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.
