Dipolar interactions Debye

Dipolar Interactions London, Keesom, and Debye Forces... 

Dispersion Forces The dipolar interaction forces between any two bodies of finite mass, including the Keesom forces of orientation among dipoles, Debye induction forces, and London forces between two induced dipoles. Also referred to as Lifshitz—van der Waals forces. 

The solution detennines c(r) inside the hard core from which g(r) outside this core is obtained via the Omstein-Zemike relation. For hard spheres, the approximation is identical to tire PY approximation. Analytic solutions have been obtained for hard spheres, charged hard spheres, dipolar hard spheres and for particles interacting witli the Yukawa potential. The MS approximation for point charges (charged hard spheres in the limit of zero size) yields the Debye-Fluckel limiting law distribution fiinction. 

Relaxation processes are probably the most important of the interactions between electric fields and matter. Debye [6] extended the Langevin theory of dipole orientation in a constant field to the case of a varying field. He showed that the Boltzmann factor of the Langevin theory becomes a time-dependent weighting factor. When a steady electric field is applied to a dielectric the distortion polarization, PDisior, will be established very quickly - we can say instantaneously compared with time intervals of interest. But the remaining dipolar part of the polarization (orientation polarization, Porient) takes time to reach its equilibrium value. When the polarization becomes complex, the permittivity must also become complex, as shown by Eq. (5) ... 

In certain circumstances, it may be necessary to distinguish between the different types of interactions. This can be performed in several ways (Barton, 1983 Van Krevelen, 1990). The most usual method is to make a distinction between dispersion (London), dipolar (Debye Keesom) and hydrogen-bonding components, each one being characterized by its contribution to CED and the corresponding solubility parameter, 8d, 8p, 8h, respectively, such that 8 = (8d + 8p + 8j )1/2. 

Complex dielectric susceptibility data such as those in Figure 15.6 provide a detailed view of the dynamics of polar nanodomains in rls. They define relaxation frequencies, /, corresponding to the e (T) peak temperatures Tm, characteristic relaxation times, r = 1/tu (where uj = 2nf is the angular frequency), and a measure of the interaction among nanodomains as represented by the deviation of the relaxation process from a Debye relaxation. Analysis of data on pmn and other rls clearly shows that their dipolar relaxations cannot be described by a single relaxation time represented by the Debye expression... 

It has to be emphasized that more refined approaches have been established, in particular by Van Oss and coworkers (1994). They introduced the so-called Lifschitz-Van der Waals (LW) interactions. These interactions include the dispersion or London forces ( / ), the induction or Debye forces (yD) and the dipolar or Keesom forces (, K), so that ... 

Van der Waals forces arise from dipole-dipole interactions. In a dipolar molecule, there is a separation of positive from negative charge. For example, if the molecule contains charges -Fq and —q separated by a distance vector r, then the molecule has a dipole moment of u = rq. Dipolar moments are often measured in units of the Debye D, where 1 D = 3.336 X 10 coulomb-meter. While alkanes have no permanent dipole moments,... 

In solvents of low dielectric constant, where the Coulomb interactions are particularly strong, electrical conductance and dielectric spectra suggest that the ion distribution involves dipolar ion pairs, which then interact with the free ions and with other dipolar pairs. The ion pairs cause an increase of the dielectric constant, which in turn stabilizes the free ions, thus leading to redissociation at high salt concentrations. Extending the approach of Debye-Hiickel and Bjerrum, theory accounts for ion pairing, ion-ion pair and ion pair-ion pair interactions and rationalizes the basic features of the ion distribution in accordance with experiments and MC-simulations. 

Debye interactions interactions between dipolar molecules and induced dipolar molecules (rotating)... 

Debye derived a more general expression from Equation (59) for the interactions between dipolar molecules and induced dipolar molecules (rotating) in 1920. He found that when induction takes place, the pair potential energy between two different dipolar molecules each possessing permanent dipole moments of pi and p2 and polarizabilities a, and ah can be expressed as,... 

As detailed in Chapter 2, van der Waals interactions consist mainly of three types of long-range interactions, namely Keesom (dipole-dipole angle-averaged orientation, Section 2.4.3), Debye (dipole-induced dipolar, angle-averaged, Section 2.5.7), and London dispersion interactions (Section 2.6.1). However, only orientation-independent London dispersion interactions are important for particle-particle or particle-surface attractions, because Keesom and Debye interactions cancel unless the particle itself has a permanent dipole moment, which can occur only very rarely. Thus, it is important to analyze the London dispersion interactions between macrobodies. Estimation of the value of dispersion attractions has been attempted by two different approaches one based on an extended molecular model by Hamaker (see Sections 7.3.1-7.3.5) and one based on a model of condensed media by Lifshitz (see Section 7.3.7). 

This differs from the dipolar fluid case [A i f(0)= — (e- ) /3yEp (cf. Section II.A)] and results from the Debye screening of the dipole-dipole interactions. Combining (5.20b), (5.21b), (5.23), and (5.24), we obtain, when... 

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... 

The first type is the so-called Keesom interaction between molecules having a permanent dipolar moment such as water or formamide, as well as the Debye interaction between molecules with permanent dipolar moments and molecules with induced dipolar moments. These two kinds of interaction are directional and thus imply a specific orientation of the molecules, and they are strong interactions at about a few kilocalories per mole. For example, these may be the interactions on the polar-group side of the surfactant, such as between a sulfate group and water, or a carboxylate group and the next molecule in a similar molecular group. 

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