Surface structure, quantitative methods

Traube s rule accommodates the balance between hydrophobicity and hydro-philicity. It has been extended somewhat and formalized with the development of quantitative methods to estimate the surface area of molecules based on their structures [19, 237]. The molecular surface area approach suggests that the number of water molecules that can be packed around the solute molecule plays an important role in the theoretical calculation of the thermodynamic properties of the solution. Hence, the molecular surface area of the solute is an important parameter in the theory. In compounds other than simple normal alkanes, the functional groups will tend to be more or less polar and thus relatively compatible with the polar water matrix [227,240]. Hence, the total surface area of the molecule can be subdivided into functional group surface area and hydro carbonaceous surface area . These quantities maybe determined for simple compounds as an additive function of constituent groups with subtractions made for the areas where intramolecular contact is made and thus no external surface is presented. 

Almost all of the existing quantitative data on surface structure was obtained through experimental techniques that involve the propagation and scattering of electrons in solids. This class of surface probes includes the whole range of fine-structure techniques, in addition to LEED and angle-resolved photoemission experiments. This chapter will provide a theoretical description of these techniques and the methods of analyzing the experimental data to determine surface structure. 

The development by Muller (393) of the field ion microscope gave a considerable thrust to studying surface structures. In a recent modification of this technique, Panitz (394) designed a field desorption spectrometer that promises determination of the crystallographic distribution of species on metal surfaces. Secondary ion mass spectroscopy can also provide some quantitative information of surface species by sputtering atoms with an inert gas ion beam and detecting them by mass spectrometry. Submonolayers of adsorbed gases can be studied by this method (395). 

Surface roughness measurement can be characterized using either quantitative or qualitative methods. Qualitative techniques include optical appearance such as the reflectivity of a surface or the strength of the machining lay as well as dragging a thumbnail across the surface as a crude tactile sensor. Quantitative analysis has evolved from simple two-dimensional profilometry to more advanced three-dimensional area analysis where information regarding surface structure can be easily obtained. 

During such surface treatments the surface topography is often transformed in a resolution-dependenf manner. It is proposed to use a new transfer function concept to follow quantitatively, and in a resolution-dependent way, the effect of each subsequent surface modification step. This may be helpful, both for the quality control of product surfaces and for the systematic development of specific surface structures based on combinations of existing surface treatment methods. 

The attenuated reflectance technique presents an excellent example of how radiation at sample surface can enhance signal-to-noise ratio. Details of general optics and reflectance techniques can be found in the classic text (10). This technique is used extensively to determine differences between the structure of polymers in surface and bulk phases. Commercial accessories make these spectroscopic experiments easy to perform, although quantitative analysis of the data remains difficult. Examples of ATR applications include chemical composition analysis of polymers, surface orientation resulting from various processing methods, and chemical or thermal degradation of polymers. For samples such as powders or poorly defined surfaces, the diffuse reflectance technique can be used (11). In addition, the photoacoustic technique has been used to probe surface structure and multilayer structure commonly found in polymer laminates (17). In all these cases, optical effects can complicate analysis of infrared spectra. Nevertheless, these data have proven very useful in analytical applications. 

The correlation between the behaviour of U, U and v, t-curves found in Ref. [52] may be the basis for developing quantitative methods controlHng the hydrodynamic flux structure near the electrode surfaces, as well as methods for influencing the velocity of the heterogeneous processes by means of controlled changing of the hydrodynamic conditions of interfacial mass exchange. 

The method XPS is the most informative technique in studies of the physicochemical surface structure of pol miers [12]. It allows obtaining of information on the qualitative and quantitative chemical composition of surfaces virtually without damaging the studied objects. The thickness of the analyzed layer for pol5miers is no larger than 10 nm. However, for state-of-the-art instruments, the area resolution is 10 pm (when synchrotron radiation is used, a value of 2.5 pm [13] can be reached). 

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