The Effect of UV Irradiation on the Z-Tetraol Boundary Lubricant

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The UV irradiation of Z-Tetraol films on amorphous nitrogenated carbon surfaces was investigated. COF2 evolution, captured in the gas phase, decreased with increasing number of OH end groups in the order: Z > Zdol > Z-Tetraol after UV irradiation. Both UV irradiation and annealing on 11 Å Z-Tetraol films produced virtually identical interfacial properties - surface energy as a function of bonded fraction. The UV-irradiated 11 Å Z-Tetraol films also demonstrated equilibrium behavior exhibiting bonding or debonding to the asymptotic 80% bonded level under ambient conditions. UV-irradiated thick films of Z-Tetraol (∼ 20-40 Å) exhibited film properties that differed from the non-irradiated films. The oscillations in the polar component of the surface energy, normally observed in Z-Tetraol films and attributed to amphiphilic structuring, disappeared. Terraced flow exhibited a rapidly moving front below ∼ 10 Å compared to the remainder of the irradiated film. Both observations were tentatively attributed to loss of OH functionality. The latter was verified by chemical extraction and subsequent analyses by NMR and TGA.