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

你有没有想过，通过在固体基板上蒸发含有纳米颗粒的液体，可以获得各种各样的自组装沉积结构。沉积物的形状多种多样，从咖啡滴周围的环形到六角形的单元格和分形图案。一个由哥伦比亚大学科学家组成的跨学科团队将结合实验、理论和数值技术，研究相关的迷人的多尺度物理。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)。研究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图案(我们称为自上而下方法)，并通过识别图案中表示特定基本规律或运输规律的特征(自下而上方法)来研究。智能优点：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。第一个智能优点将是用相图描述纳米颗粒在固体基质上液体蒸发过程中的自组装。在这种情况下使用相图是新颖的，可以简单但有力地比较相互竞争的传输现象的大小，如润湿线上的蒸发、Marangoni再循环、静电和范德华力、浮力和介电。相图将提供多相过程之间复杂相互作用的洞察和概述，这些过程受液滴或膜的几何形状的影响：流体力学、热传递、传质、胶体相互作用。其次，现有的专有2D轴对称数值代码将扩展到3D(参见Chandra Collaboration Letter)，该代码具有能够非常精确地跟踪自由表面的移动网格。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液滴和液膜中自组装是一个具有挑战性的方法。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。我们将测试这样一个假设，即图案告诉我们关于创造它们的物理原理。广泛的影响：拟议的研究将提供创新的解决方案，在固体基质上形成纳米颗粒图案，并应用于有机电子和生物传感器的生物分子图案制作。将研究将打印分辨率提高两个数量级的方法(参见SonoPlot Letter)，并对均匀的颗粒层进行图案绘制。本提案中开发的模式识别算法将与法医专家麦克唐纳合作进行测试，以识别生物分子(见Zenhausern Letter)，并提高血迹模式分析的准确性(见合作Letter)。此外，在这项提案中开发的3D代码将作为开源代码免费分发，允许每一位感兴趣的科学家研究涉及液滴碰撞、液滴蒸发、胶片干燥等液滴和胶片传输现象的问题。这笔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.