The particle laden sessile drops when dried on solid surfaces under certain conditions leave a deposit pattern wherein all the particles are confined to a narrow region close to the edge of the deposit. Such patterns which often form when coffee drops dry are referred to as the coffee ring patterns or the coffee stains. Recent research points to the formation of intriguing patterns when colloidal particle laden drops are dried in configurations other than sessile mode. In this article, the combined effect of particle size and wettability of the substrate on the patterns formed by drying drops in sessile and pendant configurations is investigated via experiments. Our results demonstrate a transition from coffee ring to central dome-like deposit morphology with decrease in wettability of the substrates when drops containing 3 μm diameter particles are dried in pendent mode. A similar transition in the deposit morphology is observed with increase in the diameter of the particles in pendant drops dried on substrates of near neutral wettability (θ = 86 ± 3°). The influence of particles size, substrate wettability and drop configuration on the kinetics of deposition of particles at the three phase contact line will also be discussed. We compare our experimental observations with particle based simulations wherein the dried patterns are generated by accounting for three particle transport modes, namely, advective particle transport resulting from capillary flow, gravity driven settling of particles and particle capture by descending interface.

中文翻译：

---

干燥悬垂液滴中的粒径和基材润湿性相关模式

当在某些条件下在固体表面上干燥时，载有颗粒的固着液滴会留下沉积图案，其中所有颗粒都被限制在靠近沉积边缘的狭窄区域内。这种在咖啡滴干燥时经常形成的图案被称为咖啡环图案或咖啡渍。最近的研究指出，当载有胶体颗粒的液滴以固定模式以外的配置干燥时，会形成有趣的模式。在本文中，通过实验研究了颗粒尺寸和基材的润湿性对干燥液滴形成的无柄和悬垂结构图案的综合影响。我们的结果表明，当含有 3 μm 直径颗粒的液滴以悬垂模式干燥时，基板的润湿性会从咖啡环转变为中央圆顶状沉积物形态。随着在接近中性润湿性 (θ = 86 ± 3°) 的基材上干燥的悬垂液滴中颗粒直径的增加，观察到沉积形态的类似转变。还将讨论颗粒尺寸、基材润湿性和液滴配置对颗粒在三相接触线处沉积动力学的影响。我们将我们的实验观察结果与基于粒子的模拟进行比较，其中干燥模式是通过考虑三种粒子传输模式产生的，即由毛细流动产生的平流粒子传输，