Understanding shape control in gold nanoparticles from molecular dynamics simulations

在这个建议中，我们的目标是在金纳米棒的生长使用原子模拟方法的初始步骤的微观理解。这里的创新点是对金纳米颗粒表面及其与分散在其中的电解质溶液（即溶剂分子、表面活性剂和离子）的相互作用的原子描述。材料科学的一个基本目标是设计和合成具有定制形状和尺寸的材料。在过去的十年中，各种尺寸和形状的金和银纳米颗粒的合成取得了巨大的进展。纳米金属颗粒具有多种功能特性，在电子学、光子学、生物纳米复合材料、（生物）化学传感和成像以及药物输送等领域具有广阔的应用前景，而控制金属纳米颗粒形状的基础是对晶体生长的微观理解。结晶是一个非平衡过程，扩散、活化势垒、表面能和特定晶体上的吸收动力学都会影响所得颗粒的形状，这对物理学家和化学家来说仍然是一个开放的挑战。颗粒形态和晶体结构是由有机表面活性剂和金属/卤化物离子浓度控制的，这是一个复杂的过程，目前还不清楚。棒状形状的生长意味着杆端的生长速度比侧面快。人们提出了不同的生长机制来解释金纳米棒在溶液中的生长。在不同的建议中，空间化学因素的相互作用，包括金属表面与表面活性剂的特定相互作用。我们在此要解决的问题包括：-表面活性剂胶束的形成，特别强调离子负载机制和在胶束上建立的z-电位;-表面活性剂双层在金属表面上的堆积，特别是堆积对于不同面的作用;-静电双层：我们要理解（i）抗衡离子分布;（ii）界面的电位降，特别是比较不同表面的电位差; -描述双层的扩散机制;特别是我们希望研究表面活性剂双层与胶束结合的金离子之间的相互作用。使用同步光学光谱和时间分辨小角X射线散射在同步加速器X射线源，他们可以直接监测的各向异性生长动力学的金和金铜纳米棒，并提取两个晶体方向（沿着杆的长轴和短轴）独立的生长参数。

In this proposal we aim to a microscopic understanding of the initial steps in the gold nanorods growth using an atomistic simulation approach. The innovative aspect here is the atomistic description of the surface of the gold nanoparticle and their interaction with the electrolyte solution where they are dispersed, namely with solvent molecules, surfactants and ions.A fundamental goal in material science is the design and synthesis of materials with tailored shape and size. The last decade has seen a tremendous progress in the synthesis of gold and silver nanoparticles of various sizes and shapes. Nanoscale metallic particles exhibit a variety of functional properties with promising applications in electronics, photonics, biologically inspired nanocomposites, (bio)chemical sensing and imaging and drug delivery.The fundamental step to control the shape of metal nanoparticles, is the microscopic understanding of the crystal growth. The crystallization is a non-equilibrium process and diffusion, activation barriers, surface energies and kinetics of the absorption on a specific crystal, all influence the shape of the the resulting particle providing a still open challenge for physicists and chemists. The particle morphology and crystal structure are controlled in a complex and currently poorly understood process by organic surfactants and metal/halide ions concentration.The growth of a rod-like shape implies that the rod ends grow at a faster rate than the sides. Different growth mechanisms have been proposed to explain the growth of gold nanorods in solution. Among the different proposals is the interplay of sterical chemical factors, including the specif interaction of the metal surfaces with the surfactants. The questions we would like to address here include: - surfacatants micelles formation, with particular emphasis to the the ion loading mechanism and the z-potential which builds up on the micelles;- packing of the surfactant bilayer on the metal surface, in particular role of packing for different facets;- the electrostatic double layer: we would like to understand (i) the counterions distribution; (ii) the potential drop across the interface, comparing in particular the difference in the potential for the different surfaces; - the description of the diffusion mechanism across the bilayer; in particular we want to investigate the interaction between the surfactant double layer and the micelles-bound gold ion.The project will be performed in close collaboration of the experimentalists. Using simultaneous optical spectroscopy and time-resolved small-angle X-ray scattering at a synchrotron X-ray source, they can directly monitor the anisotropic growth kinetics of gold and gold-copper nanorods and extract the growth parameters for both crystal directions (along the rod‘s long and short axes) independently.