Abstract
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. © 2015 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 61: 1759–1767, 2015
Highlights
There are a vast number of systems for which evaporation of a droplet, containing a nonvolatile component is relevant
This article presents an analysis of the important groups that control the final shape of a volatile, pinned droplet, containing polymer
The outward capillary flow, transports polymer to the edge, where it is deposited in a ring shape
Summary
There are a vast number of systems for which evaporation of a droplet, containing a nonvolatile component is relevant. Unlike existing display technologies, such as Liquid Crystal Displays (LCDs), they do not require a backlight with filters and they can be fabricated using a flexible and extremely thin substrate, rather than an inflexible layer of glass. For these reasons, they have the potential for much larger viewing angles and for use in the generation of flexible electronics applications, such as curved television displays
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