title: Interfacial gas nanobubbles or oil nanodroplets?
abstract: The existence of nanobubbles at a solid-liquid interface with high stability has been confirmed by myriad experimental studies, and their gaseous nature has also been extensively verified. However, nanodroplets of polydimethylsiloxane (PDMS) recently observed in the atomic force microscopy (AFM) measurement of nanobubbles plague the nanobubble community. It may easily lead to wrong interpretations of the AFM results and thus hinders further application of the already widely used AFM in nanobubble studies. Therefore, finding a direct experimental solution to distinguish nanobubbles from nanodroplets in AFM measurements is a matter of great urgency. Herein, we first developed an effective and reproducible method to produce PDMS nanodroplets at the highly ordered pyrolytic graphite (HOPG)/water interface. From their size, contact angle, and stiffness, the formed PDMS nanodroplets are not distinguishable from nanobubbles. However, the force curves on these two objects are strikingly different from each other, i.e., a peculiar plateau in both the approach and retraction curves was found on nanobubbles whereas they changed linearly between the jump-in and jump-off point on PDMS nanodroplets. Thus, the present study not only provided a simple and effective procedure to generate PDMS nanodroplets but also paved a simple practical and in situ way to discriminate nanobubbles from the PDMS nanodroplets by direct AFM force measurements.
authors.affiliation: Shanghai Synchrotron Radiation Facility, Chinese Academy of Sciences, Shanghai 201204, China. gaoxingyu@sinap.ac.cn zhanglijuan@sinap.ac.cn and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Xingya
authors.identifier: http://orcid.org/0000-0001-5242-6458
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Traction Power, School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu 610031, China. byzhao@swjtu.edu.cn.
authors.forename: Binyu
authors.initials: B
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Hu
authors.affiliation: Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Shuo
authors.initials: S
authors.lastname: Wang
authors.affiliation: Shanghai Synchrotron Radiation Facility, Chinese Academy of Sciences, Shanghai 201204, China. gaoxingyu@sinap.ac.cn zhanglijuan@sinap.ac.cn and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Renzhong
authors.initials: R
authors.lastname: Tai
authors.affiliation: Shanghai Synchrotron Radiation Facility, Chinese Academy of Sciences, Shanghai 201204, China. gaoxingyu@sinap.ac.cn zhanglijuan@sinap.ac.cn.
authors.forename: Xingyu
authors.initials: X
authors.lastname: Gao
authors.affiliation: Shanghai Synchrotron Radiation Facility, Chinese Academy of Sciences, Shanghai 201204, China. gaoxingyu@sinap.ac.cn zhanglijuan@sinap.ac.cn and Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Zhang