Investigation of interfacial instabilities with a two-layer slide coating process

Organic electronics have been thoroughly investigated due to their broad application potential, ranging from light-emitting diodes to photovoltaics. The processing of organic electronics is trending from vacuum toward wet chemical deposition, which allows fast low-cost mass production of devices with scalable dimension. One of the current challenges of wet film processing is the redissolution of already dried active materials when applying a liquid top layer. Further, increasing overall process efficiency by coating multiple liquid layers in one step raises such challenges as liquid–liquid mixing or dewetting. This article describes the experimental investigation of these instabilities for two-layer flows with organic solvents. A modified slide coating device was chosen where an extended plate after the slot exit allows prolonged observation of the flow while it travels down the plate. During experimentation, stable and unstable two-layer flows as well as different types of instabilities were detected. The key finding is a correlation of flow stability with the spreading coefficient, a combined measure of surface and interfacial tensions. Focusing on fluid properties, this paper succeeds in defining a three-dimensional stability window for a dual-layer flow.