title: Modeling the Interaction between AFM Tips and Pinned Surface Nanobubbles.
abstract: Although the morphology of surface nanobubbles has been studied widely with different AFM modes, AFM images may not reflect the real shapes of the nanobubbles due to AFM tip-nanobubble interactions. In addition, the interplay between surface nanobubble deformation and induced capillary force has not been well understood in this context. In our work we used constraint lattice density functional theory to investigate the interaction between AFM tips and pinned surface nanobubbles systematically, especially concentrating on the effects of tip hydrophilicity and shape. For a hydrophilic tip contacting a nanobubble, its hydrophilic nature facilitates its departure from the bubble surface, displaying a weak and intermediate-range attraction. However, when the tip squeezes the nanobubble during the approach process, the nanobubble shows an elastic effect that prevents the tip from penetrating the bubble, leading to a strong nanobubble deformation and repulsive interactions. On the contrary, a hydrophobic tip can easily pierce the vapor-liquid interface of the nanobubble during the approach process, leading to the disappearance of the repulsive force. In the retraction process, however, the adhesion between the tip and the nanobubble leads to a much stronger lengthening effect on nanobubble deformation and a strong long-range attractive force. The trends of force evolution from our simulations agree qualitatively well with recent experimental AFM observations. This favorable agreement demonstrates that our model catches the main intergradient of tip-nanobubble interactions for pinned surface nanobubbles and may therefore provide important insight into how to design minimally invasive AFM experiments.
authors.affiliation: State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology , Beijing 100029, China.
authors.forename: Zhenjiang
authors.initials: Z
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology , Beijing 100029, China.
authors.forename: Yawei
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology , Beijing 100029, China.
authors.forename: Qianxiang
authors.initials: Q
authors.lastname: Xiao
authors.affiliation: Physical Chemistry I, Department of Chemistry and Biology & Research Center of Micro and Nanochemistry and Engineering (Cμ), University of Siegen , Adolf-Reichwein-Str. 2, 57076 Siegen, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schönherr
authors.affiliation: State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology , Beijing 100029, China.
authors.forename: Xianren
authors.initials: X
authors.lastname: Zhang