Research Article


2019, 12(1): 57–61


Detecting van der Waals forces between a single polymer repeating unit and a solid surface in high vacuum

Wanhao Cai§, Chen Xiao§, Linmao Qian, and Shuxun Cui (*)

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Key Laboratory of Advanced Technologies of Materials (Ministry of Education), Southwest Jiaotong University, Chengdu 610031, China
§ Wanhao Cai and Chen Xiao contributed equally to this work.

Keywords: van der Waals forces, high vacuum, atomic force microscopy, single-molecule studies, polymer desorption
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Ubiquitous van der Waals (vdW) forces are very important for nanostructures. Although the vdW forces between two surfaces (or two layers) have been measured for several decades, a direct detection at the single-molecule level is still difficult. Herein, we report a novel method to solve this problem in high vacuum by means of AFM-based single-molecule force spectroscopy (SMFS). Solvent molecules and surface adsorbed water are removed thoroughly under high vacuum so that the situation is greatly simplified. A constant force plateau can be observed when a polymer chain is peeled off from a substrate in high vacuum. Accordingly, the vdW forces between one polymer repeating unit and the substrates can be obtained. The experimental results show that the vdW forces (typical range: 21–54 pN) are dependent on the species of substrates and the size of polymer repeating unit, which is in good accordance with the theoretical results. It is expected that this novel method can be applied to detect other non-covalent interactions (such as hydrogen bond and π-π stacking) at the single-molecule level in the future.
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Detecting van der Waals forces between a single polymer repeating unit and a solid surface in high vacuum. Nano Res. 2019, 12(1): 57–61

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