Interaction dispersive-type

The 12 RP fragments cap alternately the Cu4 faces of the Cu24 polyhedron, resulting in fivefold-coordinated phosphorus atoms. This structure resembles that of the recently described [Cu24(NPh)i4]4 anionic cluster (40). The Cu-P and Si-P distances are unremarkable. The construction principle of parallel Cu layers to form a metal-like package has also been observed for other Cu clusters (41). The main reason for the different structures of Cu2PR and Li2PR clusters is the covalent character of the Cu-P bond, with the additional involvement of favorable Cu-Cu interactions. The latter are probably due to relativistic d10-d10 interactions (dispersion-type of interaction) (42, 43). 

A monolayer can be regarded as a special case in which the potential is a square well however, the potential well may take other forms. Of particular interest now is the case of multilayer adsorption, and a reasonable assumption is that the principal interaction between the solid and the adsorbate is of the dispersion type, so that for a plane solid surface the potential should decrease with the inverse cube of the distance (see Section VI-3A). To avoid having an infinite potential at the surface, the potential function may be written... 

Dispersive Interactions. For pairs of nonpolar polymers, the intermolecular forces are primarily of the dispersive type, and in such cases the energy of interaction between unlike segments is expected to be closely approximated by the geometric mean of the energies of interaction between the two like pairs (98). In this case, the Flory-Huggins interaction energy between this polymer pair can be expressed in terms of the solubiUty parameters 5 of the pure components. 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

The most popular bonded phases are, without doubt, the reverse phases which consist solely of aliphatic hydrocarbon chains bonded to the silica. Reverse phases interact dispersively with solvent and solute molecules and, as a consequence, are employed with very polar solvents or aqueous solvent mixtures such as methanol/water and acetonitrile/water mixtures. The most commonly used reverse phase appears to be the brush type phase with aliphatic chains having four, eight or eighteen carbon atom chains attached. These types of reverse phase have been termed C4, C8 and Cl8 phases respectively. The C8... 

The pore structure of most cross-linked polystyrene resins are the so called macro-reticular type which can be produced with almost any desired pore size, ranging from 20A to 5,000A. They exhibit strong dispersive type interaction with solvents and solutes with some polarizability arising from the aromatic nuclei in the polymer. Consequently the untreated resin is finding use as an alternative to the C8 and Cl8 reverse phase columns based on silica. Their use for the separation of peptide and proteins at both high and low pH is well established. 

Interactive LC systems are those where solute retention is predominantly controlled by the relative strengths of the molecular interactions between solute molecules with those of the two phases. In such systems, exclusion and entropically driven interactions will be minor contributions to retention. The three basically different types of molecular interaction, dispersive, polar and ionic give rise to three subgroups, each subgroup representing a separation where one specific type of interaction dominates in the stationary phase and thus governs solute retention. The subgroups are as follows ... 

The CFC is initially a liquid because of intermolecular interactions (of the London dispersion type). Imagine that the interactions involves 4 kJ of energy but cooling the cheese to 5 °C we liberate about 6 kJ of energy it should be clear that more energy is liberated than is needed to overcome the induced dipoles. We say that... 

There are three basic types of contributions to the adsorbate-adsorbent interactions dispersion, electrostatic, and chemical bond. The latter, chemical bond, has been explored for adsorption only recently. Weak chemical bonds, particularly the broad type of bonds involving n electrons, or 7r-complexation, offer promising possibilities for designing new and highly selective sorbents. The subject of Tr-complexation sorbents will be discussed in a separate section. For physical adsorption, the adsorbate-adsorbent potential is... 

The studies discussed expand the use of the method for assessment of foetal lung maturity with the aid of microscopic foam bilayers [20]. It is important to make a clear distinction between this method [20] and the foam test [5]. The disperse system foam is not a mere sum of single foam films. Up to this point in the book, it has been repeatedly shown that the different types of foam films (common thin, common black and bilayer films) play a role in the formation and stability of foams (see Chapter 7). The difference between thin and bilayer foam films [19,48] results from the transition from long- to short-range molecular interactions. The type of the foam film depends considerably also on the capillary pressure of the liquid phase of the foam. That is why the stability of a foam consisting of thin films, and a foam consisting of foam bilayers (NBF) is different and the physical parameters related to this stability are also different. Furthermore, if the structural properties (e.g. drainage, polydispersity) of the disperse system foam are accounted for it becomes clear that the foam and foam film are different physical objects and their stability is described by different physical parameters. 

In the work of Famini and Wilson,a molecular volume, Vmc, (units of 100 A ) is used to model the cavity term that measures the energy required to create a solute-molecule sized cavity in the solvent. The dipolarity/polarizability term, which attempts to account for dispersion-type interactions, is modeled by the polarizability index, tij, (unitless). This index is defined as the average molecular polarizability divided by the molecular volume, a/Vmc, and helps account for the correlation between polarizability and molecular volume. 

Here, a is the polarizability related through TLSER descriptors by a = 7t 12 Vnic- The physical meaning of Eq. [31] is indicated by the negative sign on the polarizability term. Increased polarizability would increase the dispersion type intermolecular interactions and, thus, decrease the vapor pressure. 

The STM observation of the Y Cs2 dimers and clusters is direct experimental evidence that Y Cs2 molecules exhibit the superatom feature. The observed interfullerene distance is 11.2 A, which is shorter than that of the simple Y C82-Y Cs2 van der Waals distance (11.4 A), suggesting that the interfullerene interaction is not a simple dispersion type of weak interaction but a relatively strong interaction. A large dipole moment of Y Cs2 also plays an important role in the tight binding between Y Cs2... 

The nature of the analyte interactions with liophilic ions could be electrostatic attraction, ion association, or dispersive-type interactions. Most probably all mentioned types are present. Ion association is essentially the same as an ion-pairing used in a general form of time-dependent interionic formation with the average lifetime on the level of 10 sec in water-organic solution with dielectric constant between 30 and 40. With increase of the water content in the mobile phase, the dielectric constant increases and approaches 80 (water) this decrease the lifetime of ion-associated complexes to approximately 10 sec, which is still about four orders of magnitude longer than average molecular vibration time. 

In the contrast to the irreversible adsorption of amphiphilic ions on the reversed-phase surface, the liophiUc ions shows relatively weak interactions with the alkyl chains of the bonded phase. Liophilic means oil-loving. These liophilic ions are usually small inorganic ions and they possess an important ability for dispersive type interactions. They are (a) characterized by significant delocalization of the charge, (b) primarily symmetrical, (c) usually spherical in shape, and (d) absence in surfactant properties. 

A variety of parameters used to describe the polar interactions, dispersive forces and hydrogen bonding of molecules have been introduced. All of these parameters represent forces of attraction and were originally derived for low molecular weight compounds. Because the interactions between two molecules can be the result of a combination of all or any of these three force types, it is most convenient to select one parameter or a set of related parameters capable of dealing with all three forces. The Hansen cohesive energy parameter or solubility parameter, 6, with... 

For both conformations, terms of type 1 give half of the total second-order correction at least, but their variation from one form to the other is completely balanced by the variation of the terms of type 2 and 3. Dispersion terms of t5 e 5 (t e 4 is negligible) decrease the barrier slightly however, their effect is very small (0.2 kcal/mol) because of the large distance between the CH3 groups and of the high symmetry of the molecule. For instance, in a rotation of 60°, the dispersion type interaction between two CH bonds varies by an amount equal to 0.3 kcal/mol. 

---