Dispersive components of surface free energy

Method based on the quantity, a(yl)1/2 of the London dispersive component, > of surface free energy multiplied by cross sectional area, a, of nonpolar probes, such as n-alkanes [87,125]. 

The work of adhesion increases as the dispersive component of surface free energy increases. Table 5.11 gives the values of the dispersive component available in the literature for different fillers. 

Densification of carbon black by compression increases the dispersive component of surface free energy. This process is initially not proportional to density, but after some threshold value at around 0.7 g/cm the dispersive component has a linear... 

The dispersive component of surface free energy 7 may be calculated from Eq.(ll) with the use of experimentally determined AGcHj [23-47]. 

Surface characteristics of the series of commercially available aluminas with the use of IGC were reported by Papirer et al. [34]. Values of the dispersive component of surface free energy 7 varied from 65 to 100 mJ/m. Authors determined also Kd and Ka values. The variation of the electron donor parameter Kd was almost negligible (2.1-2.7), while Ka parameter increased from 5.6 to 9.9 units. The significant changes for acidity were related to the Si02 content. Acidity parameter, Ka, reached a constant value for a Si02 content of about 1000 ppm. However, AN and DN were taken from Gutmann s proposal... 

Table 7 Dispersive Components of Surface Free Energy of Adsorption and Related Thermodynamic Properties of MSX, SX-I, and SX-II...

Dispersive Component of Surface Free Energy and Related Thermodynamic Parameters... 

A plot of RTln Fn against u(yL ) according to Eq. (30) yields a linear slope of 2A(ys), from which the dispersive component of surface free energy of adsorption, yP, can be determined (60). 

Table 7 contains some values of the polar and dispersive components of surface free energy [57] for some polymers obtained using the geometric and harmonic mean methods. It can be seen that they are in good agreement. 

This represents the dispersion component of surface free energy, taken from reference 66 Calculated using extended Fowkes equation to two components, taken from reference 68 from reference 64... 

Dispersive component of surface free energy of the liquid probe 7 Dispersive component of the surface free energy of the solid Vj Retention volume and C A constant. 

Figure 5.24 shows the effect of oxidation on dispersive and polar components of surface free energy. Carbon fibers were exposed to plasma treatment in the presence of various ratios of CF4 and O2. The untreated sample and the samples exposed to a substantial concentrations of oxygen show increase in the polar component. Fligh concentrations of CF4 gas reduced its dispersive component and converted the surface to a PTFE-like material as confirmed by XPS studies. 

Polar probes have both dispersive and specific components of surface free energy of adsorption. The specific component of surface free energy of adsorption (AGa is determined by subtracting the dispersive contribution from the total free energy of adsorption, and can be obtained from the vertical distance between the alkane reference line [Eq. (30) Figure 21] and the polar probes of interest according to the following equation (60) ... 

In these equations y is the dispersion force component and yP the other polar force components of surface free energy (y = -l- yP). Equation (59.6) was introduced by... 

Table 59.3 is based primarily on the Zisman critical surface tension of wetting and Owens and Wendt approaches because most of the polymer data available is in these forms. The inadequacies of equations such as Eq. (59.7) have been known for a decade, and newer, more refined approaches are becoming established, notably these of van Oss and coworkers [24]. A more limited number of polymers have been examined in this way and the data (at 20 °C) are summarized in Table 59.4. is the component of surface free energy due to the Lifshitz-van der Waals (LW) interactions that includes the London (dispersion, y ), Debye (induction), and Keesom (dipolar) forces. These are the forces that can correctly be treated by a simple geometric mean relationship such as Eq. (59.6). y is the component of surface free energy due to Lewis acid-base (AB) polar interactions. As with y and yP the sum of y and y is the total solid surface free energy, y is obtained from... 

Dispersion force component of surface free energy yf mj - 62 9 (5)... 

The dispersive component of the vaporization energy near a solid surface is approximately given by Eq. (18). The vaporization energy is the energy required to remove a molecule from the liquid without leaving a hole behind. The free volume needed for a flow unit to make a transition into the flow-activated state is less than the size of the entire molecule. It... 

Investigations of surface free energy (SFE) of controlled porosity glasses and silica gels carried out more recently showed certain similarity in the properties of bare materials and important differences caused by thermal treatment [49-56]. Dispersive interactions expressed as dispersive component of SFE (7 ) and polar interactions expressed as polar component of SFE (7 ) measured by means of hexane and toluene respectively are similar for both materials. The average value of 7 for silica gel equals 35.6 mj/m and for CPG 35.0 mJ/m. The mean values of 7P for silica gel and CPG are 159.8 mj/m and 159.2 mJ/m, respectively. The thermal treatment of both materials leads to a small increase of dispersive interactions and simultaneously causes a significant drop of polar interactions. 

Authors of Ref. [49] proved that the variation of the term RT In Vn as a function of the molar deformation polarization of n-alkanes Pdp is a straight line which slope equal to C Pds is proportional to the surface ability for dispersive interactions. AG = 0 is defined in the same way as in the case of Saint Flour-Papirer s method. However, in this procedure AG = 0 values are always positive while in approach [48] the negative values of the specific component of the free energy of adsorption were observed. Later, Donnet et al. [29] observed that their earlier proposal (i.e. that from Ref.[49]) based on the fundamental London equation gives only a first approximation of the ionization energy of a molecule. They proposed to use Eq.(15) in the form ... 

If RTlnV is plotted versus a(yL ) for a series of alkanes a straight line results and the dispersive contribution of the surface energy can be calculated from the slope. If polar probe molecules are injected, specific interactions can be determined. In the above-mentioned plot, points representing a polar probe are located above the straight line. The distance is equal to the specific component of the free energy JG /. (equation 5). 

All other polar probes exhibit higher net retention volumes, En. and the difference between their net retention volume and that of the n-alkanes for the same value of the dispersive component of surface energy leads to the value of the free energy of desorption, AGjp, corresponding to the specific acid-base interaction, expressed as ... 

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