AgNWs to move or rotate freely in it. In contrast, CNFs have shapes like spaghetti noodles which prevent AgNWs from moving or rotating in the matrix. A wireless electro-chemical sensing platform was developed by using 3D printable conductive cellulose composite. An inductor and capacitor (LC) resonator was prepared from a conductive nanocellulose ink by extrusion 3D printing for RF wireless chemical sensing. This LC resonator printed by direct ink writing with AgNW-CNF ink material was connected to an ion selective membrane electrode (ISME) to make a wireless sensor system which is a series connection of an LC resonator and an ISME. This wireless ISME-LC sensor was demonstrated with high selectivity and sensitivity of detection. This thesis demonstrated wireless ion-selective sensing using RF communication. To our best knowledge, this is the first thesis which report on wireless detection of selective ions from an ISME integrated with a wireless LC circuit. As an application of wireless sensing platform, wireless chemical sensing robot was developed by 3D printing using eco-friendly conductive composites based on nanocellulose. The aforementioned ISME-LC sensor was embedded on the tip of humanoid robotic fingers which actuated by quantitative chemical sensing of primary ions and demonstrated with an intelligent sensing robot. It is expected that this disposable wireless sensing robot system composed of simple ISME and LC will open an innovative way to contribute in the various sensing robot applications.