Polarity of solid surface

To rate the polarity of solid surfaces from their heats of immersion in simple organic liquids having different peripheral dipole moments. For the first time, this technique allows an experimentally derived number to be put on the average force field emanating from solid surfaces. 

Determination of the polarity of solid surfaces 135 Study of surface modification 137 Assessment of the site-energy distribution 138 Assessment of structural modifications of the adsorbent 139 Assessment of microporosity 139 Assessment of surface area 139... 

This commentary on the current status of research on heats of immersion begins where our review written in 1958 concludes [6]. The classification of heats of immersion of solids into liquids as a function of precoverage is expanded to include two new types of curves. Several difficulties in heat of immersion research are discussed. Then, current applications of heats of immersion to determine the average polarity of solid surfaces, heterogeneities on solid surfaces, wetting by surfactants, hydrophilicity of solid surfaces, and thermodynamics of the specific interaction of molecules from solution onto solid surfaces are described. 

The average polarity of solid surfaces can be estimated from heats of immersion into selected liquids, usually n-butyl derivatives possessing... 

Figure 3, Determination of polarity of solid surface (rutile)...

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

Geometric mean approximation Dispersive and polar components of solid surface energy are found by solving yiv(l +COS0) = 2(y,Xf + 2(y Yl S An extension of GGF equation ysa predicted is significantly higher than the critical surface tension. [84]... 

The sorption of water vapor onto nonhydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to nonpolar solids like carbon or polytetrafluorethylene (Teflon) [21], but it sorbs to a greater extent to more polar materials such as alkali halides [34-37] and organic salts like sodium salicylate [37]. Since water is only sorbed to the external surface of these substances, relatively small amounts (i.e., typically less than 1 mg/g) of water are sorbed compared with hydrates and amorphous materials that absorb water into their internal structures. 

The extent to which surface tension can be controlled by fluoroalkyl-containing coupling agent type treatments is summarized in Table 1. Its purpose is to simply illustrate the range of control possible detailed comparisons are unwarranted because of differences in sample preparation and choice of substrate, data acquisition and treatment. Some of the critical surface tensions (crc) are obtained with -alkanes, some with other liquids. Some of the dispersion force components (of) and polar components (of) of solid surface tension are derived by use of different equations. The reader is referred to the key references in Table 1 for full details. 

For a selection of non-polar liquids on a given solid, it follows that 0 should decrease as yLG decreases and become zero below a certain value of tlg- Zisman78 has named this value of yLG the critical surface tension, yc, for the solid. Critical surface tension is a useful parameter for characterising the wettability of solid surfaces (see Table 6.1). 

The n transition energy of a spiropyran zwitterion of the type described in Section 4.4.2 [(27a) (27b)] has been used by de Mayo et al. to characterize the polarity of solid oxide surfaces such as that of silica gel [217]. 

Interfaclal polarization see potential difference, x Interfaclal potential Jump xY, see potential difference, x interfaclal potentials 1.5.5, 3.9 interfaclal pressure see surface pressure interfaclal science (first review) 1.1.2, 1.1.3 interfaclal tension, surface tension I.1.4(intr.), 1.1.25, fig. 1.1.16 measurement 1.1.11,1.2.5,1.2.96, 3.139 of curved interfaces 1.2.23. 1.6d of films 1.95ff of solid surfaces 1.2.24... 

The sorption of water vapor onto non-hydrating crystalline solids below RHq will depend on the polarity of the surface(s) and will be proportional to surface area. For example, water exhibits little tendency to sorb to non-polar solids like carbon or polytetrafluoroethylene... 

In the case of polymer molecules, the silica surface can be regarded to be deactivated reliably enough only with respect to large polar molecules, whereas small polar molecules (like methyl and ethyl alcohols) can access the active sites of solid surface, in spite of the screening [34]. 

Zettlemoyer, A.C., Chessick, J.J., and HoUabaugh, C.M. (1958). Estimation of the surface polarity of solids from heat of wetting measurements. Phys. Chem., 62, 489-90. Morimoto, T. and Suda, Y. (1985). Heat of immersion of zinc oxide in organic liquids. 1. Effect of surface hydroxyls on the electrostatic field strength. Langmuir, 1, 239—43. 

To change the polarity of the surface of the solid phase so nonpolar compounds can be separated. Dimethyldichlorosilane is added to the solid phase to form a reactive chlorosilane on former -OH groups. Then water is added followed by a long chain dichlorosilane, and finally endcapped. 

The beneficial effects of solid surfaces on the rates of bromination reactions were observed as eai ly as 1923 [4-6], The polarity of the glass surface was found to enhance the rates of bromination of ethylene. Halogenation reactions over zeolite catalysts have been reviewed [1]. A summary of halogenations over non-zeolite (until mid-1999) and zeolite (1995-mid 1999) catalysts is given in Table 1. 

In the previous section the adsorption concept was entered of adsorption molecular electrostatic potential and it was remarked that the first and rather acceptable approximation could be obtained by its help for constructing hydrate cover of any type of solid surface. However, within the framework of notions on MESP it is also possible to predict some other important properties of adsorption complexes of polar molecules on silica surface. Thus, it was shown in [ 137] that hydrophility of the hydroxylated surface of silicion dioxide could be explained by availability of local minima of the p potential within the subsurface region created by the atoms of surface functional groups and solid substrate. Here in water this approach was applied to explain adsorption properties of completely chlorinated, aminated, and hydrogenated surfaces [128]. 

The basic thesis of Zisman s work was that the contact angle of a liquid on a solid reflects in some way the chemical constitution of the solid surface. He took the point of view Langomuir that the range of forces acting at the surface of a non-polar solid are short of the order of a few nanometers. Therefore, the contact angle must reflect the properties and in some fashion the actual composition of the surface of the solid. In this context, contact angle measurements are highly sensitive to the outer most chemical characteristics of solid surfaces. 

E. Reflectance Measurements of Solid Surfaces Using Polarized Light. 241... 

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