Coalescence Dynamics of a Droplet Impacting on a Rectangular Pixel for Inkjet Printing

A droplet impacting on a rectangular pixel with an offset is prone to cause the liquid to spread out of the pixel and adhere to adjacent pixels in organic light-emitting diode (OLED) inkjet printing. Therefore, the coalescence of a droplet impacting on a rectangular pixel is crucial in understanding the reliable OLED inkjet printing. In this paper, an assumption is established that the rectangular coalescence process is divided into the fusion part and spread part. On this basis, a dynamics model is introduced to analyze the coalescence behavior of a droplet impacting on a rectangular pixel. According to the law of conservation of mass and energy, dynamic equations are developed to obtain the maximum spread length as a function of time. In addition, the volume of the fluid method is used to simulate coalescence dynamics of a droplet impacting on a rectangular pixel by using the software of FLUENT, and the analytical solutions are consistent with the simulation results. Furthermore, the effects of the positioning error and initial velocity on the coalescence dynamics are analyzed. The results show that small initial velocity and positioning error of the droplet are helpful for the reliable OLED inkjet printing.