Molecular Dynamic Assessment of Carbon Nanotube Drag In Physiologic Conditions

描述（由申请人提供）：碳纳米管（CNT）的日益普及引起了人们对超细颗粒（特别是人造纳米材料）潜在的人类健康和环境影响的严重关注。为此，虽然进行了重要的研究，以确定纳米管的材料毒性和它们的潜力，例如，刺激肺纤维化，气溶胶动力学模拟工具可以作为一个有价值的补充资产，以调查之间的联系的呼吸流量，随之而来的动态纳米管在呼吸道，并最终沉积的碳纳米管的呼吸系统壁。这种分析的典型结果将是对各种尺寸和类型的CNT在生理流动条件下在呼吸道中渗透的深度以及浓度水平和分布的估计。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。纳米尺度下的主导力是阻力和布朗运动，其中前者是本提案的重点。的长度尺度的数量级分析表明，取决于CNT的大小和取向相对于自由的，可能有两个流动制度的相关CNT阻力-自由分子和过渡。然而，文献回顾显示，在这些流动制度的纳米管的阻力公式的情况下。为了解决这一关键和未满足的CNT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CNT上的气流进行一系列分子动力学模拟，并获得CNT上的阻力作为呼吸道相对湿度的函数;流速;倾斜度 CNT相对于流向方向的角度;以及CNT直径、手性、纵横比和端部效应。模拟数据将被分析并简化为阻力系数函数。研究结果将在一个与气溶胶有关的会议上发表，随后提交给（气溶胶）期刊发表，以便使阻力系数函数可供更广泛的科学界使用;从而使未来的气溶胶动力学模拟CNT在干燥或潮湿空气中的流动。

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.