Spread and retraction dynamics of droplet coalescence on a rectangular pixel for organic light-emitting diode inkjet printing

Abstract

In organic light-emitting diodes (OLEDs) manufacturing, inkjet printing has rapidly become popular due to its high resolution and low cost. However, the mechanism of droplet impacting on a rectangular pixel in OLEDs inkjet printing is not yet clear. In this paper, coalescence dynamics of droplet impacting on a rectangular pixel including the spread and retraction stages is simulated by the software of fluent. In addition, a dynamic model is proposed to analyze the spread and retraction behavior of droplet impacting on a rectangular pixel. In the spread stage, the dynamic equation of spread length with respect to time is derived based on energy and mass conservation. In the retraction stage, the variational principle instead of solving the complete Navier–Stokes equation is used to simplify the calculation. On this basis, the dynamic equation of retraction length with respect to time is achieved, and the theoretical solution is in agreement with the numerical result. Finally, the influences of droplet offset, size, and initial velocity on coalescence dynamics are analyzed. Furthermore, the dynamic model proposed in this paper provides a new possibility for the coalescence of a droplet impacting on a heteromorphic microcavity instead of a flat substrate.