Koyama Naoto, Hanasaki Itsuo
Institute of Engineering, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo 184-8588, Japan.
Soft Matter. 2021 May 12;17(18):4826-4833. doi: 10.1039/d1sm00315a.
Sessile droplets of colloidal dispersions tend to exhibit the coffee-ring phenomenon in the drying process. The suspended particles are transported especially at the final stage of the drying process, which is called the rush hour. Conventional inkjet printers require the ink liquid to have a sufficiently low viscosity for inkjet discharge, but such liquids tend to be subject to the coffee-ring effect. The coffee-ring effect is an issue for conventional printing applications and drawing wires in printed electronics. We show by microscopy movie data analysis based on single particle tracking that the addition of a small amount of cellulose nanofibers (CNFs) to the colloidal dispersion works in such a way that the initial low concentration satisfies the low viscosity requirement, and the three-dimensional structural order of the CNFs formed during the final stage of droplet drying owing to the high concentration hinders the transport of particles to the periphery, suppressing the coffee-ring effect. This is a spatio-temporally controlled process that makes use of the inherent process of ordinary ink printing situations by the simple protocol. This is also an approach to seamlessly link the ink and substrate since CNFs are regarded as a promising substrate material for flexible devices in printed electronics because of their fine texture that keeps conductive nanoparticles on the surface.
胶体分散体的 sessile 液滴在干燥过程中往往会出现咖啡环现象。悬浮颗粒尤其在干燥过程的最后阶段被输送，这一阶段被称为高峰期。传统喷墨打印机要求墨液具有足够低的粘度以便进行喷墨排放，但这类液体往往容易受到咖啡环效应的影响。咖啡环效应是传统印刷应用和印刷电子中绘制导线时面临的一个问题。我们通过基于单粒子跟踪的显微镜电影数据分析表明，向胶体分散体中添加少量纤维素纳米纤维（CNF）的作用方式是，初始的低浓度满足低粘度要求，而在液滴干燥最后阶段由于高浓度形成的 CNF 的三维结构秩序阻碍了颗粒向周边的输送，从而抑制了咖啡环效应。这是一个时空可控的过程，通过简单的方案利用了普通油墨印刷情况的固有过程。这也是一种无缝连接油墨和基材的方法，因为由于 CNF 具有能使导电纳米颗粒保持在表面的精细质地，所以它被视为印刷电子中柔性器件的一种有前途的基材材料。
