Beroz Justin, Bedewy Mostafa, Reinker Michael, Chhajer Vipul, Awtar Shorya, Hart A John
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA.
Rev Sci Instrum. 2012 Jan;83(1):015104. doi: 10.1063/1.3673680.
Capillary forces provide a ubiquitous means of organizing micro- and nanoscale structures on substrates. In order to investigate the mechanism of capillary self-assembly and to fabricate complex ordered structures, precise control of the meniscus shape is needed. We present a precision instrument that enables deposition of liquid droplets spanning from 2 nl to 300 μl, in concert with mechanical manipulation of the liquid-substrate interface with four degrees of freedom. The substrate has sub-100 nm positioning resolution in three axes of translation, and its temperature is controlled using thermoelectric modules. The capillary tip can rotate about the vertical axis while simultaneously dispensing liquid onto the substrate. Liquid is displaced using a custom bidirectional diaphragm pump, in which an elastic membrane is hydraulically actuated by a stainless steel syringe. The syringe is driven by a piezoelectric actuator, enabling nanoliter volume and rate control. A quantitative model of the liquid dispenser is verified experimentally, and suggests that compressibility in the hydraulic line deamplifies the syringe stroke, enabling sub-nanoliter resolution control of liquid displacement at the capillary tip. We use this system to contact-print water and oil droplets by mechanical manipulation of a liquid bridge between the capillary and the substrate. Finally, we study the effect of droplet volume and substrate temperature on the evaporative self-assembly of monodisperse polymer microspheres from sessile droplets, and demonstrate the formation of 3D chiral assemblies of micro-rods by rotation of the capillary tip during evaporative assembly.
毛细管力提供了一种在基底上组织微米和纳米尺度结构的普遍方法。为了研究毛细管自组装的机制并制造复杂的有序结构，需要精确控制弯月面形状。我们展示了一种精密仪器，它能够沉积体积从2纳升到300微升的液滴，并能对液 - 固界面进行四个自由度的机械操控。基底在三个平移轴上具有亚100纳米的定位分辨率，其温度通过热电模块控制。毛细管尖端可以绕垂直轴旋转，同时将液体滴到基底上。液体通过一个定制的双向隔膜泵进行输送，其中一个弹性膜由一个不锈钢注射器进行液压驱动。注射器由一个压电致动器驱动，实现纳升级别的体积和速率控制。对液体分配器的定量模型进行了实验验证，结果表明液压管路中的可压缩性会减小注射器的行程，从而实现毛细管尖端液体输送的亚纳升分辨率控制。我们使用这个系统通过对毛细管和基底之间的液桥进行机械操控来接触打印水和油滴。最后，我们研究了液滴体积和基底温度对来自静止液滴的单分散聚合物微球蒸发自组装的影响，并展示了在蒸发组装过程中通过毛细管尖端的旋转形成微棒的三维手性组装体。
