title: Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy.
abstract: Atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. The comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Jennifer M
authors: JM
authors: Black
authors: State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China.
authors: Mengyang
authors: M
authors: Zhu
authors: Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Pengfei
authors: P
authors: Zhang
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Raymond R
authors: RR
authors: Unocic
authors: State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China.
authors: Daqiang
authors: D
authors: Guo
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: M Baris
authors: MB
authors: Okatan
authors: Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Sheng
authors: S
authors: Dai
authors: Department of Chemical &Biomolecular Engineering and Multiscale Modeling and Simulation Center, Vanderbilt University, Nashville, TN, 37235, USA.
authors: Peter T
authors: PT
authors: Cummings
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Sergei V
authors: SV
authors: Kalinin
authors: State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China.
authors: Guang
authors: G
authors: Feng
authors: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
authors: Nina
authors: N
authors: Balke