NER: Multi-timescale Molecular Simulation of Fluidity of Ultrathin Nanoconfined Aqueous Systems

Cummings，Peter T.范德比尔特大学“NER：超薄纳米限制水系统流动性的多时间尺度分子模拟。“纳米限制水系统的性质在粘土膨胀，生物润滑，生命系统中的电荷迁移以及微/纳米机电系统（M/NEMS）中的摩擦控制等领域具有相当大的兴趣和重要性，无论是天然的还是人造的。尽管在过去的几十年里，我们对固体表面附近液体物理学的理解，特别是在纳米级限制下，取得了重大进展，但很少有理论研究来研究纳米限制的缔合水膜的吸附结构和摩擦性能。要了解的摩擦动力学观察到的现象在表面力平衡（SFB）实验的两个云母表面之间的水化结合层，我们提出了一个纳米级的探索性研究（NER）项目，涉及到开发和应用“多时标”的分子模拟，包括SFB实验时标。该方法结合了一个现实的分子模型的复杂云母液体系统和混合模拟技术，结合微观分子松弛与宏观力学系统的动力学。传统的分子动力学和混合模拟技术将在该提案中进行探讨。此外，非平衡分子动力学（NEMD）的瞬态时间相关函数（TTCF）方法将被扩展到研究非常低的剪切速率，允许分子动力学，混合模拟结果和实验数据之间的直接比较。结合水化层的结构，界面动力学（分子的扩散性，水化鞘的流动性），和驱动云母板的宏观动力学的新的物理见解将出现。这些见解是迫切需要的，因为最近的研究结果可能的Pt纳米粒子污染的表面上的实验装置，和污染的潜在影响，已经抛出了怀疑的许多公认的实验结果在过去的十年。本项目拟开发的建模和模拟工具可在今后关于此类污染影响的辩论中发挥重要作用。建议的工作成果的智力价值从整合的努力，卡明斯，冷，和Delhommelle（谁将加入卡明斯组从2004年6月1日开始）与广泛的背景，在计算纳米科学，固体力学和纳米摩擦学，和NEMD。这些努力将极大地提高我们的理解的性质的水性液体在nanofinition。这将在理解自然界的微/纳米机电系统（M/NEMS）（例如，细菌中的鞭毛马达），并将提供深入了解合成M/NEMS的设计。拟议的研究的更广泛的影响，包括多时间尺度的分子模拟方法的发展，并使用真实的分子模型，以调查自然发生的环境中的纳米封闭的水系统。提出的混合分子模拟方法克服了传统分子动力学（MD）模拟中的时间尺度问题，并可应用于纳米压痕、原子力显微镜（AFM）和化学力显微镜（CFM）等纳米尺度过程，以及生命系统中生物分子的结合/解结合和地下油藏中石油的开采（能源提取）等。

Cummings, Peter T.Vanderbilt University"NER: Multi-timescale Molecular Simulation of Fluidity of Ultrathin Nanoconfined Aqueous Systems."The properties of nanoconfined aqueous system are of considerable interest and importance in areas as diverse as clay swelling, bio-lubrication, charge migration in living systems, and the friction control in micro/nano electro-mechanical systems (M/NEMS), both natural and man-made. Although significant progress toward our understanding of the physics of liquids in the vicinity of solid surfaces, and particularly under nanoscale confinement, has been made in the past few decades, very few theoretical studies have been conducted to investigate the adsorbed structure and frictional properties of nanoconfined associative aqueous films. To understand the frictional dynamics underlying the observed phenomena in surface force balance (SFB) experiments of hydration bound layers between two mica surfaces, we propose a nanoscale exploratory research (NER) project that involves the development and application of "multi-timescale" molecular simulations to encompass the SFB experimental timescales. The approach incorporates a realistic molecular model for complex mica-liquid system and a hybrid simulation technique that combines microscopic molecular relaxation with macroscopic dynamics of mechanical systems. Both conventional molecular dynamics and hybrid simulation techniques will be explored in the proposal. Moreover, the transient time correlation function (TTCF) method of non-equilibrium molecular dynamics (NEMD) will be extended to study very low shear rates, allowing a direct comparison between molecular dynamics, the hybrid simulation results and experimental data. New physical insights into the structure of bound hydration layers, the interfacial dynamics (diffusivity of molecules, fluidity of hydration sheath), and the macroscopic dynamics of the driven mica plate will emerge. These insights are urgently needed since recent findings of possible Pt nanoparticle contamination on the surfaces of the experimental apparatuses, and the potential impact of the contamination, have thrown doubt on much of the accepted experimental findings of the past decade. Modeling and simulation tools of the kind proposed for development in this project can play an essential role in the coming debate over the impact of such contamination. The intellectual merit of the proposed work results from integrating the efforts of Cummings, Leng, and Delhommelle (who will join Cummings group beginning from June 1, 2004) with extensive backgrounds in computational nanoscience, solid mechanics and nanotribology, and NEMD. These efforts will greatly enhance our understanding of the properties of aqueous liquids in nanoconfinement. This will play a key role in the understanding nature's micro/nano electro-mechanical systems (M/NEMS) (e.g., flagellar motors in bacteria) and will provide insight into the design of synthetic M/NEMS. The broader impacts of the proposed research include the development of multi-timescale molecular simulation methodology and using the real molecular model to investigate nanoconfined aqueous system in naturally occurring environment. The hybrid molecular simulation method proposed will overcome the timescale issue encountered in conventional molecular dynamics (MD) simulations, and can be applied to other nanoscale processes, such as nanoindentation, atomic force microscopy (AFM) and chemical force microscopy (CFM), and binding/unbinding bio-molecules in living systems, as well as recovery of petroleum from underground reservoirs (energy extraction), etc.