|AVS 55th International Symposium & Exhibition|
|Nanometer-scale Science and Technology||Tuesday Sessions|
|Presenter:||Z. Wang, Tsinghua University, China|
|Authors:||Z. Wang, Tsinghua University, China
Y. Zhang, Tsinghua University, China
X. Zhang, Tsinghua University, China
|Correspondent:||Click to Email|
In this presentation, we have demonstrated the first direct measurement of the interaction between pyrene and a graphite surface at the single molecular level in aqueous media by AFM-based single molecule force spectroscopy (SMFS). As a model system driven by π- π interactions, pyrene derivatives can effectively absorb onto the surface of carbon nanotubes and graphite particles. For the investigation of the interaction between pyrene and graphite, we have connected a pyrene molecule onto an AFM tip via a poly(ethylene glycol) (PEG) chain. The use of PEG as a flexible spacer provides a means for differentiating the force signals based on the extension length and thereby for avoiding the disturbance of the nonspecific interaction between the AFM tip and substrate. To confirm the single molecular rupture events of pyrene desorbed from graphite, we have employed modified-freely jointed chain model to fit the force curves, and the fitting parameters are in accordance with that of a single PEG chain. Meanwhile, we have analyzed the distribution of the extension of the force peaks, and found that the most probable value is consistent with the PEG coutour length. The statistics of the height of the force peaks shows that the strength of interaction between pyrene and graphite is ~55 pN at the loading rate of 4.0 nN/s. To investigate the dynamic behavior of the interaction between pyrene and graphite, we have performed the SMFS experiment with different retraction velocities to obtain the dynamic force spectroscopy. This result indicates that there is no loading rate dependence at the experiment conditions, and implies that our experiments were carried out under a quasi-equilibrium condition. Therefore, the observed rupture force should equal the adhesion force between pyrene and graphite. This research may open a new route to directly study π- π interactions at a single molecular level, leading to understanding of the formation of supramolecular assemblies through π- π interactions.