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Molecular friction dissipation and mode coupling in organic monolayers and polymer films
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Image of FIG. 1.
FIG. 1.

(a) Energy diagram for Eyring model. (b) Conceptual drawing illustrating the activation volumes associated with pressure and shear.

Image of FIG. 2.
FIG. 2.

General procedure for obtaining the Eyring model parameters , , , and . Dotted lines indicate a path of high uncertainty for . In this study is obtained from IFA.

Image of FIG. 3.
FIG. 3.

IFA data analysis, horizontal shifting provides activation energy information, while vertical shifting provides cooperativity (entropic) information.

Image of FIG. 4.
FIG. 4.

(a) Representative friction-velocity master curve of ODPA for a ∼400 nm radius tip as imaged () by transmission electron microscopy. (b) The slope of the corresponding Arrhenius plot of the shift factor ln vs , reveals an activation energy of 46 kJ/mol independent of load. : Chemical structure of ODPA. (c) , and plots as a function of temperature for a 400 nm tip radius lever, and a constant pressure of 34 MPa Values are averaged over all velocities, and the error bars represent the standard deviation. The data is contrasted to from IFA (represented by the dashed line).

Image of FIG. 5.
FIG. 5.

Shear stress data as a function of temperature for various velocities measured at = 23 MPa using the large tip (∼400 nm). Line slopes are –, and are −0.0086, −0.0135, −0.0177, −0.0246, −0.0320, and −0.0368 MPa/K for 0.5, 1, 2, 5, 10, and 50 μm/s, respectively. (Inset) values as a function of log scan velocity calculated from values and (15) , showing that ln = 9.97ln+143.

Image of FIG. 6.
FIG. 6.

Plot of ln vs 1/ for various ln ( ) values from ODPA and PtBA master curves. Each data point for ODPA is averaged over six loads. The inset highlights the ln-intercept data extrapolation with the dotted lines representing high and low deviations from the selected (solid line) value. The corresponding median values are provided for ODPA and PtBA.

Image of FIG. 7.
FIG. 7.

(a) Master curve for PtBA (see ) at a reference temperature of 315 K. (b) Half logarithmic representation of the shift factor as a function of inverse temperature and the corresponding WLF fit along with the literature WLF expression for peak values from dielectric spectroscopy measurements (Ref. 33 ). (c) Vertical shift values as a function of temperature, reveal the onset of vertical shifting near .

Image of FIG. 8.
FIG. 8.

Entropic, Δ enthalpic Δ and apparent energy contributions as function of temperature for PtBA .

Image of FIG. 9.
FIG. 9.

Plot of , , values as a function of temperature for a constant pressure of 99 MPa, error bars represent the standard deviation. The dashed line represents from IFA.

Image of FIG. 10.
FIG. 10.

(a) For slider-system coupling, the shear stress reveals a peak value, which leads to (b) negative and zero values of , and, consequently, (c) unphysical behavior for the Eyring parameters and Ω in the unextended Eyring model.

Image of FIG. 11.
FIG. 11.

IFA master curve for = 315 K, which corresponds to obtained above. Also included are Erying model fits at = 315 K, where = 1.5 × 10−27 m3, = 35–43 kJ/mol, = 1.92 × 10−28 m3, all of which were obtained by the same procedure as for ODPA mentioned above. was estimated to be 2.92 × 10−16 m2 assuming JKR contact mechanics (Ref. 26 ). For 315 K, = 1.0 occurs at a scan rate of 0.1 nm/s.


Generic image for table
Table I.

Erying model results for monolayers.

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Table II.

Compounded data of IFA and Eyring analysis for ODPA and PtBA.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Molecular friction dissipation and mode coupling in organic monolayers and polymer films