Critical Solutal Marangoni Number Correlation for Short-Scale Convective Instabilities in Drying Poly(vinyl acetate)-Methanol Thin Films.

Max Tönsmann,Wilhelm Schabel,Philip Scharfer

doi:10.3390/polym13172955

Abstract

A new empiric correlation for the critical solutal Marangoni number as function of the Péclet and Schmidt numbers is proposed. It is based on previously published experimental flow field data in drying poly(vinyl acetate)-methanol films with an initial thickness in the range of – and an initial solvent load of to , as well as newly derived concentration profile measurements and 1D drying simulations. The analysis accounts for realistic transient material properties and describes the occurrence of short-scale convective Marangoni (in)stabilities during the entire drying process with an accuracy of 9%. In addition, the proposed correlation qualitatively follows trends known from theory. As convective Marangoni instabilities in drying polymer films may induce surface deformations, which persist in the dry film, the correlation may facilitate future process design for either thin films with uniform thickness or deliberate self-assembly.

Highlights

Thin functional polymer films are used in many products, such as displays, organic light emitting diodes, biosensors, battery separators, or membranes for fuel cells
Since polymer films are commonly produced from solvent solution via coating and subsequent film drying, convective instabilities in the drying liquid film have the potential to induce free-surface deformations which persist in the dry polymer films [3]
The results are structured as follows: Initially, the vertical concentration profiles from 1D drying simulations are validated with Inverse Micro Raman Spectroscopy (IMRS) experiments (Section 3.1)

Summary

Introduction

Thin functional polymer films are used in many products, such as displays, organic light emitting diodes, biosensors, battery separators, or membranes for fuel cells. In order to ensure product functionality and high efficiencies, film thickness variations should not exceed 1% in many applications [1,2]. Since polymer films are commonly produced from solvent solution via coating and subsequent film drying, convective instabilities in the drying liquid film have the potential to induce free-surface deformations which persist in the dry polymer films [3]. A fundamental knowledge regarding the impact of drying conditions on convective instabilities is desirable. One-Dimensional Polymer Film Drying with regard to jurisdictional claims in

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Conclusion