Computational modelling for inkjet-printed electronics.

PEDOT是一种导电聚合物，在小型电子元件中显示出潜力。实验表明，PEDOT薄膜的电导率高达6300 S/厘米[Guye等人。2020]，仅比大多数导电金属小10倍。然而，这种导电性高度依赖于制备方法。在实验环境中，PEDOT首先以PEDOT：PSS络合物的形式引入，该络合物溶解在水-DMSO共溶剂混合物中，然后喷射到基质上。随着共溶剂的蒸发，一些PEDOT：PSS解离，留下含有富含PEDOT和PSS区域的残留物。为了获得最佳性能，这种残留物应该在富含PEDOT的部位之间表现出良好的互连性，并且应该具有接近均匀的厚度分布。因此，重要的是要充分了解溶剂挥发过程中各组分的动态。液滴蒸发的流体动力学对PEDOT沉积的形貌有很大的影响。因此，我们将研究蒸发诱导的静止液滴中的毛细管流，以及它们如何导致溶质颗粒的接触线聚集。在文献中，这是一种无处不在的现象，被称为“咖啡环效应”(CRE)，在大多数工业环境中都是不受欢迎的(包括这里概述的环境)。除了了解咖啡环的形成，我们还希望探索哪些可以通过实验获得的物理参数(环境温度、湿度、颗粒大小/形状等)。可以被利用来压制他们。这将包括在表面组装方面的一些新工作，这已经在高蒸发速率下得到了实验证明[Li 2016]，但缺乏一个数学框架来给出与实验数据一致的结果。由于跟踪堵塞粒子锋面的复杂性，许多现有的CRE模型仅限于轴对称几何形状。此外，由于干燥后期液滴表面的拓扑变化，这些模型无法捕捉到完整的蒸发过程。使用有限元库Oomph-lib[Heil，Hazel 2006]，我们将为CRE开发一个新的计算框架，以解决这两个问题。这一框架将使我们能够研究接触线曲率对局部CRE强度的影响，并将我们的模型应用于滴状构建的印刷线。分析和计算工作将与诺丁汉的添加制造中心(CfAM)的合作伙伴一起进行，在那里，量身定制的实验将使我们能够对结果进行基准测试，并深入了解如何在建模中捕捉相关物理因素。

PEDOT is an electrically-conductive polymer which shows potential for use in small-scale electronic components. Experimentally, thin films of PEDOT been shown to exhibit a conductivity of up to 6300 S/cm [Gueye et al. 2020], only a factor of 10 smaller than most conductive metals. This conductivity, however, is highly dependent on the method of preparation. In an experimental setting, PEDOT is first introduced in the form of the PEDOT:PSS complex, which is dissolved in a water-DMSO co-solvent mixture and then jetted onto a substrate. As the co-solvents evaporate, some of the PEDOT:PSS dissociates, leaving a residue containing both PEDOT-rich and PSS-rich regions. For optimal performance, this residue should exhibit good interconnectivity between the PEDOT-rich sites and should have a thickness profile which is close to uniform. It is therefore important that the dynamics of each constituent during solvent evaporation are well-understood. The fluid dynamics of drop evaporation has a strong influence in the morphology of the PEDOT deposit. Thus, we will examine the evaporation-induced capillary flows in an evaporating sessile droplet and how they lead to contact-line aggregation of solute particles. In the literature, this is a ubiquitous phenomenon known as the 'coffee ring effect' (CRE) and is undesirable in most industrial settings (including the one outlined here). In addition to understanding the formation of coffee rings, we hope to explore which experimentally accessible physical parameters (ambient temperature, humidity, particle size/shape etc.) can be exploited to suppress them. This will include some novel work in surface assembly, which has been demonstrated experimentally at high evaporation rates [Li 2016] but lacks a mathematical framework that gives results consistent with experimental data.Many existing CRE models are limited to axisymmetric geometries due to complications in tracking fronts of jammed particles. In addition, these models cannot capture the full evaporation process due to topological changes in the drop surface that arise in the late stages of drying. Using the finite element library Oomph-lib [Heil, Hazel 2006], we will develop a novel computational framework for CRE that remedies both these issues. This framework will allow us to study the influence of contact line curvature on the local CRE intensity and apply our model to printed lines which are built up dropwise.The analytical and computational work will be carried out alongside partners at the Centre for Additive Manufacturing (CfAM) in Nottingham, where tailored experiments will allow us to benchmark our results and give insight into how to capture the relevant physics in our modelling.