The structure of the surface of pure liquids

Abstract

This paper reviews the progress in the study of the structure of the surface of pure liquids made in the last 10-20 years. This area of research has benefited enormously in recent years from developments in experimental techniques (especially x-ray scattering methods based on third-generation synchrotron sources, and advanced optical techniques) and theory (particularly computer simulation and density functional theory). The review is predominantly experimentally based, and focuses very much on some recent exciting new results and developments. Specific systems or phenomena that are discussed are molecular ordering and orientation at the surface, atomic-scale layering at liquid metal surfaces, surface freezing in liquid alkanes and alcohols, surface melting and pre-melting at the water surface, thermal roughness (capillary waves) in simple liquids, and visco-elastic surface waves. Both the liquidvapour and liquid-solid interfaces are considered. Some details of the principal experimental techniques exploited, x-ray reflectivity, diffuse x-ray scattering, grazing incidence x-ray diffraction, ellipsometry, light scattering, will be given, The experimental developments have gone very much in conjunction with substantial theoretical advances, and the principal theoretical concepts will be briefly discussed.

Size dependence of nanostructures: Impact of bond order deficiency

“…In many cases, surface melting and evaporation often occur at temperatures lower than the corresponding bulk values [260,261]. For substrate-supported nanosolids with relatively free surfaces, the T m decreases with particle size (termed as undercooling).…”

Fluid interfacial nanoroughness measurement through the morphological characteristics of graphene

“…A variety of liquid surfaces, including argon, carbon tetrachloride, water, helium, alkanes, and alcohols, have been studied extensively (refer to Penfold's review). 4 Recently, Yang et al used an atomic force microscope (AFM) to investigate the roughness of a liquid interface and successfully measured nanoroughness and its temperature dependency. This study implies that AFM can be used to measure the roughness of a highly flexible surface.…”

“…6 However, this approach has limitations when complex surface phenomena are considered, such as atomic-scale layering, molecular orientation preference, and surface freezing and melting, that can significantly affect the nanoroughness of the liquid surface. 4 Molecular dynamics (MD) simulation can provide an alternative solution to overcome these problems. Several studies have already proved the reliability of numerical methods for describing interfaces, including a liquid-vapor interface, [8][9][10][11] liquid-liquid interface, [12][13][14] and liquidsurfactant-liquid interfaces.…”

Angle resolved ion scattering spectroscopy reveals the local topography around atoms in a liquid surface

“…5,6 In favourable cases the electron density profile can be interpreted in terms of the profile of chemical species. 7 With non-linear optical methods the orientation of molecules is determined.…”