(601e) Interfacial Thermodynamics, Structure, and Dynamics of Imidazolium-Based Ionic Liquid-Oil Lubricants Under Confinement: Role of Surface Nano-Roughness and Temperature | AIChE

(601e) Interfacial Thermodynamics, Structure, and Dynamics of Imidazolium-Based Ionic Liquid-Oil Lubricants Under Confinement: Role of Surface Nano-Roughness and Temperature

Authors 

Lazarenko, D. - Presenter, The University of Akron
Khabaz, F., The University of Akron
While the machinery industry grows rapidly, it still accounts for losses due to wear of interacting components as for relying on conventional lubricants with only acceptable reduction of friction. A new generation of lubricants with superior tribological and thermophysical properties must be developed to significantly reduce friction and wear and increase the durability of rolling and sliding machinery. One of the proposed solutions to this problem is the addition of ionic liquid (IL)-based additives to conventional oils. ILs show unique properties such as low degree of toxicity, nonflammability, and thermal stability while exhibiting attractive rheological viscosity-temperature behavior. Hence, the lubricant, which contains IL, gains advanced rheological properties without dramatic altering of the existing lubricant production process. In this study, large-scale all-atom molecular dynamics simulations will be utilized to characterize the structural, dynamic, and interfacial thermodynamic properties of the imidazolium-based ILs mixed with hexadecane (as the base oil) near an iron surface to reveal the thermodynamic mechanism behind the multilayer structure formation on the solid surface, which potentially impacts the flow behavior. In the first step, we will study the effect of nanoconfinement on the density profile of the oil-IL mixture in the normal direction to the interface. Furthermore, the orientation of the molecules adsorbed at the interface will be studied at different degrees of surface nano-roughness and temperatures. In addition to the structural properties of the system, the dynamics of the molecules in both bulk and at the interface will be studied. Then the diffusion coefficient and density correlation functions will be explored as a measure of the dynamic properties of the mixture. The orientational properties of IL layers at the interface will be studied to quantify the ordering of ILs and how it will further influence the free energy of adsorption. Finally, the adsorption free energy of ILs at the metal interface will be determined using the umbrella sampling technique. These properties will be compared with those obtained from oil-metal surface calculations. Our preliminary results demonstrate that ILs are adsorbed on the surface of the metal and form ordered multilayer structures. These structures correspond to the most stable configuration of the oil-IL-metal system. Therefore, at the equilibrium conditions, the dynamics of lubricant molecules show a bimodal distribution corresponding to the bulk and interfacial regimes. The outcome of this work will elucidate the linkage between interfacial properties of the IL-oil lubricant on the metal surface and the physical properties of the surface and temperature. Results will help to select ion pairs that can potentially impact the rheological and tribological performance of the lubricant in a positive direction.