Lifshitz-van der Waals component

Chemical compound added to a base oil to improve oil quality as any substance that aids in the lubrication process at the rubbing interface by functionality other than viscosity. Intermolecular energy of attraction between the separate molecules making up a homogeneous liquid or solid. The energy consists of contribution from Lifshitz-van der Waals components in all cases. 

Van Oss et al. [103,108,109] combined y, yP and y into a single component, which they called the apolar or Lifshitz-van der Waals component (y ). The hydrogen bond (y ) and acid-base (y ) components were described by electron acceptor-electron donor (Lewis acid/base) interactions of the polar component (y/ ). The electron acceptor-electron donor parameters of the surface tension of a compoimd i are expressed as y (acidic term) and yf (basic term) according to y, = [108,109]. The total surface tension is... 

The dominating role of the Lifshitz-van der Waals component on the adhesion of particles (<50 xm) has also been shown on a semiconductor surface.These LW forces can increase with time due to particle and/or surface deformation, which increases the contact area. Micron-size particles can be held to surfaces by forces exceeding 100 dynes, which correspond to a pressure of 10 dyne/cm or more. Total forces of adhesion of micron-size particles exceed the gravitational force on the particle by factors greater than 10. Electrostatic forces only become important and predominant for particles larger than 50 xm. 

R. J. Good and M. K. Chaudhury, Theory of adhesive forces across interfaces (1) The Lifshitz-van der Waals component of interaction and adhesion, in Fundamentals of Adhesion (L. H. Lee, ed.). Chapter 3, Plenum Press, New York (1990). 

In a large part of the (current) literature the Lifshitz-van der Waals component (o, is simply termed dispersion component and the Lewis acid-base interactions (o ) are interpreted as polar interactions even though the material s dipole moments may be zero or the interactions originating from permanent dipoles are very small and can be easily associated with the dispersion part [6]. The misleading denominations go back to a historical misidentification of the acid-base interactions as polar interactions in the Owens-Wendt-Rabel-Kaelble [7-9] approach to calculate the IFT [6] (OWRK model). However, as an impact on the SFE calculation by this misinterpretation of this old theory occurs only when a monopolar base interacts with a monopolar acid, this nomenclature is still widely used. And here in this work we will also use the terms dispersion and po/ar interactions to differentiate the two major contributions to SFE, ST, and IFT. For a detailed discussion of the use of contact angles in determining SFE of solids and other methods of determining SFE, see Etzler [10]. 

The dominating role of the Lifshitz-van der Waals component on the adhesion of particles (<50 pm) has also been shown on a semiconductor surface.These LW forces can increase with time due to particle and/or surface deformation, which increases the contact area. Micron size... 

The surface tension component method assumes that surface tension can be partitioned into different components, which address different intermolecular interactions individually. The overall surface tension will be the sum of all the components according to the linear free energy relationship. In the original Fowkes method [14], only the dispersion interaction is considered. The component method has been subsequentiy extended to include polar component and later divided the polar component into dipolar interaction and H-bonding interaction. The vOCG model appeared as a refined version of the surface tension component methodology. It assumes the existence of both additive and nonadditive components. The Lifshitz-van der Waals component (/ ) is additive, and the electron donor and acceptor components (7 and 7" ) are nonadditive. The solid surface tension (7sv) can be calculated by using three Uquids with known y, y and y values. Since this is a semiempirical approach, the calcu-... 

Good, van Oss, and Caudhury [208-210] generalized this approach to include three different surface tension components from Lifshitz-van der Waals (dispersion) and electron-donor/electron-acceptor polar interactions. They have tested this model on several materials to find these surface tension components [29, 138, 211, 212]. These approaches have recently been disputed on thermodynamic grounds [213] and based on experimental measurements [214, 215]. 

These equations result from assuming that the total surface energy can be split into the sum of components associated with different types of bonding, for example dispersion plus polar yP (Eqs. 14 and 15), or Lifshitz-van der Waals... 

Table VIII. Comparison of Lifshitz—van der Waals Potentials to Residual Free Energy Components after Correcting for Double Layer Repulsion...

From the surface thermodynamics point of view, the treatment proposed by van Oss et a . (II, 13) gave the possibility of a quantitative estimation of solvation forces, either of hydrophobic or hydrophilic nature (see Sec. II). In this approach, the free energy of interaction (A(7) between the particles consists of three components electrostatic, Lifshitz-van der Waals, and acid-base ... 

In other words, the total potential energy of nanoparticle-liquid interactions is the sum of a Lifshitz-van der Waals interaction (y ), which means the surface free energy (dipole-dipole and dipole-induced dipole interaction), and Lewis acid-base interaction (y ). The Lewis acid-base interaction (y ) for the component i is simply calculated by the geometric mean of electron acceptor (y ) and donor (y ) ... 

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 article on Surface energy components describes how surface energies of solids and thence the work of adhesion between adhesive and substrate could be calculated from an assumption that the surface energy is composed of the sum of a dispersion and polar component (Eqn. 9 therein). Practical measurements of surface tensions of liquids and of contact angles of liquids on solids were involved. In a similar way, solid surface energies and works of adhesion can be obtained from the assumption (Eqns. 3 and 4 above) that surface energy is made up of the sum of a Lifshitz-van der Waals and an acid-base component. The term is obtained using non-polar liquids in exactly the same way as the dispersion components, y, were obtained. This article is concerned with expressions that can be used to represent acid-base interactions and which can then be used in equations such as 3 and 4 and those derived from them. 

Considerations, such as these, have lead Good and others to use the term Lifshitz-van der Waals forces when referring in the context of Contact angles and interfacial tension and Surface energy components to weak interactions between molecules. 

Taking cognizance of the considerations discussed under Lifshitz-van der Waals forces, the van der Waals force component to surface energy has often been written in recent literature as Y f where LW stands for Lifshitz-van der Waals. y represents ail the van der Waals force interactions, that is, in the earlier terminology, dispersion plus polar. Its contribution to the lowering of interfacial tension can be represented by a geometric mean relationship, see Eqn. 4,... 

By definition, taking the fluid to be water, if AG121 < 0, then the entity is hydrophobic and if AG121 > 0, then the entity is hydrophilic. The interfacial surface tension depends on the single-substance surface tensions of the interacting entities, Yi and y2- These single-substance tensions have an apolar (Lifshitz-van der Waals) and a polar (Lewis acid/base) component ... 

The calculations with Equation 11.23 and Table 11.3 are in reasonably good agreement with the reported values for the Lifshitz-van der Waals surface tension component in the literature [4-6,28]. As an example, the y calculated from Equation 11.23 for methanol, ethanol, glycerol, and water are 17.23, 18.03, 31.97, and 21.13 mN/m, respectively, while the corresponding reported values [28] are 18.5, 20.1, 34.0, and 21.8 mN/m, respectively. Having the partial surface tensions of pure solvents, we may now proceed to the next step and propose a method for the surface-tension characterization of polymers and solid surfaces. 

When a solid surface involves both the Lifshitz-van der Waals and acid-base interactions, the total work of adhesion should be the sum of the following two components ... 

Fowkes [15-16] suggested that surface free energy and thus the work of adhesion could be considered as a sum of components resulting from various types of intermolecular interactions. At present, it is conventional to express the work of adhesion as a sum consisting of a term for Lifshitz-van der Waals interactions and second term resulting from Lewis acid-base interactions [13]. Frequently, Lifshitz-van der Waals interactions are dominant. 

It has been further generalized that all of the Lifshitz-van der Waals (LW) components follow the same rule thus... 

Wu, W. Giese, R.F. van Oss, C.J. Evaluation of the Lifshitz-van der Waals/acid-base approach to determine surface tension components. Langmuir, 1995, 11, 379-382. 

Fowkes was the first to propose this approach in the 60s by writing the total interaction as having three components the Lifshitz—van der Waals dispersive d), the polar (/>), and the hydrogen bond (/ ) terms. The expression for the surface tension... 

Kwok D. (1999) The usefulness of the Lifshitz-van der Waals/acid-base approach for surface tension components and interfacial rensions. Colloids Surfa-Physicochem Eng Asp 156 191-200. 

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