Self-Assembly of Nanoparticles from Evaporating Drops and Liquid Films: Science, Engineering and Applications

你是否曾经对各种各样的自组装沉积结构感到惊讶，这些自组装沉积结构可以通过在固体基底上蒸发含有纳米颗粒的液体来获得。沉积物的形状各不相同，从咖啡滴周围的环，到六边形细胞和分形图案。一个由哥伦比亚大学科学家组成的跨学科团队将利用实验、理论和数值技术的结合，研究相关的迷人的多尺度物理学。该团队拥有以下技能：多相流（Attinger， PI），胶体（Somasundaran），模式识别（Chang）和开源计算流体动力学（Spiegelman）。纳米粒子的复杂自组装将通过使用第一物理原理来解释产生的自组装模式（我们称之为自上而下的方法），并通过识别模式中的特征来研究，这些特征是特定基本定律或传输规则的标志（自下而上的方法）。智力优势：实验将涉及到在各种基质上发现复杂流体的微滴，荧光显微镜和激光轮廓术来扫描三维沉积物。第一个智力优势将是用相图描述纳米颗粒在固体基板上液体蒸发过程中的自组装。在这种情况下，相图的使用是新颖的，它可以简单而有力地比较相互竞争的输运现象的大小，如湿润线的蒸发、马兰戈尼再循环、静电和范德华力、浮力和介电电泳。相图将提供一个洞察和多相过程之间复杂相互作用的概述，受液滴或膜的几何形状的影响：流体力学，传热，传质，胶体相互作用。其次，可用的专有2d轴对称数字代码，具有能够非常准确地跟踪自由表面的移动网格，将扩展到3D（见钱德拉合作信）。这将允许模拟更大范围的边界条件，允许考虑薄膜和复杂的几何形状。考虑到多重传输现象和时间/长度尺度，从第一性原理解释纳米粒子从蒸发滴和液体膜中的自组装是一种具有挑战性的方法。因此，我们还将开发一种基于自组装特征模式识别的自底向上方法。我们将验证这个假设，即这些图案告诉我们创造它们的物理原理。更广泛的影响：拟议的研究将提供创新的解决方案，在固体基质上图案纳米颗粒，应用于有机电子学和生物传感器的生物分子图案。将研究将打印分辨率提高两个数量级的方法（参见Sonoplot字母），并对均匀颗粒层进行图案绘制。与法医专家MacDonell合作，将测试本提案中开发的模式识别算法，以识别生物分子（见Zenhausern信）并提高血迹模式分析的准确性（见合作信）。此外，在本提案中开发的3D代码将作为开源代码免费分发，允许每个感兴趣的科学家研究涉及液滴和薄膜传输现象的问题，如液滴撞击、液滴蒸发、薄膜干燥。资金将支持一名研究生。

Have you ever wondered at the variety of self assembled deposit structures that can be obtained by evaporating liquids containing nanoparticles on top of a solid substrate. Deposit shapes vary from rings around a coffee drop, to hexagonal cells and fractal patterns. An interdisciplinary team of Columbia University scientists will study the related fascinating multiscale physics, using a combination of experimental, theoretical and numerical techniques. The team has the following skills: multiphase flow (Attinger, PI), colloids (Somasundaran), pattern recognition (Chang) and open-source computational fluid dynamics (Spiegelman). The complex self-assembly of nanoparticles will be studied by using first physical principles to explain the resulting selfassembled patterns (what we call a top-down approach), and by identifying features in the patterns that are signs of specific basic laws or transport rules (bottom-up approach).Intellectual Merit:Experiments will involve the spotting of microdrops of complex fluids on various substrates, fluorescence microscopy and laser profilometry to scan the three dimensional deposits. The first intellectual merit will be to describe with a phase diagram the self-assembly of nanoparticles during liquid evaporation on a solid substrate. The use of a phase diagram in that context is novel and allows a simple but powerful comparison of the magnitude of competing transport phenomena, such as evaporation at the wetting line, Marangoni recirculation, electrostatic and van der Waals forces, buoyancy, and dielectrophoresis. The phase diagram will provide an insight and an overview of the complex interplay between multiphase processes, influenced by the geometry of the liquid drop or film: fluid mechanics, heat transfer, mass transfer, colloidal interactions. Second, an available proprietary 2D-axisymmetric numerical code with a moving mesh able to very accurately track the free surface will be extended to 3D (see Chandra collaboration letter). This will allow the simulation of a wider ranges of boundary conditions, permitting the consideration of thin films and complex geometries. Explaining the self-assembly of nanoparticles from evaporating drops and liquid films from first principles is a challenging approach, given the multiple transport phenomena and time/length scales. Therefore, we will also develop a bottom-up approach based on pattern recognition of selfassembled features. We will test the hypothesis that the patterns tell us the about the physics that created them.Broader Impact:The proposed research will deliver innovative solutions to pattern nanoparticles on solid substrates, with applications in organic electronics and patterning of biomolecules for biosensors. Methods to increase printing resolution by two orders of magnitude (see Sonoplot letter), and to pattern uniform layers of particles will be investigated. The pattern recognition algorithms developed in this proposal will be tested to identify biomolecules (see Zenhausern letter) and enhance the accuracy of bloodstain pattern analysis, in collaboration with forensics expert MacDonell (see collaboration letter). Also, the 3D code developed in this proposal will be distributed freely as an open-source code, allowing every interested scientist to study problems involving drop and film transport phenomena such as drop impact, drop evaporation, film drying. Funding will support one graduate student.