RII Track-4:NSF: Understanding the role of surface interactions in co-assembly of spherical and rod-shaped colloids

在自然界中，蝴蝶翅膀、孔雀羽毛和甲虫甲壳的绚丽色彩源于光波与构成翅膀/羽毛的材料的结构秩序的干涉。与染料和颜料相比，结构色不吸收光线，而是反射来自微观结构表面的光线。反射光的波长取决于物体的方向和观察角度，产生闪烁的、变色的彩虹效果。这种结构颜色也可以通过将球形颗粒（200-500纳米）组装成表面上紧密排列的晶体来产生。胶体晶体中粒子的局部有序是由粒子间的相互作用和粒子堆积效率决定的。虽然目前大多数可用的实验研究旨在最大化胶体晶体的大小，但在理解局部秩序的控制因素及其对结构颜色的影响方面存在显着的知识差距。由于装配过程中使用的实验参数与获得的相应结构之间存在复杂的相互作用，因此缺乏理解。了解胶体颗粒的结晶顺序与实验工艺参数之间的关系是当前建议的重点。本提案将研究球形纳米颗粒形成的局部组装对棒状颗粒添加的影响，以及它们对结构颜色亮度的相应影响。该项目将概述一种合成永不褪色的表面涂层的总体策略，这与染料或颜料为基础的油漆不同。目前使用的大多数材料都是基态，即组装的纳米颗粒的平衡相，它们具有明确的性质，但受热力学的限制。为了突破材料设计的极限，在介观材料中编码不寻常的特性，我们需要超越传统的平衡材料，进入非球形粒子的非平衡组合领域。目前，人们对非球形胶体的形成原理缺乏了解，对其结构-性能-功能关系的了解更少。这种知识差距的存在是由于涉及非球形粒子组装的粒子间相互作用的固有复杂性，相应的动力学和控制参数。本研究旨在利用棒状和球形纳米粒子作为模型来了解这些方面。该提案将解决以下基本问题：(a)非球形粒子如何相互作用？哪些因素影响粒子间的相互作用？(b)非球形颗粒的存在对球形纳米颗粒结晶的影响是什么？(c)局部晶体顺序的改变如何影响组装材料的光学性质？这些问题将通过对金纳米棒和纳米球进行系统的实验来解决，并使用液相透射电子显微镜（在太平洋西北国家实验室）和x射线/光散射（在路易斯安那州立大学）跟踪其组装动力学/动力学。此外，将开发理论模型，以更好地理解驱动组装的表面力，并协助开发加工路线，以合成具有可调性能（如结构色）的纳米级涂层。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。

In nature, the brilliant colors of butterfly wings, peacock feathers, and beetle carapaces originate from the interference of light waves with the structural order in the material forming the wings/feathers. In contrast to dyes and pigments, structural colors do not absorb light but instead reflect it from a microscopically structured surface. The wavelengths of reflected light depending on the orientation of the object and the viewing angle, causing the shimmery, color-shifting effect of iridescence. This structural color can be also produced by assembling spherical particles (200-500 nm) into close-packed crystals on surfaces. The local ordering of the particles within a colloidal crystal is governed by the interaction between particles, and their particle packing efficiency. While most of the currently available experimental studies aim at maximizing the size of colloidal crystals, there is a significant knowledge gap in understanding the factors governing local order and its impact on structural color. This lack of understanding exists due to a complex interplay between the experimental parameters used in the assembly process and the corresponding structure obtained. Understanding the relationship between the crystal order of colloidal particles and the experimental processing parameters is the focus of the current proposal. This proposal will investigate the impact of the local assembly formed by spherical nanoparticles upon the addition of rod-shaped particles, and their corresponding on the brilliance of structural color. The project will outline a general strategy for synthesizing surface coatings with never fading colors, which is not the case for dye or pigment-based paints.The majority of currently used materials are the ground state, equilibrium phases of the assembled nanoparticles, which have well-defined properties but are bound by the limits of thermodynamics. To push the limits of material design and encode unusual properties in the mesoscopic materials, we need to look beyond the conventional equilibrium materials into the domain of non-equilibrium assemblies of non-spherical particles. Currently, there is a significant lack of understanding of principles governing the formation of assemblies of non-spherical colloids, and even less is known about their structure-property-function relationships. This knowledge gap exists due to the inherent complexity of the interparticle interactions involved in the assembly of non-spherical particles, corresponding dynamics, and control parameters. This proposal aims at understanding these aspects using rods and spheres as model nanoparticles. The proposal will address the following fundamental questions: (a) How do non-spherical particles interact? and which factors influence the interparticle interactions? (b) What is the effect of the presence of non-spherical particles on the crystallization of spherical nanoparticles? (c) How does the change in local crystalline order affect the optical properties of the assembled material? These questions will be addressed by performing systematic experiments on gold nanorods and nanospheres and following their assembly dynamics/kinetics using liquid-phase transmission electron microscopy (at Pacific Northwestern National Laboratory) and x-ray/light scattering (at Louisiana State University). Additionally, theoretical models will be developed which will provide a better understanding of the surface forces driving the assembly and assist in developing processing routes to synthesize nanoscale coatings of tunable properties such as structural color.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.