Department of Chemical and Biological Engineering, Colorado School of Mines 1500 Illinois Street, Golden, Colorado 80401, United States.
Langmuir. 2017 Jun 13;33(23):5769-5776. doi: 10.1021/acs.langmuir.7b00547. Epub 2017 Jun 1.
Nonclose-packed colloidal arrays have many potential applications ranging from plasmonic sensors, light trapping for photovoltaics, to transparent electrodes. However, scalable fabrication of those structures remains a challenge. In this Article, we investigate the robustness of an electric-field assisted approach systematically. A monolayer of nonclose-packed crystalline array is first created under a low-frequency alternating-current electric field in solution. We then apply a sequence of direct-current pulses to fix the particle array onto the substrate so that it remains intact even after both field removal and solvent evaporation. Key process parameters such as the alternating-current field strength, direct-current magnitude, particle concentration, and solvent-evaporation rate that affect both ordering and fixing of colloidal particles have been studied systematically. We find that direct currents with an intermediate magnitude induce electrophoretic motion of particles toward the substrate and facilitate their permanent adhesion on the substrate due to strong van der Waals attraction. A higher current, however, causes lateral aggregation of particles arising from electroosmotic flow of solvent and destroys the periodic ordering between particles. This approach, in principle, can be conveniently adapted into the continuous convective assembly process, thus making the fabrication of nonclose-packed colloidal arrays scalable.
无密堆积胶体阵列在等离子体传感器、光伏光捕获到透明电极等方面具有许多潜在应用。然而，这些结构的可扩展制造仍然是一个挑战。在本文中，我们系统地研究了电场辅助方法的稳健性。首先在溶液中的低频交流电场下形成单层无密堆积晶体阵列。然后，我们施加一系列直流脉冲将颗粒阵列固定在基底上，即使在去除电场和溶剂蒸发后，颗粒阵列仍然保持完整。我们系统地研究了影响胶体颗粒有序化和固定的关键工艺参数，如交流场强、直流幅度、颗粒浓度和溶剂蒸发率。我们发现，中等幅度的直流电会引起颗粒向基底的电泳运动，并由于强范德华吸引力而促进它们在基底上的永久附着。然而，更高的电流会由于溶剂的电渗流而导致颗粒的横向聚集，并破坏颗粒之间的周期性有序。该方法原则上可以方便地适应连续对流组装过程，从而使无密堆积胶体阵列的制造具有可扩展性。
