Speaker : Dr. Wanhao Cai Affiliation : University of Freiburg, Germany Region : Europe Year : 2022 Language : English Friction has been a major burden to the material systems across different length scales. To realize a high adhesive strength with low friction, a high directional anisotropy of the interfacial interaction is strongly required. π-π-stacking is an important interaction whose anisotropy has been observed at the large scale such as for graphene interfaces.1 However, due to limited characterization capabilities, a comprehensive understanding of π-π-stacking has remained poorly understood. Here we use atomic force microscopy-based stereographic single molecule force spectroscopy2 to study the direction-dependent strength of π-π stacking, namely a single pyrene molecule on highly oriented pyrolytic graphite. We find the friction force along shear direction is at least three orders of magnitudes lower than the adhesive force along out-of-plane direction, indicating a superlubricity at the single-molecule level. This unique anisotropy is in contrast to other molecular interactions, such as the high friction for the thiol-Au coordination bond. Our results provide a bottom-up understanding of the interfacial behavior based on molecular interactions, which is helpful for the rational design of materials. References 1. Hod, O.; Meyer, E.; Zheng, Q.; Urbakh, M., Structural superlubricity and ultralow friction across the length scales. Nature 2018, 563, 485-492. 2. Cai, W.; Bullerjahn, J. T.; Lallemang, M.; Kroy, K.; Balzer, B. N.; Hugel, T., Angle-dependent strength of a single chemical bond by stereographic force spectroscopy. Chem. Sci. 2022, 13, 5734-5740.
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