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佐治亚理工学院的莫汉·斯里尼瓦萨劳教授通过一种简单而优雅的方式创建有序的多孔聚合物结构，而不需要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，大气中的水凝结在聚合物溶液的冷表面上。水滴的自组装和随后的结晶在聚合物薄膜中产生了二维和三维(2D和3D)填充孔的有序阵列。凝结在冰冷的固体表面上的水滴在日常生活中的各种情况下都可以看到。这种现象的常见例子包括清晨树叶上结露，进入寒冷的房间时眼镜雾化，星巴克咖啡杯盖上凝结的水，以及在擦拭杯子时对着杯子呼吸。这项研究考察了“呼吸图形”现象--聚合物表面的冷凝--并为在非常短的时间内从各种聚合物构建宏观三维多孔结构铺平了一条新的途径。从这项研究中获得的基础知识可能会影响到超小体积的反应器、衍射光栅和细胞生长支架。此外，该项目还为本科生和研究生提供培训，强调其与本研究的结合。该项目还开发了与劳伦斯科学馆相关的推广项目，向公众传达这项研究的价值。在材料部凝聚态物理项目的支持下，斯里尼瓦萨劳教授的研究团队阐明了水分在寒冷表面凝结的机制，称为呼吸数字。虽然众所周知，大孔聚合物可以作为模板来制作具有二维孔洞的陶瓷和金属结构，但这些结构的形成机理还远未被了解。这项研究研究了呼吸图形自组装所涉及的现象的物理和物理化学。该团队研究了关键过程，如成核和生长、有序化动力学、不合并、表面张力驱动的不稳定性、球体堆积、热/质传输和润湿。这些测量是使用高速视频显微镜进行的。了解呼吸图形的形成动力学/机制以及由此产生的三维结构的光学/物理属性可能会导致一种简单而有效的方式，从各种聚合物快速创建有序的大孔结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.