First-Principles Insights into the Structural and Electronic Properties of Polytetrafluoroethylene in Its High-Pressure Phase (Form III)

Fatti, Giulio; Righi, Maria Clelia; Dini, Daniele; Ciniero, Alessandra

doi:10.1021/acs.jpcc.8b11631

Cited by 11 publications

(10 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It can be seen that the band structures of the three surfaces are almost identical and extremely similar to the band structure of the bulk (see Figure 2 in Ref. 42 ), also, the value of the band gap remains unaltered: ∆E gap = 5 eV. The calculated gap value is lower when compared to previous Hartree-Fock studies (∆E gap ∼ 8 eV) 31 and experimental measurements (∆E gap ∼ 10 eV).…”

Section: Resultssupporting

confidence: 73%

“…The chosen lattice parameters a = 8.70 Å, b = 5.97 Å, with a setting angle α = 37/38 • , were obtained in our previous study on the bulk properties of PTFE42 , and they are in good agreement with the experimental values a exp = 8.73 Å26 , b exp = 5.69 Å26 , and α exp = 35 • 34 .…”

supporting

confidence: 73%

“…The dispersion term was introduced by using the semiempirical Grimme method . The scaling parameter of the Grimme correction was tuned to a value of 0.42 to reproduce a cohesive energy density consistent with the experimental values . The ionic species are described by ultrasoft pseudopotentials (PP’s).…”

Section: Computational Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Ab Initio Study of Polytetrafluoroethylene Defluorination for Tribocharging Applications

Fatti

Righi

Dini

et al. 2020

ACS Appl. Polym. Mater.

Self Cite

View full text Add to dashboard Cite

Polytetrafluoroetyhlene (PTFE) is one of the most efficient polymers for green energy-harvesting devices like triboelectric nanogenerators because of its high capability of acquiring and retaining negative charge. Despite its extensive use, the relation between PTFE triboelectric behavior and its electronic properties has never been analyzed. To shed light on this important feature we have studied the electronic properties of PTFE low-index surfaces in the high pressure phase by means of density functional theory. We start by showing that adding either a positive or a negative charge on pristine surfaces is energetically unfavorable. We then demonstrate the role played by surface defects. When a surface fluorine vacancy is introduced the analysis of the band structure reveals that the defect generates a trap state that enables the surface to acquire and retain negative charge.

show abstract

Section: Resultssupporting

confidence: 73%

supporting

confidence: 73%

See 1 more Smart Citation

Ab Initio Study of Polytetrafluoroethylene Defluorination for Tribocharging Applications

Fatti

Righi

Dini

et al. 2020

ACS Appl. Polym. Mater.

Self Cite

View full text Add to dashboard Cite

show abstract

“…For instance, material stress can cause bond scission that results in a rearrangement of the charge of the surface and the release of ions and electrons [1]. The importance of tribocharging has led to the development of new nanoscale techniques and theoretical analysis [2] to study this phenomenon and to better understand its fundamental mechanisms. In industry, tribocharging is employed in many applications including sliding [3] and dry bearings [4], pharmaceutical [5,6], space [7] and green energy harvesting [8,9] and it has the potential to be at the forefront of technological innovations.…”

Section: Introductionmentioning

confidence: 99%

A Combined Experimental and Theoretical Study on the Mechanisms Behind Tribocharging Phenomenon and the Influence of Triboemission

et al. 2019

Self Cite

View full text Add to dashboard Cite

This work describes recent research into the mechanisms behind tribocharging and the influence of triboemission. The term tribocharging is a type of contact-induced electrification and refers to the transfer of charge between rubbing components. The term triboemission, on the other hand, refers to emission of electrons, ions and photons generated when surfaces are rubbed together. The understanding of tribocharging is of wide interest for several industrial applications and in particular the combination of tribocharging and triboemission may be important in lubricated contacts in the formation of boundary lubricant films. We report the use of a unique vacuum measurement system that enables to measure surface charge variations while simultaneously recording triboemission events during the sliding of a diamond tip on silica specimens. Results show for the first time that tribocharging and triboemission behavior are linked and depend on the surface wear. The contribution of contact-induced electrification to the charging of the surface is then described by means of density functional theory (DFT). Results give insight into the transfer of charge from the SiO 2 amorphous surface (silica) to the C(111) surface (diamond) and into the variation of charging during simulated sliding contact.

show abstract

“…Comparison of the lattice constants of different PTFE phases as predicted by the force field of Watkins and Jorgensen[32] with literature values ( a X-ray diffraction from Ref [41],. b DFT (PBE-D) results from Ref [42]…”

mentioning

confidence: 99%

A Combined Experimental and Atomistic Investigation of PTFE Double Transfer Film Formation and Lubrication in Rolling Point Contacts

et al. 2021

View full text Add to dashboard Cite

Solid lubricants such as polytetrafluoroethylene (PTFE) are used in rolling-element bearings (REBs) when conventional lubrication (i.e. by fluids or greases) cannot be applied owing to extreme operating conditions (e.g. high temperatures or vacuum). Often a double transfer film mechanism is used with a cage acting as a lubricant reservoir resupplying the REB with solid lubricant by cage wear. An increase in service life of such bearings requires a better understanding of the transfer processes in the sliding and rolling contacts. Here, we investigate the effect of PTFE resupply on friction and lubricant film formation in a steel/steel and steel/glass rolling contact by tribometry and classical molecular dynamics (MD). A ball-on-disk tribometer is enhanced by a pin-on-disk sliding contact that transfers PTFE to the disk. The experiment allows simultaneous in situ measurement of friction and film thickness by white light interferometry in the rolling point contact. Increasing the pin load results in an increased PTFE film thickness in the rolling contact accompanied by a significant decrease in friction. To elucidate the observed film transfer and friction mechanism, sliding MD simulations with a newly developed density-functional-based, non-reactive force field for PTFE-lubricated iron oxide surfaces are performed. A strong adhesion of PTFE chains to iron oxide drives transfer film formation, whilst shear-induced chain alignment within PTFE results in reduced friction. The simulations reveal an anti-correlation between PTFE film thickness and friction coefficient—in agreement with the experiments. These investigations are a first step towards methods to control PTFE transfer film formation in REBs. Graphic Abstract

show abstract

First-Principles Insights into the Structural and Electronic Properties of Polytetrafluoroethylene in Its High-Pressure Phase (Form III)

Cited by 11 publications

References 58 publications

Ab Initio Study of Polytetrafluoroethylene Defluorination for Tribocharging Applications

Ab Initio Study of Polytetrafluoroethylene Defluorination for Tribocharging Applications

A Combined Experimental and Theoretical Study on the Mechanisms Behind Tribocharging Phenomenon and the Influence of Triboemission

A Combined Experimental and Atomistic Investigation of PTFE Double Transfer Film Formation and Lubrication in Rolling Point Contacts

Contact Info

Product

Resources

About