Talbot Emma L, Yow Huai N, Yang Lisong, Berson Arganthaël, Biggs Simon R, Bain Colin D
Department of Chemistry and ‡School of Engineering and Computing Sciences, Durham University , South Road, Durham, DH1 3LE, U. K.
ACS Appl Mater Interfaces. 2015 Feb 18;7(6):3782-90. doi: 10.1021/am5087177. Epub 2015 Feb 4.
Printing of droplets of pure solvents containing suspended solids typically leads to a ring stain due to convective transport of the particles toward the contact line during evaporation of the solvent. In mixtures of volatile solvents, recirculating cells driven by surface tension gradients are established that lead to migration of colloidal particles toward the center of the droplet. In favorable cases, a dense disk of particles forms with a diameter much smaller than that of the droplet. In the latter stages of drying, convective transport of the particles radially toward the contact line still occurs. Two strategies are described to fix the distribution of particles in a compact disk much smaller than the initial diameter of the drying droplet. First, a nanoparticulate clay is added to induce an evaporation-driven sol-gel transition that inhibits convective flow during the latter stages of drying. Second, a nonadsorbing polymer is added to induce depletion flocculation that restricts particle motion after the particles have been concentrated near the center of the droplet. The area of the resulting deposit can be as little as 10% of the footprint of the printed droplet.
打印含有悬浮固体的纯溶剂液滴时，由于在溶剂蒸发过程中颗粒向接触线的对流传输，通常会导致环状污渍。在挥发性溶剂的混合物中，会形成由表面张力梯度驱动的循环单元，这会导致胶体颗粒向液滴中心迁移。在有利的情况下，会形成一个直径远小于液滴直径的致密颗粒盘。在干燥的后期阶段，颗粒仍会径向向接触线进行对流传输。本文描述了两种策略来将颗粒分布固定在一个比干燥液滴初始直径小得多的致密盘中。第一，添加纳米颗粒粘土以诱导蒸发驱动的溶胶-凝胶转变，从而在干燥后期抑制对流流动。第二，添加非吸附性聚合物以诱导耗尽絮凝，在颗粒集中在液滴中心附近后限制颗粒运动。所得沉积物的面积可低至打印液滴足迹的10%。
