Multi-Timescale Molecular Simulation Study of Hydration Force, Hydrophobic Interaction and Shear Dynamics in Nanometer Confined Aqueous Systems

在水环境中，两个分子光滑的固体表面之间以纳米尺度的距离诱导的力在许多不同的系统中是普遍存在的，并且潜在的机制是许多提出的技术的核心。在这个拟议的项目中，PI将进行一项基础和创新的分子模拟研究，以探索这些力的潜在机制，这些力可以分为两大类：密集电解质溶液中两个亲水表面之间的短程排斥水合力和水中两个疏水表面之间的长程疏水吸引力。发展一种多时间尺度的混合分子模拟方法来研究纳米尺度的方法和两个表面之间的剪切。了解这些物理现象对于许多技术应用至关重要，从微/纳机电系统（MEMS/NEMS）中的摩擦和润滑以及生物界面的生物润滑，到离子通道（或通过拥挤的细胞内环境）中的纳米流体和蛋白质折叠。研究目标包括：（1）发展了一种分子模拟方法，该方法结合了纳米受限水体系中表面-水-离子复合物的真实分子模型和机械分子系综，以代表表面力装置（SFA）实验中的真实的情况;（2）对亲水表面之间的水合力、疏水表面之间的去湿、疏水吸引和塌陷的潜在机制进行了基础研究;（3）结合适用于低剪切速率下的瞬态时间相关函数（TTCF）形式，对纳米尺度表面接近和剪切进行了多时间尺度混合分子模拟研究。拟议的工作的智力价值在于其目标是阐明，在分子水平上，水化力，疏水相互作用和剪切动力学的纳米限制水系统的基本机制，整合冷和卡明斯的互补专业知识，并协调理论研究与实验研究在雅各布克莱因的小组。拟议研究的更广泛影响在于它增强了我们对SFA实验中观察到的水合力和疏水效应相关的长期基本问题的理解。研究计划的新发现将通过出版物，会议演示和网站传达给SFA科学界，并将用于指导生物润滑和bioMEMS/NEMS设备的工程设计。这些发现也将对生物学中蛋白质折叠，自组装和纳米力学的理解产生潜在的影响。一名博士生将通过该项目接受培训。本科生将参加这个跨学科的研究计划，由范德比尔特夏季本科研究计划资助。此外，K-12教师将有机会通过范德比尔特夏季教师研究经验项目参与该项目。PI和co-PI将在化学工程研究生分子模拟课程和初级机械工程动力学课程中提供基于本研究工作的见解的讲座（ME 190，由PI教授），以及ES 101，机械工程前沿，为机械工程专业大一新生开设的入门课程，旨在激发他们对机械工程前沿研究领域的兴趣。

The forces induced between two molecularly smooth solid surfaces at nanometer scale distances in an aqueous environment are ubiquitous in many diverse systems, and the underlying mechanism is at the heart of numerous proposed technologies. In this proposed project, the PIs will carry out a fundamental and innovative molecular simulation study to explore the underlying mechanisms of these forces, which can be classified into two main categories: The short-range repulsive hydration force between two hydrophilic surfaces in dense electrolyte solutions and the long-range hydrophobic attraction force between two hydrophobic surfaces in water. A multi-timescale hybrid molecular simulation method will be developed to investigate the nanoscale approach and shearing between two surfaces. Understanding these physical phenomena is critical to many technological applications, ranging from friction and lubrication in micro/nano electro-mechanical systems (MEMS/NEMS) and biolubrication at biological interfaces, to nanofluidics in ion channels (or through crowded intracellular environments) and protein folding. The research objectives include: (1) Development of a molecular simulation methodology that incorporates realistic molecular models for the surface-water-ion complex in nanoconfined aqueous system and mechanomolecular ensembles to represent the real situation in surface force apparatus (SFA) experiments; (2) Fundamental studies of the underlying mechanisms of hydration force between hydrophilic surfaces, the dewetting, hydrophobic attraction and collapse between hydrophobic surfaces; and (3) Multi-timescale hybrid molecular simulation study of nanoscale surface approach and shearing, combined with the transient time correlation function (TTCF) formalism applicable at low shear rates. The intellectual merit of the proposed work lies in its goals to elucidate, at molecular level, the underlying mechanisms of hydration forces, hydrophobic interaction and shear dynamics of nanometer confined aqueous systems, to integrate the complementary expertise of Leng and Cummings, and to coordinate the theoretical studies with experimental studies in Jacob Klein's group. The broader impacts of the proposed research lie in its enhancement of our knowledge in understanding the long-standing fundamental questions related to the hydration force and hydrophobic effects observed in SFA experiments. The new findings from the research program will be communicated to SFA science community via publication, conference presentation and website, and will be used to guide the engineering design for biolubrication and bioMEMS/NEMS devices. These findings will also have potential impact on the understanding of protein folding, self-assembly, and nanomechanics in biology. One PhD student will be trained through this project. Undergraduate students will participate in this interdisciplinary research program, funded by the Vanderbilt Summer Undergraduate Research Program. Further, K-12 teachers will have the opportunity to participate in the project through Vanderbilt Summer Research Experience for Teachers programs. The PI and co-PI will offer lectures based on the insights derived from this research work in a chemical engineering graduate molecular simulation course, in the junior-level mechanical engineering dynamics course (ME190, being taught by the PI), and in ES101, Frontiers in Mechanical Engineering, an introductory course for freshmen mechanical engineering students designed to excite their interest in frontier research areas in mechanical engineering.