Computational modelling for inkjet-printed electronics.

PEDOT是一种导电聚合物，显示出在小规模电子元件中使用的潜力。实验表明，PEDOT薄膜的电导率高达6300 S/cm [Gueye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。在实验设置中，首先以PEDOT：PSS络合物的形式引入PEDOT，将其溶解在水-DMSO共溶剂混合物中，然后喷射到基底上。随着共溶剂蒸发，一些PEDOT：PSS解离，留下含有富含PEDOT和富含PSS区域的残余物。为了获得最佳性能，该残留物应在富含PEDOT的位点之间表现出良好的互连性，并应具有接近均匀的厚度分布。因此，很好地理解溶剂蒸发过程中每种成分的动力学是很重要的。液滴蒸发的流体动力学对PEDOT存款的形态有很强的影响。因此，我们将研究在蒸发固着液滴中蒸发诱导的毛细流动以及它们如何导致溶质颗粒的接触线聚集。在文献中，这是一种普遍存在的现象，称为“咖啡环效应”（CRE），在大多数工业环境中（包括本文概述的环境）都是不可取的。除了了解咖啡环的形成，我们还希望探索哪些实验上可获得的物理参数（环境温度，湿度，颗粒大小/形状等）。可以用来压制他们这将包括表面组装方面的一些新工作，这些工作已经在高蒸发速率下通过实验得到了证明[Li 2016]，但缺乏一个数学框架，无法给出与实验数据一致的结果。由于跟踪堵塞颗粒前沿的复杂性，许多现有的CRE模型仅限于轴对称几何形状。此外，这些模型不能捕捉到完整的蒸发过程中，由于在干燥的后期阶段出现的液滴表面的拓扑变化。使用有限元库Oomph-lib [Heil，Hazel 2006]，我们将开发一种新的CRE计算框架，以解决这两个问题。该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逐滴构建的打印线。分析和计算工作将与诺丁汉增材制造中心（CfAM）的合作伙伴一起进行，在那里定制的实验将使我们能够对我们的结果进行基准测试，并深入了解如何在我们的建模中捕获相关物理。

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.