Effect of hydrophobic/hydrophilic tendencies on inkjet printing for wearable electronics

Abstract

Inkjet printing is a method used to precisely deposit ink drops onto substrates. This method can be used in the creation of wearable electronics for health monitoring and biosensing. Inkjet printed ultrathin, flexible, and stretchable electrodes can form intimate integration with the skin for high quality biopotential signal acquisition and help with the comfort of the wearer. However, we must understand the solid-liquid interaction and ink wettability before continuing further into the inkjet printing process. Therefore, studying the hydrophobic/hydrophilic tendencies is important to further our understanding of what we can accomplish within the field of inkjet printing. By using the March Juniper III Reactive Ion Etcher, the surfaces of sample plates were treated with oxygen gas (O2) and carbon tetrafluoride (CF4) in a vacuum chamber. After treatment, a bead of water was used to view the hydrophobicity of the treated surface, and a photo was taken using a DinoCapture 2.0 camera. By using various treatments of O2 and CF4, contact angles can be measured and compared to one another. Our results show that after the initial treatment of O2, the surface becomes hydrophilic. By adding CF4, the surface becomes more hydrophobic the longer the treatment takes. These conditions can be used further to create a specific angle measurement when printing an electrode.