Pattern formation in slot-die coating

Abstract

We experimentally study the occurrence of pattern formation during the slot-die coating of partially wetting liquids onto polyethylenterephthalat-substrates outside the coating window. The experimental investigation is supported by numerical simulations of a dynamical model. Our results demonstrate that beyond a critical coating speed, the deposition of homogeneous coating layers undergoes an instability resulting in the self-organized emergence of patterned coatings, i.e., stripes of different orientation and droplet patterns. We investigate the transitions between the different patterns as triggered by changes in the control parameters inherent to slot-die coating, e.g., the liquid viscosity and the coating gap height. The relatively simple theoretical approach is based on lubrication theory. It is already able to reproduce most of the patterns observed experimentally and reveals a wettability-driven instability mechanism.