title: Hidden Nanobubbles in Undersaturated Liquids.
abstract: Here, we propose theoretically the existence of a new type of nanobubble in undersaturated liquids. These nanobubbles have a concave vapor-liquid interface featured with a negative curvature rather than a positive curvature for nanobubbles in supersaturated liquids, so that they often hide inside of the substrate textures and it might not be easy to characterize them through atomic force microscopy (AFM) measurements. However, these hidden nanobubbles are still stabilized by the contact line pinning effect and stay at the thermodynamically metastable state. We further demonstrate that similar to the nanobubbles in supersaturated liquids the contact angle of the hidden nanobubbles is more sensitive to the nanobubble size rather than the substrate chemistry, and their curvature radius is dependent on the chemical potential but independent of the base radius. Finally, we show several potential situations for the appearance of the hidden nanobubbles.
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: State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology , Beijing 100029, China.
authors.forename: Xianren
authors.initials: X
authors.lastname: Zhang