Department of Health Sciences and Technology, ETH Zurich, 8092 Zurich, Switzerland.
Department of Materials, ETH Zurich, 8092 Zurich, Switzerland.
ACS Nano. 2023 Feb 14;17(3):3098-3106. doi: 10.1021/acsnano.2c12065. Epub 2023 Jan 31.
Drying a colloidal droplet involves complex physics that is often accompanied by evaporation-induced concentration gradients inside of the droplet, offering a platform for fundamental and technological opportunities, including self-assembly, thin film deposition, microfabrication, and DNA stretching. Here, we investigate the drying, liquid crystalline structures, and deposit patterns of colloidal liquid crystalline droplets undergoing liquid-liquid crystalline phase separation (LLCPS) during evaporation. We show that evaporation-induced progressive up-concentration inside the drying droplets makes it possible to cross, at different speeds, various thermodynamic stability states in solutions of amyloid fibril rigid filamentous colloids, thus allowing access to both metastable states, where phase separation occurs via nucleation and growth, as well as to unstable states, where phase separation occurs via the more elusive spinodal decomposition, leading to the formation of liquid crystalline microdroplets (or tactoids) of different shapes. We present the tactoids "phase diagram" as a function of the position within the droplet and elucidate their hydrodynamics. Furthermore, we demonstrate that the presence of the amyloid fibrils not only does not enhance the pinning behavior during droplet evaporation but also slightly suppresses it, thus minimizing the coffee-ring effect. We observed that microsize domains with cholesteric structure emerge in the drying droplet close to the droplet's initial edge, yet such domains are not connected to form a uniform cholesteric dried film. Finally, we demonstrate that a fully cholesteric dried layer can be generated from the drying droplets by regulating the kinetics of the evaporation process.
干燥胶体液滴涉及复杂的物理过程，通常伴随着液滴内的蒸发诱导浓度梯度，为基础和技术机会提供了平台，包括自组装、薄膜沉积、微制造和 DNA 拉伸。在这里，我们研究了胶体液晶液滴在蒸发过程中发生液-液相分离（LLCPS）时的干燥、液晶结构和沉积模式。我们表明，干燥液滴内的蒸发诱导逐渐浓缩使得有可能以不同的速度跨越在淀粉样原纤维刚性丝状胶体溶液中的各种热力学稳定状态，从而既可以进入相分离通过成核和生长发生的亚稳状态，也可以进入通过更难以捉摸的旋节分解发生相分离的不稳定状态，导致形成不同形状的液晶微液滴（或微胶束）。我们提出了作为液滴内位置函数的微胶束“相图”，并阐明了它们的流体动力学。此外，我们证明了淀粉样原纤维的存在不仅不会增强液滴蒸发过程中的钉扎行为，反而会轻微抑制它，从而最小化咖啡环效应。我们观察到在靠近液滴初始边缘的干燥液滴中出现具有胆甾相结构的微尺寸域，但这些域没有连接形成均匀的胆甾相干燥膜。最后，我们通过调节蒸发过程的动力学证明了可以从干燥液滴中生成完全的胆甾相干燥层。
