Langmuir. 2018 Apr 17;34(15):4515-4525. doi: 10.1021/acs.langmuir.8b00230. Epub 2018 Apr 3.
The unique drying behavior of aqueous droplets that contain soft hydrogel microspheres (microgels) upon evaporation was systematically investigated. Compared to the ring-shaped deposits that are obtained from drying solid microsphere dispersions, we have previously reported that uniformly ordered thin films are obtained from drying ∼1.2 μm-sized poly( N-isopropyl acrylamide) microgel dispersions. In the present study, we thoroughly investigated several hitherto unexplored aspects of this self-organization, such as the effect of the size, chemical structure, and "softness" of the microgels (or rigid microspheres). For the macro- and microscopic observation of the drying behavior of various microsphere dispersions, an optical microscope and a digital camera were employed. The results suggested that the convection in the aqueous droplets plays an important role for the transportation of the microgels to the air/water interface, where the softness and surface activity of the microgels strongly affects the adsorption of the microgels. On the basis of these discoveries, a design concept for the rapid formation of uniform thin films of soft microgels was proposed.
系统研究了含有软水凝胶微球（微凝胶）的水相液滴在蒸发时的独特干燥行为。与从干燥固体微球分散体中获得的环形沉积物相比，我们之前曾报道过，从干燥尺寸约为 1.2μm 的聚（N-异丙基丙烯酰胺）微凝胶分散体中可以获得均匀有序的薄膜。在本研究中，我们深入研究了这种自组织的几个迄今为止尚未探索的方面，例如微凝胶（或刚性微球）的尺寸、化学结构和“柔软度”的影响。为了宏观和微观观察各种微球分散体的干燥行为，使用了光学显微镜和数码相机。结果表明，水相液滴中的对流对于微凝胶向气/水界面的输运起着重要作用，其中微凝胶的柔软性和表面活性强烈影响微凝胶的吸附。在此基础上，提出了一种快速形成软微凝胶均匀薄膜的设计概念。
