Van der Waals forces dispersion

Table A.4.1 Attractive Forces at Interfaces-surface Energy, y, and London-van der Waals Dispersion Force Component of Surface Energy, y(L) a>...

FIG. 10.7 Direct measurements of van der Waals dispersion forces. The measurements correspond to the force between two flat (mica) surfaces separated by a distance d. The line shown is the theoretical expression for unretarded van der Waals force. The figure shows that the unretarded expression describes the measurements sufficiently accurately for d about 6.5 nm or less. (Redrawn with permission of J. N. Israelachvili and G. E. Adams, J. Chem. Soc., Faraday Trans. 1, 78, 975 (1978).)... 

Curve P represents the physical interaction energy between M and X2. It inevitably includes a short-range negative (attractive) contribution arising from London-van der Waals dispersion forces and an even shorter-range positive contribution (Born repulsion) due to an overlapping of electron clouds. It will also include a further van der Waals attractive contribution if permanent dipoles are involved. The nature of van der Waals forces is discussed on page 215. 

Clarke and co-workers developed a model to calculate the thickness of the amorphous film observed in polycrystalline ceramics.37,38 The model is based on a force balance between an attractive van der Waals dispersion force that acts across the grain boundaries, any capillary forces present, and repulsive disjoining forces (such as steric forces and electrical double-layer forces) in the amorphous film.37,38 The repulsive steric force is based on the... 

Van der Waals postulated that neutral molecules exert forces of attraction on each other which are caused by electrical interactions between dipoles. The attraction results from the orientation of dipoles due to any of (1) Keesom forces between permanent dipoles, (2) Debye induction forces between dipoles and induced dipoles, or (3) London-van der Waals dispersion forces between fluctuating dipoles and induced dipoles. (The term dispersion forces arose because they are largely determined by outer electrons, which are also responsible for the dispersion of light [272].) Except for quite polar materials the London-van der Waals dispersion forces are the more significant of the three. For molecules the force varies inversely with the sixth power of the intermolecular distance. 

Figure S.3 Potential energies of interaction between two colloidal particles as a function of their distance of separation, for electrical double layers due to surface charge (VolK London-van der Waals dispersion forces (V ), and the total interaction (VT). From Schramm [426], Copyright 2003, Wiley.

It is true that all molecular and atomic forces ultimately find their root in the mutual behavior of the constituent parts of the atoms, viz., the nuclei and the electrons. They may theoretically all be derived from the fundamental wave equations. It is, however, convenient, as in other branches of physics and chemistry, to treat the various forms of mutual interaction of atoms as different forces, acting independently. We shall therefore follow the usual procedure and treat such forces as the nonpolar van der Waals (dispersion) forces, the forces of the electrostatic polarization of atoms or molecules by ions or by dipoles, the mutual attraction or repulsion Coulomb forces of ions and of dipoles, the exchange forces leading to covalent bonds, the repulsion forces due to interpenetration of electronic clouds, together with the Pauli principle, etc., all as different, independently acting forces. 

B. M. Axilrod and E. Teller, "Interaction of the van der Waals type between three atoms," J. Chem. Phys., 11, 299-300 (1943) see also the pedagogical article by C. Farina, F. C. Santos, and A. C. Tort, "A simple way of understanding the non-additivity of van der Waals dispersion forces," Am. J. Phys., 67, 344-9 (1999) for the step from two-body to three-body interactions. 

Interactions between crossed cylinders of mica in air, uncoated or coated with fatty acid monolayers, are described in J. N. Israelachvili and D. Tabor, "The measurement of van der Waals dispersion forces in the range 1.5 to 130 nm," Proc. R. Soc. London Ser. A, 331, 19-38 (1972). An excellent review of this and related work is given in J. N. Israelachvili and D. Tabor, Van der Waals Forces Theory and Experiment, Vol. 7 of Progress in Surface and Membrane Science Series (Academic Press, New York and London, 1973). Later reconciliation of theory and experiment required taking note of cylinder radius L. R. White, J. N. Israelachvili, and B. W. Ninham, "Dispersion interaction of crossed mica cylinders A reanalysis of the Israelachvili-Tabor experiments," J. Chem. Soc. Faraday Trans. 1, 72, 2526-36 (1976). 

The interaction potentials described in previous sections for adsorbing homopolymer and terminally anchored layers in good solvents clearly indicate the ability of polymers to stabilize colloidal dispersions against flocculation due to van der Waals dispersion forces. Indeed, the practice preceeded the analyses by centuries in some cases and decades in others, since the use of adsorbing polymers dates to ancient times, and block copolymer stabilizers emerged from industrial laboratories in the 1960s (Napper, 1983). 

E) There are more Van der Waals (dispersion) forces between nonpolar molecules that are greater in mass. 

E All of these hydrocarbons are nonpolar and will be affected by Van der Waals (dispersion) forces. As the mass of the nonpolar molecules increases, so do the dispersion forces. This is why the wax (molar mass of 282), C20H42, is a solid. 

In these models, the method consists of (i) assuming that a certain type of interaction such as van der Waals dispersion forces (Didier and Jupille 1994, Naidich 1981) or image forces (Stoneham et al. 1995) is predominant at metal/oxide interfaces, (ii) calculation of the adhesion energy resulted from these... 

The final step in the development process involves the transfer of the toner particles from the carrier beads to the photoreceptor surface. The forces that bind the toner to the beads are electrostatic and van der Waals dispersion forces. Development thus requires that the forces due to the fields associated with the latent image exceed the forces that holds the toner to the carrier. For a discussion of processes by which toner particles are transferred from carrier beads to photoreceptor surfaces, see Schein (1975), Hays (1977, 1978), and Schein and Fowler (1985). For a discussion of the roles of van der Waals and electrostatic forces, see Gady et al. (1996). 

Adsorption by dispersion forces, i.e., London-van der Waals dispersion forces acting between adsorbate and adsorbent... 

L) values for water and mercury have been determined by measuring the interfacial tension of these liquids with a number of liquid-saturated hydrocarbons. The inteimolecular attraction in the liquid hydrocarbons is entirely due to London-van der Waals dispersion forces for all practical purposes. Yjd was derived from contact angle measurements. 

The intermolecular effects generally involve van der Waals dispersion forces, hydrogen bonding and dipole-dipole interactions61. Since 5(19F) values are also dependent on the sample concentration50, these were usually extrapolated to infinite dilution when searching for dependencies between 5(19F) and cr49,50 52 62. 

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