| This thesis describes the development of a new ink jet technology—electrohydrodynamic printing, which offers a direct and flexible approach for high resolution patterning. The methodology involves producing a thin, intact jet by electric field and ‘writing’ with the jet on substrates to produce complex patterns. Three main issues of the printing process are addressed: (i) the formation of an electrically driven jet, (ii) the deployment of the jet to a substrate, and (iii) the ordering of particles in the printed features.; The first issue focuses on the investigation of the cone jet transition, a phenomenon employed to provide a large ‘neck-down’ ratio between the diameters of nozzle and the electrically driven jet. This helps reduce the inherent clogging problems in small channels. The scaling laws of the cone jet transition were studied and tested experimentally. In the course of study, a new operating regime of the cone jet transition is discovered where current varies inversely with flow rate. A mechanistic model based on electrochemistry at the orifice is proposed and qualitatively explains the inverse dependence.; The second issue explores the steady deployment of an intact, charged jet on the substrate. Specifically, the capillary break-up and the whipping of the electrified jet are eliminated by adjusting the electrical conductivity and viscosity of the liquid. Further, a nozzle-ring printhead configuration is designed to improve the deployment accuracy by ‘electrostatically focusing’ jets in the center, and the substrate movement is matched to the jet speed to reduce local spreading due to buckling at the impact point.; Finally, direct printing of colloidal crystal line of a few microns wide is demonstrated with electrohydrodynamic printing. A new way of manipulating particle arrangement in the printed line is discovered, which employs a contact-line-driven colloidal crystallization process to assemble particles into compact arrays. The process is analyzed by balancing the capillary interaction between partially immersed particles with the frictional force between particles and the substrate. The analysis indicates the existence of a critical particle-diameter-to-line-width ratio that determines the transition of morphology of a dried colloidal line from a double-stripe pattern to a single crystalline line. |
