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Wei C, Zhao W, Shi X, Pei C, Wei P, Zhang J, Li H. Thick Two-Dimensional Water Film Confined between the Atomically Thin Mica Nanosheet and Hydrophilic Substrate. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:5130-5139. [PMID: 30907594 DOI: 10.1021/acs.langmuir.8b04232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The interesting properties of water molecules confined in a two-dimensional (2D) environment have aroused great attention. However, the study of 2D-confined water at the hydrophilic-hydrophilic interface is largely unexplored due to the lack of appropriate system. In this work, the behavior of water molecules confined between an atomically thin mica nanosheet and a hydrophilic SiO2/Si substrate was investigated using an atomic force microscope in detail at ambient conditions. The confined water molecules aggregated as droplets when the relative humidity (RH) of the environment was 11%. A large-area 2D water film with a uniform thickness of ∼2 nm was observed when the mica flake was incubated at 33% RH for 1 h before being mechanically exfoliated on a SiO2/Si substrate. Interestingly, the water film showed ordered edges with a predominant angle of 120°, which was the same with the lattice orientation of the mica nanosheet on top of it. The water film showed a fluidic behavior at the early stage and reached a stable state after 48 h under ambient conditions. The surface properties of the upper mica nanosheet and the underlying substrate played a crucial role in manipulating the behavior of confined water molecules. When the surface of the upper mica nanosheet was modified by Na+, Ni2+, and aminopropyltriethoxysilane (APS), only some small water droplets were observed instead of a water film. The surface of the underlying SiO2/Si substrate was functionalized by hydrophilic APS and hydrophobic octadecyltrimethoxysiliane (OTS). The small water droplets were imaged on a hydrophobic OTS-SiO2/Si substrate, while the water film with regular edges was maintained on a hydrophilic APS-SiO2/Si substrate. Our results might provide an alternative molecular view for investigating structures and properties of confined water molecules in 2D environments.
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Affiliation(s)
- Cong Wei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Weihao Zhao
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Xiaotong Shi
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Chengjie Pei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Pei Wei
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Jindong Zhang
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
| | - Hai Li
- Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM) , Nanjing Tech University (NanjingTech) , 30 South Puzhu Road , Nanjing 211816 , P.R. China
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