Dispersive component of the surface free energy

London dispersive components of the surface free energy and surface enthalpy... 

The London dispersive component of the surface free energy, y, of a solid may be shown to be a predominant property for the prediction of behavior of nonpolar adsorbents such as polyolefins or of practically nonpolar adsorbents like some carbon materials (natural graphites and carbon fibers). In this section, we propose a simple approach for the determination of the ys using nonpolar probes such as n-alkanes in inverse GC at infinite dilution. We also discuss the evaluation of the London dispersive component of the surface energy (or enthalpy, / ), starting from the variation of the adsorption characteristics, of a series of long-chain n-alkanes molecules, with temperature. 

In the chromatographic process, three methods have been established for determining the London dispersive component of the surface free energy of a solid ... 

Dispersive Interactions. IGC was used to obtain the dispersive component of the surface free energy of the carbon fibers and of the polymers (Equation 2). These results are shown in Table II. 

Inverse gas chromatographic measurements may be carried out both at infinite dilution and at finite solute concentrations [1]. In the first case vapours of testing solutes are injected onto the colurtm and their concentrations in the adsorbed layer proceed to zero. Testing substances interact with strong active sites on the examined surface. The retention data are then converted into, e.g. dispersive component of the surface free energy and specific component of free energy of adsorption. In the second case, i.e. at finite solute concentrations, the appropriate adsorption isotherms are used to describe the surface properties of polymer or filler. The differential isosteric heat of adsorption is also calculated under the assumption that the isotherms were obtained at small temperature intervals. 

It is important to point out that for a flat surface (a = oo, d = constant) Eq.(16) reduces to Eq.(12), the original Gray s equation. Moreover, for a fixed molecule size, d, increases as the pore size, a, decreases, and reaches a maximum when the radius of the adsorbate becomes equal to the pore radius (hypothetical case). Equation (16) is thus a more general equation than Eq.(12), and permits the dispersion component of the surface free energy for porous and non- porous materials to be determined. 

Hydrocarbons are not intercalated into crystalline silicic acids. However, high adsorption enthalpies [157] and high values of the dispersive component of the surface free energy [158] in comparison with silica gels are indicative of a partial penetration of the alkyl chains into the interlays space at the edge regions. 

Interfadal tension between two fluid phases is a definite and accurately measurable property depending on the properties of both phases. Also, the contact angle, depending now on the properties of the three phases, is an accurately measurable property. Experimental approaches are described, e.g., in Refs. 8,60, and 63 and in Ref. 62, where especially detailed discussion of the Wilhehny technique is presented. Theories such as harmonic mean theory, geometric mean theory, and acid base theory (reviewed, e.g., in Refs. 8, 20, and 64) allow calculation of the soHd surface energy (because it is difficult to directly measure) from the contact angle measurements with selected test liquids with known surface tension values. These theories require introduction of polar and dispersive components of the surface free energy. 

The dispersive component ]/ of the surface free energy shows a continuous increase with the exposure time, regardless of the LER content. Differences between the studied films appear in the variation of the acid-base component (]/ ) of the surface free energy, as... 

Thus, according to this approach, developed by Schultz et al. [25], by measuring the net retention volume for various n-alkane probes and plotting RTIhVn versus a the dispersive component of the surface free energy can be determined... 

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