Free dispersion component

By the geometric-mean method [106] the total surface free energy (y ), the polar (yl") and dispersive component (yf) of both systems were calculated (Fig. 9.10 e,f). 

In the early 1960s, Fowkes [88,89] introduced the concept of the surface free energy of a solid. The surface free energy is expressed by the sum two components a dispersive component, attributable to London attraction, and a specific (or polar) component, y p, owing to all other types of interactions (Debye, Keesom, hydrogen bonding, and other polar effects, as similarly described before in Sec. II. C... 

As described before, it is generally accepted that the intermolecular adsorption of Gibbs free energy of an adsorbate-adsorbent system have been generally ascribed by the sum of two terms [88,89] the London dispersive component, —AG, and the specific component, — AG P, as... 

The relation shown above reveals that the London dispersive component of the Gibbs free energy of a solid is a function of the characteristics of liquid, (Avl)1/2 oco.l, [or, a function of asince hv is also a function of ao in Eq. (8)], as shown in Fig. 7. 

Conversely, this equation allows us to calculate the London dispersive component of the adsorbate-adsorbent interaction for a given liquid when the quantity (Avl)1/2 ao,L is defined as a characteristic of the probe considered, as listed in Table 6 from the basis of the polarizability of molecules (in Table 3). For polar probes, the additional or specific component of the Gibbs free energy, — AG P in Eq. (50) resulting from polar interactions is then determined by the distance between the experimental points A and B of same abscissa on the n-alkane lines as illustrated in Fig. 7. 

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]. 

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. 

Also, Eq. (32) may be rewritten in terms of the London dispersive component of adsorption Gibbs free energy, —AG, ... 

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

When considering the addition of a bioactive to food, it is useful to classify them as oil-soluble (e.g., polyunsaturated fatty acids, carotenes, lycopene), water-soluble (e.g., anthocyanins, proteins and peptides), or water/oil dispersible components (e.g., probiotics). Bioactives may be added directly to food if they are in a compatible format with the food matrix and provided their direct addition does not impact negatively on food quality or the bioavailability of the bioactive. When the solubility in a food matrix is limiting, its hydrophilicity/lipophilicity may be modified to enable improved incorporation. An example is the conversion of free plant sterols to fatty acid esters in order to make them more oil-soluble and readily incorporated into spreads (Deckere de and Verschuren 2000). 

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. 

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... 

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. 

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. 

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... 

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. 

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. 

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

The specific component of free energy of adsorption is generally determined by the subtraction the dispersive component from the total free energy of adsorption. Several procedures of the calculation of the specific component have been presented in the literature. The differences between the respective procedures lie in the choose of the reference state of the adsorbed molecule. 

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... 

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