(649c) Physiochemical Properties of Functional Polymer / Solid Carbon Surface Composites Via Molecular Simulation

The discovery of new materials has introduced a fundamental paradigm shift in nanotechnology in numerous systems including micro/nano electromechanical systems (MEMS/NEMS) and efforts are being directed towards their applications by converging various functionalities. For example, graphene has recently attracted scientific/technological interest due to its exotic electric & thermo-mechanical properties, elasticity, low surface energy, and consequently low friction coefficient. Due to these superior physiochemical properties, graphene has recently been considered as the most promising candidate for high endurance materials applicable in MEMS/NEMS. However, at the nano-scale dimensions of these devices, the molecular mechanisms govern the system properties, and stringent confinement of the systems induced by composites of nano materials further complicate the experimental measurement of the physiochemical properties. Therefore, it is essential to develop a computational approach enabling molecular simulation for the interfacial phenomena of functional polymers and solid surfaces via controlling molecular architectures and external operation conditions of the integrated system.

In this study, we investigated the physiochemical properties of nano composites by combining various types of functional polymers and solid carbon surfaces (e.g., diamond, diamond-like carbon (DLC), and graphene) via large scale coarse-grained bead-spring molecular dynamics (MD) based on the endgroup-surface potential energy parameters determined by atomistic level theory [1, 2]. Intermolecular force fields between functional endgroups in polymers and carbon surfaces were atomistically estimated from the equilibrium geometries of truncated functional polymers and the models of the surface materials. By using MD, polymeric film conformations were characterized by anisotropic radii of gyration, where the perpendicular component determines the thickness of a monolayer film, and functional bead density defines the adhesion distribution of functional endgroups and the internal structure (e.g., layering and clustering) of the multilayer films. The dynamic responses were also investigated by calculating the self-diffusion coefficient of a tagged molecule. Various structures of functional polymers were utilized by tuning the polymer properties such as the functionalities (endgroup position and strength), molecular weight, and number of branches, where the star-like polymers with n branches (n=3 or 4) contain additional functional endgroups on the branches [3]. In summary, we focused on investigating the key parameters of nano composites governing the physiochemical properties by considering the functionality, the structures of polymers, and their interactions with the various carbon surfaces.

References

1. M.S. Jhon, R. Smith, S.H. Vemuri, P.S. Chung, D. Kim, and L.T. Biegler, “Hierarchical multiscale modeling method for head/disk interface,” IEEE Trans. Magn., 47, 87-93 (2011).
2. R. Smith, P.S. Chung, J.A. Steckel, M.S. Jhon, and L.T. Biegler, “Force field parameter estimation of functional perfluoropolyether lubricants,” J. Appl. Phys., 109, 7B728 (2011).
3. D. Shirakawa and K. Ohnishi, “A study on design and analysis of new lubricant for near contact recording,” IEEE Trans. Magn., 44, 3710 (2008).