Bazazi Parisa, Hejazi Seyed Hossein
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary AB T2N 1N4, Canada.
ACS Appl Mater Interfaces. 2022 May 4;14(17):20280-20290. doi: 10.1021/acsami.2c03156. Epub 2022 Apr 21.
Controlled transport of liquid droplets on solid surfaces is critical in many practical applications, such as self-cleaning surfaces, coating, drug delivery, and agriculture. Non-adhesive liquid drops levitate on solid surfaces; therefore, they are highly mobile and directed toward desired locations by external stimuli. Although research on liquid-repellent surfaces has proliferated, the existing methods are still limited to creating surface roughness or coating the liquid droplets. Here, we create non-contact aqueous drops on hydrophilic surfaces in an oleic environment and use them to deposit submicrometer droplets encapsulating nanoparticles on solid surfaces. A glass surface is buried under an oil phase that contains a high concentration of Span 80 surfactants, and a drop of silica nanoparticle dispersion is released on the solid surface. We study the effect of surfactant concentration in oil and nanoparticle concentration in water on wetting dynamics and report a plethora of droplet spreading regimes from fully wetting to non-wetting. We find a threshold Span 80 concentration above which surfactant assemblies are formed on the solid and prevent the direct contact of the drop with the surface. At the same time, water-in-oil emulsions are generated at the drop-oil interface. The drop moves and leaves a trace of emulsions with encapsulated nanoparticles on the solid. We demonstrate the possibility of local surface coating with hydrophilic nanoparticles in a hydrophobic medium. The developed methodology in this study is a generic approach facilitating the droplet patterning in numerous applications, from pharmaceutical polymetric carriers to the formulation of cosmetics, insecticides, and biomedical diagnoses.
液滴在固体表面的可控传输在许多实际应用中至关重要，例如自清洁表面、涂层、药物递送和农业领域。非粘性液滴悬浮在固体表面；因此，它们具有高度的流动性，并可通过外部刺激导向所需位置。尽管对拒液表面的研究大量涌现，但现有方法仍局限于制造表面粗糙度或包覆液滴。在此，我们在油酸环境中的亲水性表面上制造非接触水相液滴，并利用它们在固体表面沉积包裹纳米颗粒的亚微米级液滴。将玻璃表面埋于含有高浓度Span 80表面活性剂的油相之下，并在固体表面释放一滴二氧化硅纳米颗粒分散液。我们研究了油相中表面活性剂浓度和水中纳米颗粒浓度对润湿动力学的影响，并报告了从完全润湿到非润湿的大量液滴铺展状态。我们发现了一个Span 80浓度阈值，高于该阈值时，表面活性剂聚集体在固体上形成并阻止液滴与表面直接接触。与此同时，在液滴 - 油界面处产生油包水乳液。液滴移动并在固体上留下带有包裹纳米颗粒的乳液痕迹。我们展示了在疏水介质中用亲水性纳米颗粒进行局部表面涂层的可能性。本研究中开发的方法是一种通用方法，有助于在众多应用中进行液滴图案化，从药物聚合物载体到化妆品、杀虫剂的配方以及生物医学诊断。
