Lattice Boltzmann Study of Microdroplet Evaporation Process in Pixel Pits

Inkjet printing has the advantages of high material utilization,low cost, and large-area production and is a promising manufacturingtechnology for organic light-emitting diode (OLED) displays. However,the droplet evaporation in micron-size pixel pits is highly influencedby the pit wall. Such a process is extremely difficult to control,leading to the appearance of defects such as the coffee ring in theprinting process of OLED displays. In this work, a multiphase thermallattice Boltzmann (LB) model based on multiple distribution functionsis established to study the evaporation process of micron-size dropletsin pits. According to the characteristics of the largest number ofthe three-phase contact line (TCL) appearing in the evaporation process,the evaporation modes can be divided into three types, i.e., one,two, and three TCLs. In the 1-TCL mode, the droplet stays in constantcontact radius (CCR) for the shortest time; in 2-TCL and 3-TCL modes,the liquid film fracture behavior of evaporating droplets in the pitis well captured. The effects of the pit height and the contact angleon the droplet evaporation mode are investigated in detail. The phasediagrams of evaporation modes with different parameters are also established.The revealed evaporation mechanism is supposed to be useful for regulatingthe droplet evaporation behavior and controlling the cured film shapein the OLED printing process.

Automated summary

Inkjet printing is a promising manufacturing technology for OLED displays due to its high material utilization, low cost, and large-area production advantages. However, the evaporation of droplets in micron-size pixel pits is difficult to control, leading to defects like the coffee ring. This study establishes a multiphase thermal lattice Boltzmann (LB) model to investigate the evaporation process of droplets in pits and explores the effects of pit height and contact angle on the evaporation mode. The revealed evaporation mechanism can help regulate droplet behavior and control the cured film shape in the OLED printing process.