Quantitative investigation of convective flows in drying polymer films using 3D micro particle tracking velocimetry

液体加工的聚合物薄膜是许多创新产品的重要组成部分。突出的例子是清漆、光学薄膜、有机发光二极管或印刷的生物传感器。这种膜的干燥通常导致不希望的层厚度不均匀性和自由表面的变形，这对产品的质量具有相当大的影响。这些效应可以归因于表面张力驱动的对流流动，即所谓的马兰戈尼对流，其由局部不均匀的溶剂蒸发引起。为了提高表面质量，必须避免或至少减少这些流动。为了研究这一现象，不仅要分析自由表面的变形，而且要了解在此过程中膜中的流动情况。在几个非常好的研究项目中，已经开发了用于描述热诱导对流的解析解和数值模拟。然而，在薄膜干燥的背景下，发生了迄今为止尚未成为研究工作的主题的其他现象。除了温度影响之外，溶剂含量在干燥期间连续降低，这另外影响表面张力梯度和对流的形成，并导致已经变形的膜表面的固化。在干燥过程中必须同时考虑这些耦合现象。据我们所知，没有相关的工作已经发表在这个问题上的literation.With拟议的研究项目，我们的目标是关闭这个差距的实验，定量调查溶质Marangoni流诱导的浓度梯度，使用3D微粒子跟踪测速。此外，确定相应的稳定性极限将有助于在这一领域的研究知识的显着增益。

Thin, liquid-processed polymer films are an important component of many innovative products. Prominent examples are varnishes, optical films, organic light-emitting diodes or printed biosensors. The drying of such films often leads to unwanted layer thickness inhomogeneity and a deformation of the free surface, which has a considerable influence on the quality of the products. These effects can be attributed to surface-tension driven convective flow, so-called Marangoni convection, which is induced by locally inhomogeneous solvent evaporation. To increase the surface quality, it is necessary to avoid or at least reduce these flows. In order to investigate this phenomenon, not only an analysis of the deformations of the free surface, but also the knowledge of the flows in the film during the process is essential. In several very good research projects, analytical solutions and numerical simulations for the description of thermally induced convection have already been developed. In the context of film drying, however, other phenomena occur which have not been subject of research efforts so far. In addition to temperature effects, the solvent content decreases continuously during drying, which additionally influences the formation of surface tension gradients and convective flows and leads to a solidification of the already deformed film surface. These coupled phenomena have to be considered simultaneously during drying. To the best of our knowledge, no relevant work has been published on this subject in the literature.With the proposed research project, we aim to close this gap by experimental, quantitative investigations of solutal Marangoni flows induced by concentration gradients using 3D micro particle tracking velocimetry. In addition, the determination of corresponding stability limits will contribute to a significant gain of knowledge in this field of research.