Határfelületi (víz)molekulák orientációs statisztikája

1. Határfelületi (víz)molekulák orientációs statisztikája Horvai György, Jedlovszky Pál, Vincze Árpád, Pártay Lívia BME, ELTE, ZMNE

2. OVERVIEW OF PREVIOUS STUDIES • i.) No particular orientational preference • Carpenter, Hehre, JPC94 (1990) 531 hexane • ii.) Dipole of water molecules located • closest to the apolar phase points toward • the apolar phase • farther from the apolar phase points toward • the aqueous phase • van Buuren et al., JPC97 (1993) 9206 decane • iii.) Dipole of water molecules is parallel with • the interface • Linse, JCP86 (1987) 417, benzene • Benjamin, JCP97 (1992) 1432 1,2-dichloroethane • iv.) Dipole of water molecules is almost parallel with the • interface, however, it deviates from parallel alignment • toward the apolar rather than the aqueous • phase for waters located closest to • the apolar phase • toward the aqueous rather than the apolar • phase for waters located farther from the • apolar phase • Zhang et al., JCP103 (1995) 10252, octane • Fernandes et al., JPC/B103 (1999) 6290 2-heptanone

3. H H O O H H H O H H O H H O H H O H H O H • v.) The H-H vector of the water molecules located • closest to the interface is perpendicular • to the interface • Benjamin, JCP97 (1992) 1432 1,2-dichloroethane • Chang and Dang, JCP104 (1996) 6772 CCl4 • Vincze et al., Anal. Sci.17 (2001) i317 1,2-dichloroethane • vi.) The H-H vector of the water molecules located farther • from the interface has no particular orientational • preference • Benjamin, JCP97 (1992) 1432 1,2-dichloroethane • vii.) The H-H vector of the water molecules located farther from • the interface is parallel with the interface • Chang and Dang, JCP104 (1996) 6772 CCl4

4. Orientation of water at the air/water interface

5. Concept of the bivariate joint distributions The interfacial orientation of the molecules can be analyzed at different levels of statistics: 1.Level of the orientational profiles of various orientational parameters Average of parameters describing the orientation of various, molecule-fixed vectors relative to the interface – irrespective the other vectors Profiles along the interface normal 2.Level of monovariate distributions of the individual orientational parameters Distribution of these parameters in separate water layers along the interface normal 3.Level of bivariate distribution of two independent orientational parameters Joint distribution of two independentorientational parameters in separate water layers along the interface normal. (One to one mapping of orientation on the parameters not sufficient. Distribution in bulk should be uniform!)

6. Orientációs eloszlási térképek a felszínközeli rétegekben X II I

7. X I II

8. Dependence of the results on the apolar phase

9. Dependence of the results on the aqueous phase Liquid/vapor interface of water-methanol mixtures WATER ORIENTATION MAPS

10. DENSITY PROFILES DENSITY PROFILES

11. Non-equilibrium dynamics and structure of interfacial ice Oliviero Andreussi, Davide Donadio, Michele Parrinello, Ahmed H. Zewail Chemical Physics Letters 2006 Figure 4 Orientational probability distribution P(cosθ,φ) for the three regions of threebilayer thick interfacial ice. The two independent orientational parameters (θ,φ) are theangular polar coordinates of the vector normal to the substrate's surface, in a coordinateframe fixed to the individual water molecules [34]. The presence of four preferredorientations is evident for the crystalline systems (below 180 K). At higher temperaturessystems present orientational disorder in the bulk region, while molecules at the freesurface tend to point towards the inner layers and a more structured bilayer is present atthe ice-substrate interface