Ordered water structure at hydrophobic graphite interfaces observed by 4D, ultrafast electron crystallography
Interfacial water has unique properties in various functions. Here, using 4-dimensional (4D), ultrafast electron crystallography with atomic-scale spatial and temporal resolution, we report study of structure and dynamics of interfacial water assembly on a hydrophobic surface. Structurally, vertically stacked bilayers on highly oriented pyrolytic graphite surface were determined to be ordered, contrary to the expectation that the strong hydrogen bonding of water on hydrophobic surfaces would dominate with suppressed interfacial order. Because of its terrace morphology, graphite plays the role of a template. The dynamics is also surprising. After the excitation of graphite by an ultrafast infrared pulse, the interfacial ice structure undergoes nonequilibrium "phase transformation" identified in the hydrogen-bond network through the observation of structural isosbestic point. We provide the time scales involved, the nature of ice-graphite structural dynamics, and relevance to properties related to confined water.
Additional Information© 2009 by the National Academy of Sciences. Contributed by Ahmed H. Zewail, December 5, 2008 (sent for review November 13, 2008). We thank Dr. Nuk Gedik for his participation in the initial phase of this work; the collaborative effort (21) for study of other substrates and materials will be the subjects of other reports. We also thank Professors H. Eugene Stanley, Sven Hovmöller, and Dongping Zhong for critical reading and helpful suggestions. This work was supported by the National Science Foundation and the Air Force Office of Scientific Research in the Gordon and Betty Moore center for physical biology at Caltech. Author contributions: D.-S.Y. and A.H.Z. performed research and wrote the paper. The authors declare no conflict of interest.
Published - Yang2009p1218P_Natl_Acad_Sci_Usa.pdf