Dispersion bond Waals

The van der Waals or dispersive bond is the weakest. It accounts for inter-molecular forces, which represent only a small contribution to bonds in materials except for glues and liquid crystals. 

Van der Waals or dispersion bonding occurs between non-polar molecules when a fluctuating dipole in one molecule induces a dipole in the other molecule and the dipoles interact, giving bonding. The surface of solid polymers consists of a homologous mixture of dispersion and polar components in differing amounts for the various polymers. For example, polyethylene and PP surfaces have no polar component, only dispersion bonding. 

Chemical bonding, Van der Waals The chemical bond that results from the dipole interaction between two atoms or non-polar molecules. Also called Dispersion bonding. 

Much of chemistry is concerned with the short-range wave-mechanical force responsible for the chemical bond. Our emphasis here is on the less chemically specific attractions, often called van der Waals forces, that cause condensation of a vapor to a liquid. An important component of such forces is the dispersion force, another wave-mechanical force acting between both polar and nonpolar materials. Recent developments in this area include the ability to measure... 

DFT calculations offer a good compromise between speed and accuracy. They are well suited for problem molecules such as transition metal complexes. This feature has revolutionized computational inorganic chemistry. DFT often underestimates activation energies and many functionals reproduce hydrogen bonds poorly. Weak van der Waals interactions (dispersion) are not reproduced by DFT a weakness that is shared with current semi-empirical MO techniques. 

The exchange repulsion and dispersive attraction com bine in what is referred to as a van der Waals term. Sometimes a potential is added to account for hydrogen bonding explicitly while in other situations this is expected to fall out of ordinary electrostatic interactions. 

Secondary Bonding. The atoms in a polymer molecule are held together by primary covalent bonds. Linear and branched chains are held together by secondary bonds hydrogen bonds, dipole interactions, and dispersion or van der Waal s forces. By copolymerization with minor amounts of acryhc (CH2=CHCOOH) or methacrylic acid followed by neutralization, ionic bonding can also be introduced between chains. Such polymers are known as ionomers (qv). 

Hydrophobic Interaction. This is the tendency of hydrophobic groups, especially alkyl chains such as those present in synthetic fibers, and disperse dyes to associate together and escape from the aqueous environment. Hydrophobic bonding is considered (7) to be a combination of van der Waals forces and hydrogen bonding taking place simultaneously rather than being a completely new type of bond or intermolecular force. 

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... 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

When thinking about chemical reactivity, chemists usually focus their attention on bonds, the covalent interactions between atoms within individual molecules. Also important, hotvever, particularly in large biomolecules like proteins and nucleic acids, are a variety of interactions between molecules that strongly affect molecular properties. Collectively called either intermolecular forces, van der Waals forces, or noncovalent interactions, they are of several different types dipole-dipole forces, dispersion forces, and hydrogen bonds. 

The aryl C—O—C linkage has a lower rotation barrier, lower excluded volume, and decreased van der Waals interaction forces compared to the C—C bond. Therefore, the backbone containing C—O—C linkage is highly flexible. In addition, the low barrier to rotation about the aromatic ether bond provides a mechanism for energy dispersion which is believed to be the principal reason for the toughness or impact resistance observed for these materials.15 17... 

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