Effects of Molecular Structure on the Conformation and Dynamics of Perfluoropolyether Nanofilms

Chen, Haigang; Guo, Qian

doi:10.1109/tmag.2007.893639

Cited by 33 publications

(19 citation statements)

References 7 publications

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“…In the present study, the single PFPE molecule is considered to be a linear freely jointed chain consisting of N p beads, each with a mass of m. [2,[7][8][9] Each bead, including backbone beads (bb) and endbeads (eb), has a dispersive pairwise interaction as described by the truncated-shifted LennardJones (LJ) potential, U LP (r bb ):…”

Section: Simulationmentioning

confidence: 99%

Nano‐Rheology of Single Unentangled Polymeric Lubricant Films

Guo

Chung

Jhon

et al. 2008

Macro Theory & Simulations

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Rheology and tribology become more and more critical issues in order to satisfy the harsh requirements for ultra‐small head/media spacing HDDs. In this communication, MD simulations with a bead/spring model were employed to examine the nano‐rheological response of nonfunctional and functional PFPEs by analyzing the shear viscosity of nanoscale PFPE films and the relaxation processes as a function of wall interaction/separation and endgroup functionality. Our simulation results indicate that thin PFPE films show more solid‐like behavior, especially under high shear rate. The film deformation and shear viscosity change by tuning the film thickness and the endgroup functionality was discussed in conjunction with the relaxation processes.

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Section: Simulationmentioning

confidence: 99%

Nano‐Rheology of Single Unentangled Polymeric Lubricant Films

Guo

Chung

Jhon

et al. 2008

Macro Theory & Simulations

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“…This may result in changing lubricant surface morphology or lubricant transfer from the disk to the recording head. Coarse-grained bead spring (CGBS) molecular dynamics models [10][11][12][13][14][15][16][17][18][19][20][21][22] have been used to study the nanoscale dynamics of lubricant spreading. Researchers found that lubricant mobility decreases with increasing bonded ratio, 11 similar to what has been observed in experiments.…”

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confidence: 99%

Quantifying lubricant droplet spreading on a flat substrate using molecular dynamics

Noble

Ovcharenko

Raeymaekers

2014

Applied Physics Letters

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Understanding the physical behavior of polymer-based lubricants on the nanoscale is of critical importance to a myriad of engineering applications and devices. We have used molecular dynamics simulations to quantitatively evaluate the physical mechanisms underlying perfluoropolyether lubricant spreading on a solid substrate. We quantify the effect of molecular mass, molecule length, and lubricant and substrate functional end groups on lubricant spreading. The results show that lubricant functional end groups play a critical role in lubricant spreading on the nanoscale. Lubricant spreading increases with increasing molecule length for lubricant with functional end groups, but decreases with the increase in molecule length for lubricant without functional end groups. In the former case, the fraction of the lubricant chain that is functional is the primary driving factor for lubricant spreading, while in the latter case, the molecular mass is most important. For both lubricants with and without functional end groups, spreading is inhibited by molecule entanglement beyond a critical molecule length, and spreading becomes independent of lubricant functional end groups and molecular mass.

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“…This fit is only limited to the "tension" process as indicated by the blue symbols in Figs. 6 and 7 (4) Here, "0" stands for the reference point, where two films are completely merged into one confined film before the repulsion occurs inside the film.…”

Section: Resultsmentioning

confidence: 99%

“…Based on our previous study [4]- [8], PFPE molecules are characterized by the coarse-grained, bead-spring model, which neglects the detailed atomistic information while it keeps the essence of molecular structure. Solid surfaces that confine the PFPE film are assumed perfectly flat and structureless.…”

Section: Molecular Dynamicsmentioning

confidence: 99%

Nano-Mechanics of Perfluoropolyether Films: Compression Versus Tension

Guo

Chung

2008

IEEE Trans. Magn.

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As the head-disk spacing decreases, the contact mechanics between the head and disk becomes one of the critical issues for the head-disk tribology integration. In this paper, molecular dynamics (MD) is employed to simulate the nano-mechanics (i.e., "compression" and "tension") of confined molecularly thin perfluoropolyether (PFPE) films to examine the contact tribology fundamentals. For the "compression" process, functional PFPE demonstrates slightly higher clearance than nonfunctional PFPE; while during the "tension" process, an apparent fluid bridge was observed for functional PFPE. The normal stress profiles were calculated for both "compression" and "tension" processes, where the hysteresis phenomenon indicates the irreversible nature of functional PFPE nano-mechanics. N-modes Maxwell model was then further introduced to analyze the nano-mechanics relaxation process, suggesting that a second relaxation mode in the two-mode Maxwell model was induced by functional endgroups.

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Effects of Molecular Structure on the Conformation and Dynamics of Perfluoropolyether Nanofilms

Cited by 33 publications

References 7 publications

Nano‐Rheology of Single Unentangled Polymeric Lubricant Films

Nano‐Rheology of Single Unentangled Polymeric Lubricant Films

Quantifying lubricant droplet spreading on a flat substrate using molecular dynamics

Nano-Mechanics of Perfluoropolyether Films: Compression Versus Tension

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