(420o) The Rheological Responses of Binary Blended Perfluoropolyether Nano Film

During the intermittent contact between the head and the disk of the hard disk drive, the perfluoropolyether (PFPE) lubricant, which prevents tribological and mechanical damage causing from the direct head-disk contact, experiences the shear/elongation deformation and flow. Since the head media spacing, which represents the spacing between read/write head and the magnetic media in the hard disk drive (HDD), is decreasing less than 6.5 nm for Tbits/in² level HDDs [1], the total contact time also increases. Therefore, the molecular rheology of PFPE become critically important in designing effective lubricants that control the friction and wear. Recently, it was found that the application of nano blend PFPE film becomes one of the promising alternatives to enhance the performance and reliability [2]. In this paper, we examine for the first time the rheological responses of nano blend PFPE including dynamic moduli and complex viscosity, by monitoring the time-dependent strain-stress plots via nonequilibrium molecular dynamics (MD) simulations [3]. We observed that pure nonfunctional PFPEs exhibit liquid-like behavior, while “pseudoreptation-like” or “agglomeration” behavior was observed for the pure functional PFPEs, similar to our previous findings [4]. In addition endgroup couplings due to strong functional endgroup weaken as the temperature increases. For the binary blend PFPEs, we also observed “pseudoreptation-like” or agglomeration phenomena, which depend strongly on the blend ratio and imposed condition (e.g., temperature and oscillatory frequency). We established finger print analysis between G¢-G² and nanoblend ratio. By constructing modified Cole-Cole plot [5] (i.e., relationship between storage and loss moduli), we found that the nanostructural conformation depends on the blend ratio at low frequency, while weakly depends at high frequency. By analyzing the nano blend PFPE relaxation processes, the results provide us the optimization parameters of nano rheology of lubricant selection criteria to enhance the HDD performance.

References

1. J. Gui, “Tribology challenges for head-disk interface toward 1 Tb/in²,” IEEE Trans. Magn., 39, 716 (2003).
2. P.S. Chung, H. Park, and M.S. Jhon, “The static and dynamic responses of binary mixture perfluoropolyether lubricant films – Molecular structural effects,” IEEE Trans. Magn., 45, 4644 (2009).
3. Q. Guo, P.S. Chung, H.G. Chen, and M.S. Jhon, “Molecular rheology of perfluoropolyether lubricant via nonequilibrium molecular dynamics simulation,” J. Appl. Phys., 99,  08N105 (2006).
4. Q. Guo and M.S. Jhon, “The viscoelastic behavior of perfluoropolyether lubricants,” IEEE Trans. Magn., 42, 2540 (2006).
5. M.S. Jhon, “Physicochemical properties of nanostructured perfluoropolyether films,” Adv. Chem. Phys., 129,  1 (2004).