Analysis of impact dynamics and deposition of single and multiple PEDOT:PSS solution droplets
In line with recent efforts and developments in emerging printed electronics, using solution-processed coatings, we studied the impact dynamics and deposition of single and multiple polymeric aqueous and isopropanol (IPA)-diluted PEDOT:PSS solution droplets, across seven orders of magnitude timescale. The solution properties and release height of droplets from a needle were varied to generate Weber numbers in the range of 94–510, with two Ohnesorge numbers of 0.0108 and 0.0195, for aqueous and IPA-diluted PEDOT:PSS solution droplets, respectively. The former droplet on FTO glass substrate is partially wetting, whereas the latter is fully wetting, generating different phenomena in the prolonged wetting and drying time. The solutions showed shear-thinning behavior at high shear rates, but viscosity immediately reached a saturated limit at higher shear rates and, therefore, the fluids behaved as Newtonian fluids during impact. Among the results, the addition of IPA resulted in improved spreading of PEDOT:PSS in the wetting phase, with wetting trend following the Tanner’s law. We then assessed the prediction power of existing models to predict maximum spreading, taking into account the role of measured static and dynamic contact angles during spreading. Multiple droplets (2, 5, and 15) were impacted nearly simultaneously and formed lines and films. We examined the bridge formation, spreading length growth, and shape evolution of multiple coalescing droplets. We also correlated the formed surface area with the number of coalescing droplets and discussed the ideality of the shape of the formed film. The results of this study will help to pave the way for large-scale manufacturing of organic coatings using droplet-based methods.
We acknowledge the financial support from the Shanghai Municipal Education Commission via the Oriental Scholar fund and the funding form the National Natural Science Foundation of China (NSFC). We thank Prof. Yunlong Guo and Miao Huo of the University of Michigan-Shanghai Jiaotong University Joint Institute for assisting with the rheology equipment and measurements. D. B. acknowledges the scholarship from the Chinese government.
DB and ME devised the project. DB performed the experiments and analyses, prepared the figures and drafted the manuscript. ME revised the manuscript and improved the interpretation of the results. ME conceived and outlined the project direction and objectives and secured research funding.
Compliance with ethical standards
Conflict of interest
The authors declare no competing interests.
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