Interfacial interaction force constants

With respect to nonionized organic solutes in aqueous solutions, the interfacial interaction force constants were expressed as constants that define the interfacial potential function as follows ... 

Both Equations 5.1 and 5.2 can be solved with appropriate boundary conditions and interfacial interaction force constants, generated from liquid chromatography experiments. 

One more factor, the contact, interaction, and transfer of chemical species on the hquid-frquid interface of two immiscible phases have to be mentioned in the general consideration of chemical kinetics. Little direct information is available on physicochemical properties (interfacial tension, dielectric constant, viscosity, density, charge distribution, etc.) of the interface. The physical depth of the interfacial region can be estimated in the distance in which molecular and ionic forces have their influence. On the aqueous side (monolayers of charged or polar groups) this is several nanometers, on the organic side is the influence of Van der Waals forces. These interfacial zone interactions may slower exchange and complex formation... 

The ratio (p/G) has the units of time and is known as the elastic time constant, te, of the material. Little information exists in the published literature on the rheomechanical parameters, p, and G for biomaterials. An exception is red blood cells for which the shear modulus of elasticity and viscosity have been measured by using micro-pipette techniques 166,68,70,72]. The shear modulus of elasticity data is usually given in units of N m and is sometimes compared with the interfacial tension of liquids. However, these properties are not the same. Interfacial tension originates from an imbalance of surface forces whereas the shear modulus of elasticity is an interaction force closely related to the slope of the force-distance plot (Fig. 3). Typical reported values of the shear modulus of elasticity and viscosity of red blood cells are 6 x 10 N m and 10 Pa s respectively 1701. Red blood cells typically have a mean length scale of the order of 7 pm, thus G is of the order of 10 N m and the elastic time constant (p/G) is of the order of 10 s. 

Recall that we already derived a similar expression from the van der Waals theory under a number of restrictive simplifications, see (2.5.44 and 45]. There the geometric mean was related to the same mean of Hamaker constants. This equation can be tested experimentally for liquids like water, in which a variety of forces are operative, y can be established by measuring interfacial tensions against organic liquids in which the interaction is dominated by the dispersion forces. This analysis can be illustrated with the data of table 2.3. In (2.11.19] a is an organic liquid (like a hydrocarbon, he) for which it was assumed that only dispersion forces determined the surface tension y = Consequently, y" is the only unknown. Its value appears to be invariant at about 22 mJ m", comprising 30% of the total tension. 

Case 2 Mn > M. Once the molecular weight exceeds a threshold value, M [24], PF2/6 forms hexagonal unit cells [51]. In this case the structure displays secondary effects due to the thin film geometry and the presence of interfacial forces. Here, there is a pronounced equatorial anisotropy with a measurable contraction of the lattice constants in the out-of-plane direction [52], These surface interactions also give rise to a distinctive biaxial... 

The rupture mechanisms of thin liquid films were considered by de Vries [15] and by Vrij and Overbeek [16]. It was assumed that thermal and mechanical disturbances (having a wavelike nature) cause film thickness fluctuations (in thin films), leading to the rupture or coalescence of bubbles at a critical thickness. Vrij and Overbeek [16] carried out a theoretical analysis of the hydrodynamic interfacial force balance, and expressed the critical thickness of rupture in terms of the attractive van der Waals interaction (characterised by the Hamaker constant A), the surface or interfacial tension y, and the disjoining pressure. The critical wavelength, for the perturbation to grow (assuming that the disjoining pressure just exceeds the... 

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