CAREER: Understanding the Interactions Between Surfactants and Metallic Nanoparticles Using Molecular Simulation

纳米粒子大约比人类头发的宽度小1000倍。人们已经发现金属纳米粒子在许多方面都很有用，比如摧毁我们体内的癌细胞，增强人体器官的成像，催化化学反应以减少不想要的副产品，提高油漆和涂料的性能，以及制造纳米级电子设备和光伏电池组件。在每种情况下，都需要特定形状的纳米颗粒。表面活性剂（类似肥皂的物质）倾向于牢固地附着在金属表面上。当表面活性剂附着在生长的纳米晶体的特定表面区域以控制其切面的相对生长速率时，这使得合成所需形状的金属纳米颗粒成为可能。附着的表面活性剂也会影响这些纳米颗粒如何聚集在一起形成有序的排列，这是纳米制造过程的关键促成因素。目前，我们对表面活性剂/金属纳米颗粒相互作用的理解存在重大差距，这阻碍了预期应用的进展。部分困难在于纳米颗粒的尺寸极小，这使得对许多工作过程的观察超出了实验研究的范围。另一个挑战是影响表面活性剂在金属纳米颗粒上的附着和堆积的因素很多。在这项工作中，我们将使用计算机模型对不同化学组成的表面活性剂如何附着在金属纳米颗粒的不同表面进行系统研究。在这个项目中，计算机模型将在分子的长度尺度上探测系统的行为，从而提供对这些动态过程的详细了解，使优化纳米颗粒生长条件成为可能。这项研究将伴随着一个重要的教育组成部分。为引导初高中学生进入stem领域，将制作以教育策略为基础的电脑游戏。研究的内容将纳入教学课程，并将开展教育推广活动，以吸引俄亥俄州阿巴拉契亚地区的成员。本CAREER项目的总体研究目标是通过分子模拟，对水介质中金属纳米颗粒（MNPs）与表面活性剂分子之间的相互作用有一个基本的了解。MNPs由于其独特的电学、热学和光学特性而越来越引起人们的兴趣，并在生物成像、药物输送、分子传感器、纳米制造、光热治疗和多相催化等领域得到了应用。这些不同的技术应用通常涉及MNPs与表面活性剂的相互作用。由于表面活性剂对金属-水界面具有很强的亲和力，表面活性剂在这些界面上以高密度有序的形态吸附。这些表面结构通过表面活性剂的烷基尾部之间的疏水相互作用以及强极性头-金属相互作用来稳定。直接的分子动力学模拟在研究这些形态方面是不成功的，因为它们的形成与动力学障碍有关。在这项研究中，我们将在分子模拟中采用新的自由能估计策略来研究表面活性剂在一系列形状和尺寸的MNPs表面上的吸附形态的热力学稳定性。我们将开发罕见事件采样技术，以确定在与成核过程相关的时间尺度上形成这些形态所涉及的分子过程。最后，为了了解吸附形态如何影响MNPs的界面性质，我们将通过分子模拟研究表面活性剂介导的MNPs聚集。PI投资于几个与研究密切相关的教育目标。为了提高初高中学生对STEM领域的积极性和好奇心，PI计划开发一款基于教育策略的电脑游戏，要求玩家在模拟场景中做出工程和经济决策，包括使用表面活性剂来减少石油管道腐蚀。PI已经开发了软件的初始版本，并在最初一批学生身上进行了测试。PI将与当地一所高中密切合作，通过各种活动启发学生对STEM领域的认识，包括让学生参与STEM相关的讨论，并邀请他们参观俄亥俄大学的实验和计算研究小组。将开展教育外展活动，以吸引俄亥俄州阿巴拉契亚地区的成员。该项目将把该职业计划的研究内容纳入研究生和本科生的课程开发中，并将招收本科生，特别是那些来自代表性不足的部门的本科生进行研究。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。

Nanoparticles are approximately 1000 times smaller than the width of a human hair. Metallic nanoparticles have been found to be useful for many applications, such as for destroying cancer cells in our bodies, enhancing the imaging of human organs, catalyzing chemical reactions to reduce unwanted byproducts, improving the performance of paints and coatings, and fabricating nanoscale electronic devices and photovoltaic cell components. In each of these cases, nanoparticles of application-specific shape are required. Surfactants (soap-like substances) tend to attach strongly and pack densely on to metal surfaces. This enables the synthesis of metallic nanoparticles of a desired shape when surfactants are attached to specified surface regions of the growing nanocrystal to control the relative growth rates of its facets. Attached surfactants also influence how these nanoparticles cluster together to form ordered arrangements, a key enabler of nanomanufacturing processes. Currently, there are significant gaps in our understanding of surfactant/metallic nanoparticle interactions that have stymied progress in the envisioned applications. Part of the difficulty lies in the extremely small size of nanoparticles, putting the observation of many of the processes at work out of reach of experimental studies. Another challenge lies in the sheer number of factors that affect the attachment and packing of surfactants on metallic nanoparticles. In this work, we will use computer models to perform a systematic study of how surfactants of different chemical makeup attach to different faces of metallic nanoparticles. In this project, computer models will probe the behavior of the systems at the length-scale of a molecule, thus providing a detailed understanding of these dynamic processes, making it possible to optimize nanoparticle growth conditions for the desired applications. This research will be accompanied by a significant educational component. An educational strategy-based computer game will be created for middle and high school students to guide them towards STEM-based fields. Elements of the research will be incorporated in the teaching curriculum, and educational outreach activities will be performed to engage members of the Appalachian region of Ohio.The overall research objective of this CAREER project is to develop a fundamental understanding of the interactions between metallic nanoparticles (MNPs) and surfactant molecules in aqueous media using molecular simulation. MNPs have increasingly attracted interest owing to their unique electrical, thermal, and optical properties, and have found applications in bioimaging, drug delivery, molecular sensors, nanofabrication, photothermal therapy, and heterogeneous catalysis. These diverse technological applications often involve the interactions of MNPs with surfactants. Due to their strong affinity towards metal-water interfaces, surfactants adsorb at these interfaces in high-density ordered morphologies. These surface structures are stabilized by hydrophobic interactions between the alkyl tails of surfactants as well as the strong polar head-metal interactions. Straightforward molecular dynamics simulations have been unsuccessful in studying these morphologies because of the kinetic barriers associated with their formation. In this research, we will employ novel free energy estimation strategies in molecular simulation to study the thermodynamic stability of the adsorption morphologies of surfactants on the facets of MNPs in a range of shapes and sizes. We will develop rare-event sampling techniques to identify the molecular processes involved in the formation of these morphologies over timescales relevant to nucleation processes. Finally, to understand how the adsorption morphologies affect the interfacial properties of MNPs, we will study surfactant-mediated aggregation of MNPs via molecular simulations. The PI is invested in several educational objectives that are closely tied to the research. To increase motivation and curiosity among middle and high school students for the STEM fields, the PI plans to develop an educational strategy-based computer game which will require a player to make engineering and economic decisions in simulated scenarios, including the use of surfactants to reduce petroleum pipeline corrosion. The PI already has developed an initial version of the software and tested it on an initial cohort of students. The PI will work closely with a local high school to enlighten students about the STEM fields through various activities, including engaging the students in STEM-related discussions and inviting them to visit the experimental and computational research groups at Ohio University. Educational outreach activities will be performed to engage members of the Appalachian region of Ohio. The PI will incorporate aspects of the research stemming from this CAREER program into curriculum development at graduate and undergraduate levels, and will recruit undergraduate students, especially those from underrepresented sections, for research.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.