Evaporation of Pinned Droplets Containing Polymer – An Examination of the Important Groups Controlling Final Shape

Controlling the final shape resulting from evaporation of pinned droplets containing polymer, is important in the fabrication of P-OLED displays by inkjet printing. Typically, a coffee ring shape arises, due to the pinning and associated outward capillary flow. For operational reasons, this is undesirable – a flat topography is required. The aim of this work is to understand the important groups governing the shape, to provide a practical guide to ink selection. The theory presented is based on a thin-film lubrication model. The governing equations are solved numerically and continuously track the lateral progression of a liquid/gel front. A large capillary number or large ratio of initial to maximal polymer volume fraction can suppress the coffee-ring. White light interferometry is used to confirm these findings experimentally. VC 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 1759–1767, 2015