The Photodissociation of Perfluoropolyethers by Ultraviolet Light

Abstract

Abstact The 172 nm ultraviolet (UV) photodissociation of perfluoropolyether (PFPE) boundary lubricants is examined experimentally and theoretically. Carbonyl fluoride, COF 2 , is the major gas phase product that results from the UV irradiation of non-functionalized perfluoropolyethers containing the perfluoromethylene oxide, perfluoroethylene oxide, and the perfluoro-n-propylene oxide monomer units. The energetics for COF 2 evolution from the carbon centered radicals R-OCF 2 OCF 2 Á , R-CF 2 CF 2 OCF 2 Á ; and from the oxygen centered radicals R-CF 2 OCF 2 O Á , R-CF 2 CF 2 O Á are quantified via ab initio calculations. The electronic structure of the transition state geometries leading to COF 2 dissociation is characterized. COF 2 originating from oxygen-centered radicals, leaving behind a carbon-centered radical on the PFPE main chain, appears to be the most energetically favorable dissociation pathway.

Effect of Ultraviolet Irradiation on Adhesion of Nanometer-Thick Lubricant Films Coated on Magnetic Disk Surfaces

“…Supposing bonded films as uniformly distributed solid-like continuum films of thickness , solid-solid adhesive force acting on the spherical probe of radius is given by [13], [15] (6) where ) is the separation distance between the probe and sample surfaces at intimate contact [13], is the interaction energy per unit area between the probe and sample surfaces in a planar geometry with separation , and , are the Hamaker constants for the lubricant/air/probe/air and substrate/lubricant/probe/air interfaces, respectively. With the following equation [15] and a refractive index of 1.52 for the probe (7) and…”

Fabricating Nanometer-Thick Simultaneously Oleophobic/Hydrophilic Polymer Coatings via a Photochemical Approach

“…25,26 However, recently Guo and Waltman challenged this mechanism based on the argument that the amount of photoelectrons from the substrate generated by UV is not enough to account for the bonding between the substrate and PFPEs. 27,28 Guo and Waltman proposed that UV irradiation induces the photodissociation of PFPE polymer itself and thus initiates the bonding between PFPE and the solid substrate, which is supported by the facts that the molecular weight of PFPE decreases after UV irradiation. 27 More recently, as shown in Scheme 1, Nakakawaji 37 proposed that both the excitation of the substrate and the excitation of the PFPE contribute to the bonding between PFPE and the substrate under UV irradiation.…”

Strong fragmentation processes driven by low energy electron attachment to various small perfluoroether molecules

“…Radical propagation and termination then cross-link the polymer resulting in a strong bonding to the surface. However, this proposed mechanism was questioned in [13] , where UV induced photodissociation processes were favoured for example due to the observation of bonding even for 254 nm UV light in contrast to previous studies (see detailed discussion in [14] ). Moreover, it should be noted that chemical bonding was also observed by irradiation even with visible laser light at 532 nm [15] , i.e., using the same argumentation like for the 254 nm UV experiments, another mechanisms other than DEA are also operative to induce chemical bonding.…”