Direct comparison between chemisorption and physisorption: a study of poly(ethylene glycol) by means of single-molecule force spectroscopy

Abstract

Sample preparation is crucial to the studies of polymers on surfaces and interfaces. For studies using single-molecule force spectroscopy (SMFS), sample preparation is the key to obtain high-quality data. In each of the previous SMFS studies, either physisorption or chemisorption was applied in the sample preparation. However, a direct comparison on the same polymer species with both of the two strategies has not been reported yet. With two methods (physisorption, “PS”, or chemisorption, “CS”) and two surfaces (AFM tip or quartz substrate), four types of samples of poly(ethylene glycol) (PEG) can be prepared from the polymer solution. The performance of these samples with the same species of PEG are directly compared by SMFS. It is found that among these samples, two of them, i.e., tip-CS and substrate-PS, are suitable for SMFS. The advantage of substrate-PS is the simple preparation. In contrast, the advantage of tip-CS is the higher rupture force and the lower sample consumption. The former feature will be time saving if a high rupture force is needed in the analysis. The latter feature will be economic when an expensive sample is used. The other two types of samples, i.e., tip-PS and substrate-CS show lower data yield and lower rupture force. In summary, the tip-CS and substrate-PS are recommended for sample preparation in SMFS. The tip-CS is the most promising protocol, if a functionalized polymer sample is available.