Self-Assembly of Levitating Water Droplets over Polymer Solutions for Fabrication of Microporous Structures

材料研究部的凝聚态物理项目支持乔治亚理工学院的Mohan Srinivasarao教授通过一种简单而优雅的方式创造出有序的多孔聚合物结构，而无需使用缓慢或昂贵的制造工艺。当挥发性溶剂中的聚合物蒸发时，会导致溶液冷却。然后，大气中的水在聚合物溶液的冷表面凝结。水滴的自组装和随后的结晶在聚合物薄膜中产生有序的二维和三维（2D和3D）填充孔阵列。水滴在冰冷的固体表面凝结的现象在日常生活中随处可见。这种现象的常见例子包括：清晨树叶上结露水，进入寒冷的房间时眼镜上起雾，星巴克咖啡杯盖上凝结的水，以及擦玻璃时对着玻璃呼吸。本研究考察了“呼吸图”现象，即聚合物表面的缩合现象，为在很短的时间内用多种聚合物构建宏观三维多孔结构铺平了新的道路。从这项研究中获得的基础知识可能会影响到超小体积反应器、衍射光栅和细胞生长支架。此外，本项目提供本科生和研究生的培训，重点是与本研究的结合。该项目还开发了与劳伦斯科学馆（Lawrence Hall of Science）相关的外展项目，向公众宣传这项研究的价值。在材料部凝聚态物理项目的支持下，Srinivasarao教授的研究小组阐明了在冷表面上被称为呼吸图的水分凝结现象背后的机制。虽然已知大孔聚合物可以作为模板来制作具有二维孔的陶瓷和金属结构，但其结构形成的机制尚不清楚。本研究从物理和物理化学的角度研究呼吸图自组装过程中所涉及的现象。该团队研究了关键过程，如成核和生长、有序动力学、非聚结、表面张力驱动的不稳定性、球体的堆积、热/质量传递和润湿。这些测量是通过使用高速视频显微镜进行的。了解呼吸图的形成动力学/机制以及由此产生的三维结构的光学/物理性质可能会导致一种简单有效的方法，可以从各种聚合物中快速创建有序的大孔结构。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Condensed Matter Physics Program in the Division of Materials Research supports Professor Mohan Srinivasarao at Georgia Institute of Technology to create well-ordered porous polymeric structures via a simple and elegant way without using slow or costly fabrication processes. When a polymer in a volatile solvent is evaporated, it results in cooling of the solution. Water from the atmosphere then condenses on the cold surface of the polymer solution. The self-assembly and subsequent crystallization of water droplets produce an ordered array of two- and three-dimensionally (2D and 3D) packed holes in the polymer film. Water droplets condensing on a cold solid surface is seen in a variety of situations in everyday life. Common examples of this phenomenon include dew formation on leaves early in the morning, fogging of eyeglasses when one enters a cold room, water condensing on the lids of coffee cups from Starbucks, and breathing on glass as one polishes it. This research examines the phenomenon of "breath figures" - the condensation on a polymer surface - and paves a new way to construct macroscopic 3-dimensional porous structures from a variety of polymers in a very short time. The fundamental knowledge gained from this study may impact ultrasmall volume reactors, diffraction gratings, and to cell growth scaffolds. In addition, this project provides training of undergraduate and graduate students with emphasis on its integration with this research. The project also develops outreach programs connected to Lawrence Hall of Science to communicate the value of this research to the public.With this support from Condensed Matter Physics Program in the Division of Materials, Professor Srinivasarao’s research team elucidates the mechanism behind the phenomenon of moisture condensing on a cold surface called breath figures. Although it is known that macroporous polymers could be used as a template to make ceramic and metallic structures with 2-dimensional pores, the mechanism by which the structures form is far from understood. This research studies the physics and physical chemistry of the phenomena involved in the self-assembly of breath figures. The team investigates key processes such as nucleation and growth, ordering dynamics, noncoalescence, surface tension driven instabilities, packing of spheres, and heat/mass transport, and wetting. These measurements are carried out by using high-speed video microscopy. Understanding the formation kinetics/mechanism of breath figures and the optical/physical properties of the resulting 3-dimensional structures may lead to a simple and effective way to rapidly create ordered, macroporous structures from a variety of polymers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.