Ultrathin perfluoropolyether-silane (PFPE-silane) films offer excellent functionality as antifingerprint coatings for display touchscreens due to their oleophobic, hydrophobic, and good adhesion properties. During smartphone use, PFPE-silane coatings undergo many abrasion cycles which limit the coating lifetime, so a better understanding of how to optimize the film structure for improved mechanical durability is desired. However, the hydrophobic and ultrathin (1-10 nm) nature of PFPE-silane films renders them very difficult to experimentally characterize. In this study, the cohesive fracture energy and elastic modulus, which are directly correlated with hardness and better wear resistance of 3.5 nm-thick PFPE-silane films were, respectively, measured by double cantilever beam testing and atomic force microscopy indentation. Both the cohesive fracture energy and modulus are shown to be highly dependent on the underlying film structure. Both values increase with optimal substrate conditions and a higher number of silane groups in the PFPE-silane precursor. The higher cohesive fracture energy and modulus values are suggested to be the result of the changes in the film chemistry and structure, leading to higher cross-linking density. Therefore, future work on optimizing PFPE-silane film wear resistance should focus on pathways to improve the cross-linking density. Subcritical fracture testing in humid environments reveals that humidity negatively affects the fracture properties of PFPE-silane films.
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http://dx.doi.org/10.1021/acs.langmuir.2c00625 | DOI Listing |
Langmuir
May 2022
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305-2205, United States.
Ultrathin perfluoropolyether-silane (PFPE-silane) films offer excellent functionality as antifingerprint coatings for display touchscreens due to their oleophobic, hydrophobic, and good adhesion properties. During smartphone use, PFPE-silane coatings undergo many abrasion cycles which limit the coating lifetime, so a better understanding of how to optimize the film structure for improved mechanical durability is desired. However, the hydrophobic and ultrathin (1-10 nm) nature of PFPE-silane films renders them very difficult to experimentally characterize.
View Article and Find Full Text PDFACS Appl Mater Interfaces
October 2018
Enhancing the mechanical durability of antifingerprint films is critical for its industrial application on touch-screen devices to withstand friction damage from repeated rubbing in daily usage. Using reactive molecular dynamics simulations, we herein implement adhesion, mechanical, and deposition tests to investigate two durability-determining factors: intrachain and interchain strength, which affect the structural stability of the antifingerprint film (perfluoropolyether) on silica. From the intrachain perspective, it is found that the Si-C bond in the polymer chain is the weakest, and therefore prone to dissociation and potentially forming a C-O bond.
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