Molecular cohesion pressure

The internal pressure is a differential quantity that measures some of the forces of interaction between solvent molecules. A related quantity, the cohesive energy density (ced), defined by Eq. (8-35), is an integral quantity that measures the total molecular cohesion per unit volume. - p... 

The cohesive pressure c is a measure of the total molecular cohesion per unit volume, given by eqn. 3.11... 

Cohesion Pressure. A term in Van der Waal s equation introduced to take care of the effect of molecular attraction. It is usually expressed as a/Vwhere at is a constant and V is the volume of the gas. 

Values of c are calculated from experimentally determined enthalpies (heats) of vapourization of the solvent to a gas of zero pressure, AH, at a temperature T, as well as from the molecular mass M, the density of the solvent g, and the gas constant, R. The cohesive pressure characterizes the amount of energy needed to separate molecules of a Hquid and is therefore a measure of the attractive forces between solvent molecules. The cohesive pressure c is related to the internal pressure n, because cohesion is related to the pressure within a liquid cf. Eq. (3-6) in Section 3.2 for the precise definition of n. ... 

An important measure of the total molecular cohesion per unit volume of liquid is the cohesive pressure c (also called cohesive energy density), which characterizes the energy associated with all the intermolecular solvent/solvent interactions in a mole of the solvent. The cohesive pressure is defined as the molar energy of vapourization to a gas at zero pressure, Af/y, per molar volume of the solvent, V, according to Eqs. (3-5) and (5-76) in Sections 3.2 and 5.4.2, respectively [93, 94]. The cohesive pressure c is related to the internal pressure n cf. Eq. (3-6) and Table 3-2 in Section 3.2. 

The viscosity of a iiquid has been reported to affect the onset of acoustic cavitation. Viscosity is a quaiitative measure of molecular interaction in a liquid. The higher the viscosity is, the higher are the attractive forces between the molecules and hence, the higher is the threshold intensity of US where cavitation starts. Based on experimental evidence, Briggs et al. [58] developed a quantitative relation between liquid viscosity q and the experimental value of the cohesive pressure Pco. which is defined as the difference between the hydrostatic pressure Po — which coincides with ambient pressure when no... 

Period II lasted 7 years oil yield was 4,500,000 tons and the amount of formation water produced was 2,900,000 tons. Formation pressure declined from 40 kg/cm to 15 kg/cm. Characteristically for this period, the water in the liquids recovered increased, then, towards the end of the period, decreased again. Gas dissolved in the oil provided the basic drive during this period. Forces of molecular cohesion between the oil and the reservoir rocks are weakened and oil mobility enhanced when water cut stays within the 35-50% range. 

The short-range repulsive interaction effect was taken into account by van der Waals by the first of the assumptions above. This assumption implies that the gas particles do not have the entire volume of a container available for motion. The volume needed to be reduced by a contribution determined by the volume from which the particles exclude each other. This volume unavailable for molecular motion is called the co-volume (van der Waals volume) of a gas. The assumed attraction in point 2 leads to the gas particles moving more closely together, just as if there was additional pressure upon them. This pressure or pull (or tensile stress ) caused by the forces of attraction is called the internal pressure or cohesion pressure of a gas. Van der Waals assumed that the general gas law should continue to be valid, except for the following two changes, a lessening of volume by the... 

However, solvation is not the only mode of action taken by the solvent on chemical reactivity. Since chemical reactions typically are accompanied by changes in volume, even reactions with no alteration of charge distribution are sensitive to the solvent. The solvent dependence of a reaction where both reactants and products are neutral species ( neutral pathway) is often treated in terms of either of two solvent properties. The one is the cohesive energy density or cohesive pressure measuring the total molecular cohesion per unit volume,... 

Only a few contributions of Mendeleeff, apart from the periodic law, can be mentioned. In a study of the thermal expansion of liquids he proposed the empirical formula Di=Dq i -kt), where D = density, temperature. In a study of surface tension he concluded that at the temperature at which a liquid changes to vapour regardless of pressure and volume (which he called the absolute boiling-point ), the cohesion and heat of vaporisation become zero , a recognition of the criticial point before Andrews (1863). Mendeleeff also recognised a relation between the molecular cohesion of a liquid and its chemical reactivity. The esterification of an alcohol by an acid occurs in such a way that the sum of the molecular cohesions of the products of the reaction (ester + water) is much greater than that of the reacting substances, an idea later applied to the influence of solvents. 

Here, terms (alV and b describe the deviations of gas from ideality. The value alV corresponds in its dimension to pressure it results from the molecules interaction and represents a so-called internal (cohesive) pressure p,. The term b takes into account the total volume of all gas molecules. Therefore (Y —b) is the volume free to molecular motion. Having removed the brackets the van der Waals equation can be rewritten as ... 

The fundamental principle of Hquid disiategration Hes ia the balance between dismptive and cohesive forces. The common dismptive forces ia atomizer systems iaclude kinetic energy, turbulent fluctuation, pressure fluctuation, iaterface shearing, friction, and gravity. The cohesive forces within the Hquid are molecular bonding, viscosity, and surface tension. 

Standard-grade PSAs are usually made from styrene-butadiene rubber (SBR), natural rubber, or blends thereof in solution. In addition to rubbers, polyacrylates, polymethylacrylates, polyfvinyl ethers), polychloroprene, and polyisobutenes are often components of the system ([198], pp. 25-39). These are often modified with phenolic resins, or resins based on rosin esters, coumarones, or hydrocarbons. Phenolic resins improve temperature resistance, solvent resistance, and cohesive strength of PSA ([196], pp. 276-278). Antioxidants and tackifiers are also essential components. Sometimes the tackifier will be a lower molecular weight component of the high polymer system. The phenolic resins may be standard resoles, alkyl phenolics, or terpene-phenolic systems ([198], pp. 25-39 and 80-81). Pressure-sensitive dispersions are normally comprised of special acrylic ester copolymers with resin modifiers. The high polymer base used determines adhesive and cohesive properties of the PSA. 

According to Eyring (Moore and Eyring, 1938) and Joly (1956), Newtonian flow in a monolayer is the result of a cohesive attraction between surfactant molecules. For every molecule that flows from higher to lower surface pressure in a motion parallel to the canal walls, there is another molecule ready to fill the hole vacated by the first. The mechanism for this cohesive flow is presumably attractive van der Waals interactions between hydrocarbon chains. This model assumes that the average intermolecular separation in a surface-continuous monolayer does not exceed the cross-sectional area of the molecule as defined by the average molecular area A of the film at the surface pressure n in the pressurized compartment of the viscometer. 

The molecular interaction is characterized by the specific cohesion or cohesion density UjV, where V is the molecular volume (Table 33). Another closely related quantity is the so-called internal pressure of a liquid. 

---