Molecular Dynamic Assessment of Carbon Nanotube Drag In Physiologic Conditions

描述（由申请人提供）：碳纳米管（CNTs）的日益普及引起了人们对超细颗粒，特别是人造纳米材料对人类健康和环境的潜在影响的严重关注。为此，虽然进行了重要的研究以确定纳米管的物质毒性及其潜力，例如，刺激肺纤维化，但气溶胶动力学模拟工具可以作为有价值的补充资产，用于研究呼吸流动、随后的呼吸道纳米管动力学以及最终在呼吸系统壁上沉积的碳纳米管之间的联系。这种分析的典型结果是估计在生理流动条件下，各种大小和类型的碳纳米管在呼吸道中渗透的深度、浓度水平和分布。成功的纳米管动力学模拟的核心在于纳米管所经历的力的精确模型的可用性。纳米尺度上的主导力是阻力和布朗运动，其中前者是本提案的重点。长度尺度的数量级分析表明，根据碳纳米管相对于自由流的大小和方向，可能有两种与碳纳米管相关的流动形式——无阻力分子和过渡。然而，对文献的回顾揭示了纳米管在这些流动状态下的阻力公式的缺失。为了解决这一关键且未满足的碳纳米管动力学建模需求，本项目提出的具体目标是在生理现实条件下对碳纳米管上的空气流动进行一系列分子动力学模拟，并获得碳纳米管上的阻力作为呼吸道相对湿度的函数；流量；的倾向

DESCRIPTION (provided by applicant): The growing ubiquity of carbon nanotubes (CNTs) has raised serious concerns about the potential human health and environmental implications of ultrafine particles in general, and manufactured nanomaterials in particular. To this end, while significant research is conducted to ascertain the material toxicity of nanotubes and their potential, for example, to stimulate pulmonary fibrogenesis, aerosol dynamics simulation tools can serve as a valuable complementary asset to investigate the link between the respiratory flow, the ensuing dynamics of nanotubes in the respiratory tracts, and the eventual deposition of CNTs on the respiratory system walls. A typical outcome of such an analysis would be an estimate of how deep, and at what concentration levels and distributions, CNTs of various sizes and types would penetrate in the respiratory tract under physiologic flow conditions. At the heart of a successful nanotube dynamics simulation lies the availability of accurate models for forces experienced by the nanotube. The dominant forces in the nanometer scale are drag and Brownian motion, where the former is the focus of this proposal. An order of magnitude analysis of the length scales reveals that, depending on the size and orientation of the CNT with respect to the freestream, there may be two flow regimes of relevance to CNT drag - free-molecule and transition. Yet, a review of the literature reveals an absence of drag formulae for nanotubes in these flow regimes. To address this critical and unmet CNT dynamics modeling need, the Specific Aim proposed for this project is to perform a series of Molecular Dynamics simulations of air flow over CNTs under physiologically realistic conditions, and to obtain the drag on the CNT as a function of the relative humidity of the respiratory tract; the flow rate; the inclination angle of the CNT with respect to the streamwise direction; as well as the CNT diameter, chirality, aspect ratio, and end effects. The simulation data will be analyzed and reduced into a drag coefficient function. The results will be presented at an aerosol-related conference and subsequently submitted to (aerosol) journals for publication so as to make the drag coefficient function available to the wider scientific community; thereby, enabling future aerosol dynamics simulations of CNT flow in dry or moist air. PUBLIC HEALTH RELEVANCE: The ability to accurately predict the transport and deposition details of carbon nanotubes in the human respiratory tract can be of significant benefit to making successful toxicologic impact assessments, establishing appropriate environmental standards, and determining safe exposure limits. The capability to make such predictions hinges, as a minimum, on the availability of accurate drag coefficients for carbon nanotubes under physiologically correct flow conditions. Yet, such drag coefficient data for nanotubes are absent in the literature. The objective of this research is to fill this critical gap, and to develp drag coefficient data using results from a series of simulations, which will be conducted during the project.