Molecular van der Waals interaction

Phase equilibria of systems containing oppositely charged ionic surfactants have been the subject of extensive experimental and theoretical investigations [39-61]. Competition between various molecular interactions (van der Waals, hydrophobic, electrostatic, hydration forces, etc.) may result in a variety of micro-structures, mixed micelles, vesicles, and catanionic surfactant salts. Mixing aqueous solutions of anionic surfactant with an equivalent amount of cationic surfactant (alkyl chains with more than eight atoms) results in precipitation of... 

In molecular mechanics, van der Waals forces are thought to inlliieiiee atoms that are wnthiii the same molecule but are not connected by chemical bonds. They are sometimes called 1-4 interactions, implying that a chemical bond does not exist between atoms 1 and 4 but one does exist between atoms 2 and 3... 

Although the diffusion mechanism can be seen as mechanical but occurring at molecular dimensions, van der Waals intermolecular interactions and conformational entropic energy provide an additional mechanism that increases adhesion [62]. It is interesting to note the analogy that exists between this mechanism at the molecular level with the adherence, adhesion and viscoelastic deformations concept applied for a macroscopic adhesive. 

There are three types of nonbonding intermolecular interaction dipole-dipole interactions, van der Waals forces and hydrogen bonding. These interactions increase significantly as the molecular weights increase, and also increase with increasing polarity of the molecules. 

Israelachvili, J. N., Intermodular and Surface Forces, 2d ed., Academic Press, New York, 1991. (Graduate and undergraduate levels. An excellent source for the relation between molecular-level van der Waals interactions and macroscopic properties and phenomena such as surface tension, cohesive energies of materials, adhesion, and wetting. Also discusses direct measurement of van der Waals forces using the surface force apparatus.)... 

Acidic pesticides such as 2,4-D, 2,4,5-T, picloram, and dinoseb can ionize in aqueous solutions forming anionic species (Saltzman and Yaron, 1986). Sorption of these pesticides on soils has also been correlated with soil organic matter content (Hamaker et al., 1966), and in their anionic form they can be sorbed on soils, clays, and amorphous materials at low pH. The mechanisms of sorption for these compounds are proton association and, for the molecular form, van der Waals sorption (Saltzman and Yaron, 1986). Hydrogen bonding and electrostatic interactions are other possible mechanisms for sorption. 

Chiral separations generally rely on the formation of transient diastereomeric complexes with differing stabilities. Complexes are defined as two or more compounds bound to one another in a definite structural relationship by forces such as hydrogen bonding, ion pairing, metal-ion-to-ligand attraction, n-acid/ n-base interactions, van der Waals attractions, and entropic component desolvation. In the following sections, the most important types of molecular interactions in chiral separations are discussed. 

The hydrophobic effect is an aggregate phenomenon, distinguished from all other molecular forces (e.g., covalent, ionic, dipolar, hydrogen bonding, 7i interactions, van der Waals, and London forces) in that it arises from the collective behavior of many molecules by disruption of the hydrogen-bonded structure of water. 

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