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

在水环境中，在两个分子光滑的固体表面之间以纳米级距离诱导的力在许多不同的系统中普遍存在，其潜在的机制是许多拟议技术的核心。在这个拟议的项目中，PI将进行一项基础的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：稠密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。将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许多技术应用至关重要，从微/纳米机电系统(MEMS/NEMS)中的摩擦和润滑以及生物界面上的生物溶解，到离子通道中的纳米流体(或通过拥挤的细胞内环境)和蛋白质折叠。研究目标包括：(1)发展一种分子模拟方法，结合纳米承压水体系中表面-水-离子络合物的真实分子模型和机械分子系综来描述表面力装置(SFA)实验中的真实情况；(2)基础研究亲水表面之间的水合力、疏水表面之间的去湿、疏水吸引和坍塌；以及(3)纳米尺度表面接近和剪切的多时间尺度混合分子模拟，结合适用于低剪切速率的瞬时时间关联函数(TTCF)形式。这项拟议工作的学术价值在于它的目标是在分子水平上阐明纳米受限水体系的水合力、疏水相互作用和剪切动力学的潜在机制，整合Leng和Cummings的互补专业知识，并协调雅各布·克莱因小组的理论研究和实验研究。拟议的研究的更广泛的影响在于它增强了我们在理解与SFA实验中观察到的水合力和疏水效应有关的长期基本问题方面的知识。该研究计划的新发现将通过出版物、会议报告和网站传达给SFA科学界，并将用于指导生物溶解和生物MEMS/NEMS器件的工程设计。这些发现还将对理解蛋白质折叠、自组装和生物学中的纳米力学产生潜在的影响。一名博士生将通过这个项目接受培训。本科生将参加这个由范德比尔特大学夏季本科生研究项目资助的跨学科研究项目。此外，K-12教师将有机会通过范德比尔特教师暑期研究体验计划参与该项目。PI和共同PI将在化学工程研究生分子模拟课程、初级机械工程动力学课程(ME190，由PI授课)和ES101机械工程前沿课程(ES101，机械工程前沿)中提供基于这项研究工作的讲座，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.