Insights into the Mechanical Properties of Ultrathin Perfluoropolyether–Silane Coatings

Abstract

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.

Comparative Molecular Dynamics Simulation of Wetting on Liquid-like Surfaces

“…However, the nanometer-thick nature of surface-tethered brushes presents a significant challenge in achieving precise control over grafting in experimental practices. 30 Moreover, it is also difficult to directly observe the interactions between the grafted chains and droplets at molecular scales using experimental methods. Hence, there is a need to devise numerical methodologies for simulating the underlying principles governing LLS, enabling subsequent simulations under specific conditions.…”

“…Understanding how grafting parameters and the configuration of mobile chains affect the wetting characteristics of surfaces at the molecular level is crucial for optimizing the repellent performance. However, the nanometer-thick nature of surface-tethered brushes presents a significant challenge in achieving precise control over grafting in experimental practices . Moreover, it is also difficult to directly observe the interactions between the grafted chains and droplets at molecular scales using experimental methods.…”

Toward Water and Oil Repellent Coating: Synthesis of Fluorinated Methacrylate-Glycidyl Methacrylate Copolymers

“…This multifaceted approach addresses fouling challenges across diverse industrial settings, offering a versatile and effective solution. Among low-surface energy materials, fluorinated-based materials (e.g., perfluoro silanes, , perfluoro acids, , and perfluoro polymers − ) are particularly favored for their enhanced oil-repelling characteristics due to their lower surface energy compared to hydrocarbons (CH > CH 2 > CH 3 > CF 2 > CF 2 H > CF 3 ). − Hare et al conducted the synthesis of films by depositing perfluorododecanoic acid (PFDoA) onto metal surfaces. The surface energy of PFDoA films was determined to be 6 mN/m 2 , the lowest among known surface energies.…”

“…To date, various fluorinated polymers (fluorinated poly(methacrylates/acrylates), , fluorinated polyurethanes, , and perfluoro-polyethers ,, have been used as low-surface energy coatings. Moreover, for industrial applications, the stability of hydrophobic/oleophobic coatings is paramount.…”