PFPE molecule

Mate and Novotny [42] studied the conformation of 0.5-13 nm thick Z-15 on a clean Si (100) surface by means of AFM and XPS. They found that the height for PFPE molecules to extend above a solid surface was no more than 1.5-2.5 nm, which was considerably less than the diameter of gyration of the lubricant molecules ranging between 3.2-7.3 nm. The measured height corresponds to a few molecular diameters of linear polymer chains whose cross-sectional diameter is estimated as 0.6-0.7 nm. The experimental results imply that molecules on a solid surface have an extended, flat conformation. Furthermore, they brought forward a model, as shown in Fig. 28, which illustrates two... 

As a crucial factor that dominates the behavior of lubricant flow, the mobility of PFPE molecules has been studied extensively in both experiments and simulations, through observing the spreading of the lubricant on solid substrates. Investigators, including Novotny [46], O Connor et al. [47], Min et al. [48], and Ma et al. [49], in collaboration with IBM scientists, carried out systemic experimental studies on spreading... 

Fig. 29—Sketch for the structure of functional PFPE molecules [45], where Rg is the radius of gyration of PFPE molecules and a is the diameter of PFPE molecules.

Figure 17 A sketch of the rigid units of an oligomeric PFPE molecule (a) the flexible bonds with freely jointed beads and springs for coarse-grained bead-spring model and (b) SRS model with polarity (red arrow).

Further employment of the coarse-graining process to represent PFPE molecules with few parameter models (having the least... 

Here, Np is the total number of beads in each PFPE molecule, (xg, yg, zg) are the coordinates of the PFPE molecular center of mass, and (x yir z() denote the bead coordinates. The perpendicular size of PFPE... 

Figure 30 A schematic of the parallel and perpendicular radius of gyration of PFPE molecule on the surface.

Shape effect of PFPE molecules or magnetic particles in suspension, including agglomeration phenomena at low concentration, interaction among these particles, and effects of floes can be examined via solution viscosity (r ) measurement. For a very dilute polymer solution [108], there is no interaction among polymer molecules, and the solution viscosity results from the contribution of the solvent plus the contribution of the individual polymer molecules. The intrinsic viscosity, therefore, is a measure of the hydrodynamic volume of a polymer molecule as well as the particle aspect ratio. Figure 1.24 shows the determination of the intrinsic viscosity for Zdol4000 in three different solvents. 

Figure 1.22. (a) Simple representation of PFPE molecules to illustrate temporal tube -like... 

Figure 1.26. (a) Simplest representation of PFPE molecule illustrating solvent effect (b) well-dispersed case (p = 1) and (c) poorly dispersed situation (p / 1). Dip coating after solvent evaporation to make film (d) well-dispersed solution and (e) poorly dispersed solution (resulting in flying noise and corrosion). 

To represent the molecular structure with reasonable accuracy as well as to reduce computational time, the coarse-grained, bead-spring model [Fig. 1.28(b)] was employed to approximate a PFPE molecule. This simplifies the detailed atomistic information while preserving the essence of the molecular internal structure [167]. The off-lattice MC technique with the bead-spring model was used to examine nanoscale PFPE lubricant film structures and stability with internal degrees of freedom [168],... 

In our model, a PFPE molecule is composed of a finite number of beads with different physical or chemical properties [Fig. 1.41]. For simplicity, we assume that all the beads, including the endbeads, have the same radius. Lennard-Jones... 

Figure 1.53. The bead-spring model may be used to simulate PFPE molecules in head-disk interface (HDI), which couple with slider dynamics via steep pressure and temperature gradients, which appears in HAMR technology [35],...

In this model, a PFPE molecule is composed of a finite number of beads with different physical or chemical properties. For simplicity, we assume that all the beads, including the end-beads, have the same radius. Lennard-Jones and van der Waals potentials were used for nonpolar bead-bead and bead-wall interactions, respectively. For polar interactions, exponential potential functions were added to both end-bead end-bead and end-bead wall interactions. For the bonding potential between adjacent beads in the chain, a finitely extensible nonlinear elastic model was used. For example, PFPE Zdol can be characterized differently from PFPE Z by assigning the end-bead a polarity originating from the hydroxyl group in the chain end. 

The purpose of XPS characterization was to identify whether or not the target film had been properly deposited, its chanical state and chanical interactions between SAM molecules and PFPE molecules, etc. For example, the amount of PFPE bonded can be obtained in the case of PFPE-overcoated SAMs with and without thermal treatment. Figure 6.3a shows the wide-scan spectra of the SAMs-modified and unmodified Si surfaces, and fig. 6.3b compares the wide-scan spectra of PFPE (as lubricated) onto SAM surfaces and Si. The wide-scan spectra of the three different SAMs qualitatively confirm the successful formation of respective SAMs on Si. For example, APTMS-modified Si shows a strong Nls peak, which must have resulted from the amine groups of APTMS molecules. The presence of the FIs peak on all PFPE-coated surfaces supports the presence of PFPE. 

PFPE coating onto SAM surfaces reduces the coefficient of friction (table 6.1) irrespective of the initial coefficient of friction of SAM surfaces. The reason for this behavior is that the top PFPE layer influences the initial coefficient of friction in all cases, regardless of the substrate. PFPE molecules offer a lower resistance to the shearing action and hence show a lower coefficient of friction. 

FIGURE 6.6 Molecular model of PFPE on (a) OTS SAM and (b) APTMS/GPTMS (refer to text for details). Thicker lines in (b) are used for strongly adsorbed, and the thinner lines for mobile PFPE molecules. (Reprinted from Satyanarayana, N., and Sinha, S. K. 2005. J. Phys. D Appl. Phys. 38 (18) 3512-22. With permission from Institnte of Physics Pnblishing.)... 

PFPE overcoating onto all SAM surfaces increases the wear durability, and the extent of improvement in wear durability depends on the SAM surface properties such as surface wettability, chemical interactions between SAM molecules and PFPE molecules, and molecular packing density and order in the SAM surfaces. The extent of improvement of wear durability is very high when PFPE is coated onto reactive SAM surfaces (such as APTMS and GPTMS SAMs) and is very low when PFPE is coated onto nonpolar OTS SAM. This is mainly due to the differences in the extent of chemical interactions between PFPE and SAM molecules. 

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