Van der Waais interactions

The nature of these two phases helps lo throw light on the melal-nonmetal transition. For example there has been much speculation that hydrogen molecules at suflicienlly high pressure, such as those occurring on the planet Jupiter, might undergo a transition to un "alkali metal The fundamental transition is one of a dramatic change of the van der Waais interactions of H2 molecules into metallic cohesion. ... 

The so-called London dispersion or van der Waais interactions are those between molecules that have neither a net charge nor a permanent dipole moment. This interaction is essentially due to the interactions between a transient electrical dipole in one molecule and its induced electrical dipole in the other molecule. TTiis type of electrical interaction plays an important role in biological systems (e.g., in surface tension, stability of biological membranes, condensation properties, adhesion and fusion of biological cell membranes, enzyme-substrate recognition, etc.). 

In 1873 van der Waais pointed out that real gases do not obey the ideal gas equation PV = RT and suggested that two correction terms should be included to give a more accurate representation, of the form (P + ali/) V - b) = RT. The term a/v corrects for the fact that there will be an attractive force between all gas molecules (both polar and nonpolar) and hence the observed pressure must be increased to that of an ideal, non-interacting gas. The second term (b) corrects for the fact that the molecules are finite in size and act like hard spheres on collision the actual free volume must then be less than the total measured volume of the gas. These correction terms are clearly to do with the interaction energy between molecules in the gas phase. 

Hull and Kitchener (2) measured the rate of deposition of 0.3- an-diameter polystyrene latex particles onto a rotating disk coated with a film of polyvinyl formaldehyde. In electrolytes of high ionic strength (where the double-layer repulsion is negligible), they found close agreement between experiments and the prediction of Levich s boundary-layer analysis (Eq. 3]), indicating that a diffusion boundary layer exists and that its thickness is large compared to the domain of van der Waais and hydrodynamic interactions. These are neces-... 

Conventional van der Waais Mixing Rules with a Single Binary Interaction Parameter (IPVDW Model)... 

This equation introduces the binary interaction parameter in a manner similar to that of eqn. (3.3.6) of the van der Waais one-lluid mixing rule. Next, the following modified form of the NRTL equation was used for the excess free-energy term ... 

Electrostatic interactions cannot account for all of the non-bonded interactions in a system. The rare gas atoms are an obvious example all of the multipole moments of a rare gas atom are zero and so there can be no dipole-dipole or dipole-induced dipole interactions. But there clearly must be interactions between the atoms, how else could rare gases have liquid and solid phases or show deviations from ideal gas behaviour Deviations from ideal gas behaviour were famously quanfatated by van der Waais, thus the forces that give rise to such deviations are often referred to as van der Waais forces. 

Figure 13.1 liiustration of interaction energy curves for two oii dropiets coated with a p-casein adsorbed iayer. The tradi-tionai interaction energy curve (Vj) represents the summation of the van der Waais attraction energy curve Vp) with the... 

Nonbonded interactions are the forces between atoms that aren t bonded to one another they may be either attractive or repulsive. It often happens that the shape of a molecule may cause two atoms to be close in space even though they are separated from each other by many bonds. Induced-dipole/induced-dipole interactions make van der Waals forces in alkanes weakly attractive at most distances, but when two atoms are closer to each other than the sum of their van der Waals radii, nuclear-nuclear and electron-electron repulsive forces between them dominate the Evan der waais term-The resulting destabilization is called van der Waals strain. 

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