(400d) A Peculiar Layering Structure and Transport Phenomenon of Nano-Blended Perfluoropolyether Thin Films

As polymeric thin film systems have been developed possessing molecularly thin configuration with enhanced protective and coating abilities, understanding the molecular structures and dynamic properties of functional polymeric films become important factors to discover high performance thin film. We experimentally and theoretically investigated spreading characteristics of functional / non-functional nanoscale thickness film made of the single component as well as binary blend perfluoropolyether (PFPE) derivatives [1]. By using optical surface analyzer (OSA), we observed spreading evolves with time in classical diffusive manner for nonfunctional PFPE Z, while functional PFPE Ztetraol exhibits “layering” structure with characteristic “shoulder” above the leading edge for single components system [2]. For binary blended film with Z and Ztetraol, results exhibit ultra-thin layering structure at the spreading edge with rapid proceeding and Ztetraol forms bonded layer inside the thin film. The qualitative molecular modeling results and description explaining the characteristics of the single component film as well as the peculiar behavior found in the nano blended films will be given.

To physically explain the layering structure and spreading mechanism of binary blend, we investigated the spreading of nonfunctional / functional blend thin film via molecular dynamics simulation. We found thin spreading edge consists of nonfunctional PFPE migrated from the top layer and the complex entanglement of nonfunctional / functional PFPE molecules inside the film, while the bottom layer is composed of bonded functional PFPE molecules as observed in the experiment. Since the spreading edge of binary mixture evolves rapidly enough, spatially dependent diffusion coefficients were calculated to examine the endgroup functionality and film conformation effect on the binary film spreading. It was found that the diffusivity of binary blend has same order as the nonfunctional PFPE, yet the spreading was retarded due to the entanglement in the binary nano film.

References:

[1] P.S. Chung, H. Chen, and M.S. Jhon, “Molecular dynamics simulation of binary mixture lubricant films,” J. Appl. Phys., Vol. 103, No. 07F526, 2008.

[2] Q. Guo, L. Li, Y.-T. Hsia, and M.S. Jhon, “A spreading study of lubricant films via optical surface analyzer and molecular dynamics,” IEEE Trans. Magn., Vol. 42, No. 10, pp. 2528, 2006.