Department of Mechanical Engineering , State University of New York at Binghamton , 4400 Vestal Parkway East , Binghamton , New York 13902 , United States.
Langmuir. 2018 Jun 26;34(25):7445-7454. doi: 10.1021/acs.langmuir.8b01308. Epub 2018 Jun 13.
We report on the use of electrospray atomization to deliver nanoparticles and surfactant directly to the surface of sessile droplets. The particles delivered to the target droplet remained adsorbed at its interface since they arrived solvent-free. Upon complete evaporation, the interface of the target drop was mapped to the underlying substrate, forming a nanoparticle deposit. The use of electrospray permitted the exploration of the interfacial particle transport and the role of surfactants in governing particle motion and deposit structure. When no surfactant was present in the sprayed solution, there was no observable convection of the interfacial particles. When Tween 80, a high-molecular-weight surfactant, was added to the sprayed solution, the surface flow was similarly suppressed. Only when small surfactants (e.g., sodium dodecyl sulfate) were present in the sprayed solution was Marangoni flow, directed toward the droplet apex, induced at the interface. This flow drove the interfacial particles to the apex of the target droplet, creating a particle-dense region at the center of the final deposit. We found that small surfactants were capable of desorbing from the interface at a sufficiently high rate relative to the evaporation time scale of the target droplet. Once inside the drop, the desorbed surfactant was convected to the contact line where it accumulated, inducing a surface tension gradient and a solutal Marangoni flow. Numerical modeling using the lattice Boltzmann-Brownian dynamics method confirmed this mechanism of particle transport and its relationship to deposit structure. The use of sacrificial targets combined with electrospray may provide a unique capability for building colloidal monolayers with organized structure in a scalable way.
我们报告了使用电喷雾雾化将纳米颗粒和表面活性剂直接输送到液滴的表面。由于它们是无溶剂到达目标液滴的，因此输送到目标液滴的颗粒仍然吸附在其界面上。在完全蒸发后，目标液滴的界面被映射到底层基底上，形成纳米颗粒沉积物。使用电喷雾可以探索界面颗粒输运以及表面活性剂在控制颗粒运动和沉积物结构中的作用。当喷涂溶液中没有表面活性剂时，界面颗粒没有观察到对流。当喷涂溶液中添加了高分子量表面活性剂吐温 80 时，表面流也被类似地抑制。只有当喷涂溶液中存在小分子表面活性剂（例如十二烷基硫酸钠）时，才会在界面上诱导指向液滴顶点的马兰戈尼流。这种流动将界面颗粒驱动到目标液滴的顶点，在最终沉积物的中心形成一个颗粒密集区域。我们发现，小分子表面活性剂能够以足够高的速率从界面解吸，相对于目标液滴的蒸发时间尺度。一旦进入液滴内部，解吸的表面活性剂被对流到接触线，在那里它会聚集，诱导表面张力梯度和溶质马兰戈尼流。使用格子玻尔兹曼-布朗动力学方法的数值模拟证实了这种颗粒输运机制及其与沉积物结构的关系。使用牺牲目标物与电喷雾相结合的方法可能为以可扩展的方式构建具有组织化结构的胶体单层提供独特的能力。
