EAGER: Collaborative Research: Dynamics of Nanoparticles in Light-Excited Supercavitation

可以通过液体高速推进的纳米粒子(称为纳米微球)可以在靶向药物输送、原位诊断和纳米制造等应用中发挥重要作用。对于这种应用，控制高速纳米微米的方向是至关重要的。然而，高速纳米切割器大多是由随机方向的力推动的，而制导式纳米切割器目前仅限于低速。因此，设计完全可控但移动迅速的纳米微米具有巨大的技术潜力。最近的实验观察到，极快的(100,000微米/S)金纳米粒子游泳者可以被光作为外部能源引导。然而，其潜在的机制尚不完全清楚。这个急切的项目将通过研究光驱动的纳米粒子的力和能量平衡，向理解这一现象迈出第一步。通过实验和数值模拟的结合，我们将对纳米振动的动力学有一个基本的了解，并解决有关其运动的潜在机制的问题。这反过来将提供新的信息，可以导致广泛的先进纳米工程应用，例如选择性地在表面打印纳米结构以用于传感应用，或者使用皮肤可穿透的近红外光源将携带药物的纳米微球输送到皮肤下的生物细胞。观察到的超快纳米微米的运动从未被报道过，也不能用斯托克斯定律来解释。这个急切的项目将研究一种假设，即当纳米粒子被表面等离子体共振(SPR)峰处的光激发时，粒子周围会形成纳米级的气泡(即超空化)。这提供了一个近乎无摩擦的环境，使其能够高速移动，前提是气泡能够保持完好。该项目的目标是通过使用多尺度建模和实验技术分析纳米粒子在超空泡内移动时所经历的力(光学力和流体力)来验证这一假设。这个项目由两项任务组成。首先，将进行多尺度建模，以了解纳米粒子在超空泡中的动力学。其次，通过实验观察纳米悬浮体的动力学过程，并验证计算结果。这个项目将揭开涉及纳米光子光学力、光热超空化和纳米尺度热流体的耦合效应的基本物理。这项工作的一个重要方面将是将研究与教育相结合，并培训多学科领域的下一代科学家和工程师，这对美国的技术密集型行业至关重要。我们将教育圣母大学的研究生和科罗拉多梅萨大学(CM)的本科生研究人员，CM是一个主要为本科生服务的机构，服务于近10,000名学生，包括许多农村学生、第一代学生、非传统学生(单亲、退伍军人和返校学生)、西班牙裔和其他在STEM学科中代表性较低的学生群体。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。

Nanoparticles that can be propelled through liquids at high speed (called "nanoswimmers") can play important roles in applications such as targeted-drug delivery, in-situ diagnostics and nanofabrication. For such applications, controlling the direction of high-speed nanoswimmers is critical. However, high-speed nanoswimmers are mostly propelled by forces with random directions, and guided nanoswimmers are currently limited to slow speeds. Designing fully controllable yet fast-moving nanoswimmers thus has significant technological potential. Recent experiments have observed that extremely fast ( 100,000 micron/s) gold nanoparticle swimmers can be directed by light as an external energy source. However, the underlying mechanism is yet to be fully understood. This EAGER project will take the first step toward understanding this phenomenon by studying the force and energy balance of a nanoparticle driven by light. A combination of experiments and numerical simulations of the motion of the nanoswimmers will provide a basic understanding the dynamics of nanoswimmers and resolve questions about the underlying mechanisms of their motion. This, in turn, will provide new information that can lead to a wide range of advanced nanoengineering applications, such as selectively printing nanostructures at a surface for sensing applications or delivering drug-carrying nanoswimmers to biological cells under the skin using skin-penetrable near infrared light sources.The observed ultra-fast nanoswimmer motion has never been reported and could not be explained by Stokes law. This EAGER project will investigate a hypothesis that when the nanoparticle is excited by the light at the surface plasmon resonance (SPR) peak, a nanoscale bubble forms surrounding the particle (i.e., super-cavitation). This provides a near frictionless environment that allows it move at high speed, provided the bubble can remain intact. The objective of the project is to test this hypothesis by analyzing the forces (optical force and fluidic force) the nanoparticle experiences when moving inside the supercavitation bubble using multiscale modeling and experimental techniques. This project consists of two tasks. First, multi-scale modeling will be conducted to understand the nanoparticle dynamics in supercavitation. Second, experiments will be conducted to observe the nanoswimmer dynamics and validate the computation results. This project will unravel fundamental physics involving coupled effects of nanophotonic optical forces, optothermal super-cavitation, and nanoscale thermo-fluids. An essential aspect of this work will be the integration of research with education and training of the next generation of scientists and engineers in multi-disciplinary fields, which are crucial for the technology-intensive U.S. industries. We will educate graduate students at Notre Dame and undergraduate researchers at the Colorado Mesa University (CM), a Primarily Undergraduate Institution serving nearly 10,000 students including many rural, first-generation, non-traditional (single parents, veterans and returning students), Hispanic, and other student groups underrepresented in STEM disciplines.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.