AVS 60th International Symposium and Exhibition
    Tribology Focus Topic Monday Sessions
       Session TR+AS+NS+SS-MoA

Invited Paper TR+AS+NS+SS-MoA6
Chemical Origins of Interfacial Friction: Insights from Atomistic Simulations

Monday, October 28, 2013, 3:40 pm, Room 203 C

Session: Molecular Origins of Friction
Presenter: I. Szlufarska, University of Wisconsin-Madison
Authors: I. Szlufarska, University of Wisconsin-Madison
K. Huang, University of Wisconsin-Madison
Y. Liu, Massachusetts Institute of Technology
Correspondent: Click to Email
While interfacial chemistry plays a critical role in frictional response of materials, understanding chemical changes that occur in sliding mechanical contacts has been challenging. Experimentally, the difficulty lies in the limited ability to characterize contacts in situ and typically chemical characterization of interfaces is carried out before or after sliding. Modeling and simulations can provide powerful insights into the chemistry of frictional contacts, however models that possess a high level of chemical fidelity are often limited to small system sizes and short simulation time scales. Here, we overcome this limitation by bringing together complementary simulations methods that range from ab initio calculations based on the density functional theory (DFT), large scale molecular dynamics (MD) simulations with reactive empirical potentials, and the kinetic Monte Carlo (kMC) technique. In this talk we will discuss examples of how these methodologies have been used to identify chemical origins of friction. One example is the discovery of mechanisms that underlie aging of silica in aqueous environments, which is of interest for multiple phenomena ranging from wafer bonding to shallow tectonic earthquakes. We have demonstrated that in the absence of deformation creep, aging of silica takes place by formation of interfacial siloxane bridges. We have discovered a new mechanism for interaction between these bridges and have shown that this interaction is critical to explain experimentally observed logarithmic dependence of aging on time. In addition, we will discuss our newly develop theory that enables efficient and accurate calculations of friction at solid/liquid interfaces directly from MD simulations and that overcomes the typical time scale limitations of standard MD simulations. This theory has been validated for multiple types of surfaces and liquids and it can be used for design of chemical interfaces for applications in aqueous environments, such as nano- and micro-fluidics.