Study and Stabilization of a Liquid Crystal Drop Formation Using a Piezoelectric Inkjet Printhead

Abstract

The development of inkjet printing processes is in great expansion for the fabrication of Microsystems thanks to less material waste and accurate dot placement. The quality of drop formation is known to depend on two main parameters: fluid viscosity and piezoactuator applied voltage. We are working with the thermotropic liquid crystal E7 which presents a nematic oriented phase for a temperature under 60°C and an isotropic phase above 60°C. Like other liquids, viscosity of thermotropic liquid crystals decreases with the temperature but presents a discontinuity at the phase transition, which can disturb the stability of drop ejection. Unfortunately, for the E7 liquid crystal, the piezoprinthead viscosity specifications (usually under 15cP) require a temperature increase close to the temperature transition. Thus, understanding the influence of phase transition on drop characteristics is crucial. Moreover, the applied voltage can be responsible for an electrical field perpendicular to the liquid movements, which can trouble the orientation of nematic phase molecules, change its apparent viscosity and alter the ejection process. In order to understand these phenomena, the influences of viscosity and applied voltage will be studied and discussed. An adjustment tool will be finally proposed to fit with experimental results and to reach finally stable formation of liquid crystal drops.