Spreading of perfluoropolyalkylether films on amorphous carbon surfaces

Abstract

Spreading of perfluoropolyalkylether thin films on amorphous carbon surfaces has been studied by scanning microellipsometry. Two types of perfluoropolyalkylethers with the same main-chain structure and various molecular weights (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end groups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn0.6, where Mn is the mean molecular weight, with the second layer being nearly twice as thick as the first layer. This layered structure was not observed for Z in the molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular weight. Possible molecular conformations near the solid surface are discussed. The spreading of binary blends of Zdol–Zdol, Z–Z, and Zdol–Z were also studied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight behaved like that of a lubricant with an intermediate molecular weight. The diffusion coefficient of a blend was found to obey the additivity of viscosity. For Zdol–Z blends, however, the faster moving Z molecules migrate through the network of the slower moving Zdol molecules, and form a monolayer ahead of Zdol.

The dynamic behavior of ultrathin lubricant films

“…The film diffusion coefficients for different x 2 lie between those of two pure components. Similar results were observed experimentally by Ma et al (1999). The translational motion of the tagged molecule is modified strongly by the background oligomer matrix and produces deviation from the ideal mixture, whereby most likely, the conjecture of core-shell structure greatly restricts the high mobility of the short chains locating inside the shell, which makes the longchain molecules dominant in determining the mixed film diffusion.…”

“…As h fi r, the molecules, most likely, lie flat on the solid surface to form a solid-like monolayer. It is reported that the dependence of the maximum diffusion coefficient on MW is a = 0.9 for Zdol while a = 0.8 for Z (Ma et al 1999). Thus, our simulation results qualitatively agree with those reported.…”

“…As a result, the investigation of the spontaneous spreading of ultrathin lubricant films has attracted considerable interest. The spreading experiments were carried out (O'Connor et al 1996;Ma et al 1999) using scanning microellipsometry (SME) in a controlled temperature and humidity environment to monitor the PFPE film thickness profiles on silica and carbon surfaces, respectively. Monte Carlo (MC) simulation, based on a simple reactive sphere model (Vinay et al 2000), was produced to interpret the spreading or replenishment characteristics of the SME profiles.…”

Fiber Wobbling Method for Dynamic Viscoelastic Measurement of Liquid Lubricant Confined in Molecularly Narrow Gaps

“…They all have the random coil structures in their bulk sate. Their chemical formulas, molecular weights, length of the main chains, and gyration diameters are summarized in Table 1 [12]. The end groups of Zdol2000 and 4000 are different from that of Z03.…”

Evaluation of ultraviolet assisted bonding between lubricant and diamond-like carbon through spreading of molecularly thin perfluoropolyether lubricant

“…The lubricant was fractionated to give a molecular weight of 4,000 g/mol. The lubricant's radius of gyration is estimated to be about 1.4 nm from the data of PFPE Fomblin Z and Z-DOL based on the relation that the radius is proportional to the square root of the molecular weight (Ma et al 1999a). A special feature of this lubricant is its high photosensitivity, which enables efficient bonding between the lubricant and DLC.…”