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鲜艳颜色源于光波对形成翅膀/羽毛的材料的结构顺序的干扰。与染料和颜料不同的是，结构色不吸收光线，而是从微观结构的表面反射光线。反射光的波长取决于对象的方向和视角，导致虹彩的闪烁、变色效果。这种结构颜色也可以通过将球形颗粒(200-500 nm)组装成紧密堆积在表面的晶体来产生。胶体晶体中颗粒的局部有序性由颗粒间的相互作用及其颗粒堆积效率决定。虽然目前可用的大多数实验研究的目标是最大化胶体晶体的尺寸，但在理解控制局部有序的因素及其对结构颜色的影响方面存在着显著的知识差距。由于组装过程中使用的实验参数和获得的相应结构之间存在复杂的相互作用，因此存在这种缺乏了解。了解胶体颗粒的结晶有序性与实验工艺参数之间的关系是当前提议的重点。这项建议将研究球形纳米粒子形成的局部组装对棒状粒子添加的影响，以及它们对应的对结构颜色亮度的影响。该项目将概述一种合成永不褪色的表面涂层的一般策略，而染料或颜料基漆则不是这样。目前使用的大多数材料是组装的纳米颗粒的基态和平衡相，它们具有明确的性质，但受到热力学的限制。为了突破材料设计的极限并在介观材料中编码出不寻常的性质，我们需要超越传统的平衡材料，进入非平衡的非球形粒子组装领域。目前，人们对非球形胶体组装体的形成原理知之甚少，对其结构-性质-功能关系更是知之甚少。这种知识差距的存在是由于非球形粒子组装过程中涉及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。这项提议旨在以棒状物和球状物作为纳米粒子的模型来理解这些方面。该提案将解决以下基本问题：(A)非球形粒子如何相互作用？影响粒子间相互作用的因素有哪些？(B)非球形颗粒的存在对球形纳米颗粒的结晶有何影响？(C)局部晶序的变化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实验，并利用液态透射电子显微镜(太平洋西北国家实验室)和X射线/光散射(路易斯安那州立大学)跟踪其组装动力学/动力学来解决。此外，还将开发理论模型，以更好地了解驱动组装的表面力，并帮助开发工艺路线，以合成具有可调特性(如结构颜色)的纳米级涂层。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。

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.