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Journal Article 
Rheological Properties of PFPE Lubricants at Elevated Temperatures 
Chung, PilS; Song, W; Biegler, LT; Jhon, MS 
I E E E Transactions on Magnetics
ISSN: 0018-9464 
During the intermittent contact between the head and the disk of the hard disk drive (HDD), the perfluoropolyether (PFPE) lubricant experiences shear/ elongation deformation. Therefore, the molecular rheology of PFPE becomes critically important in designing optimal lubricants that control the friction and wear. In this paper, we examine, for the first time, the rheological responses of nanoblended PFPEs, including storage and loss moduli (G' and G ''), by monitoring the time-dependent stress-strain relationship via nonequilibrium molecular dynamics simulations. We observed that the nonfunctional PFPEs (Fomblin Z-type) exhibit liquid-like behavior, while agglomeration behavior was observed for the functional PFPEs (Fomblin Zdol-type). In addition, strong endgroup couplings due to functional endgroup weaken as the temperature increases. For binary blended PFPEs, we also observed similar phenomena, which strongly depends on the blend ratio and imposed condition (e.g., temperature and oscillatory frequency). We established a finger print analysis via G'-G '' plots for different blend ratios and temperatures. By analyzing the blended PFPE relaxation processes, our results provide the optimal parameters for lubricant selection criteria to enhance the HDD performance. 
Binary blends; Cole-Cole plot; nonequilibrium molecular dynamics (NEMD); perfluoropolyethers (PFPEs); rheology 
• ^Per- and Polyfluoroalkyl Substances (PFAS)
     PFPeS (2706-91-4)
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