Interfacial tension response functions

Appendix 6A Application of System Theory for the Determination of Interfacial Tension Response Functions to Small Interfacial Area Disturbances... 

Appendix 6B Interfacial Tension Response Functions Ay(T) to Harmonic and Several Types of Transient Area Disturbances... 

By applying the inverse Fourier-Transform, according to the calculus discussed in (Miller et al., 1991), the interfacial tension response can be calculated. Under the assumption of a step-type disturbance the response function reads ... 

To calculate the interfacial tension response to any small area changes, the Fourier transform of the time function AlnA(t) has to be determined. For a periodic area change... 

The interfacial tension response of a system now results from the appropriate combination of an exchange function s(ico) with the actual area change fimction F(AlnA(t)) according to Eq. (6A.5). 

The interfacial tension response to transient and harmonic area perturbations yields the dilational rheological parameters of the interfacial layer dilational elasticity and exchange of matter function. The data interpretation with the diffusion-controlled adsorption mechanism based on various adsorption isotherms is demonstrated by a number of experiments, obtained for model surfactants and proteins and also technical surfactants. The application of the Fourier transformation is demonstrated for the analysis of harmonic area changes. The experiments shown are performed at the water/air and water/oil interface and underline the large capacity of the tensiometer. 

The goal of many experimental studies is to obtain the complex dilational viscoelasticity as a function of frequency (ico) from the measured interfacial tension response because this... 

Figure 8.12(b) shows the three-phase temperature intervals for Q2E4 and Q2E5 as a function of the number n of carbon atoms of n-alkanes. Figure 8.12(a) shows the detergency of these surfactants for hexadecane. Both parts of Fig. 8.12 indicate that the maximum oil removal is in the three-phase interval of the oil used (n-hexadecane) [78]. This means that not only the solubilisation capacity of the concentrated surfactant phase, but probably also the minimum interfacial tension existing in the range of the three-phase body are responsible for the maximum oil removal. Further details about the influence of the polarity of the oil, the type of surfactant and the addition of salt are summarised in the review of Miller and Raney [79]. 

THE VELOCITY FIELD. When a stream of fluid is flowing in bulk past a solid wall, the fluid adheres to the solid at the actual interface between solid and fluid. The adhesion is a result of the force fields at the boundary, which are also responsible for the interfacial tension between solid and fluid. If, therefore, the wall is at rest in the reference frame chosen for the solid-fluid system, the velocity of the fluid at the interface is zero. Since at distances away from the solid the velocity is finite, there must be variations in velocity from point to point in the flowing stream. Therefore, the velocity at any point is a function of the space coordinates of that point, and a velocity field exists in the space occupied by the fluid. The velocity at a given location may also vary with time. When the velocity at each location is constant, the field is invariant with time and the flow is said to be steady. 

The interface is described as before, using the approximation of smooth corrugations. The two electrolyte solutions are characterized by the solvent dielectric constants, e and si, and Debye lengths, k and In addition to the interfacial tension term, the free-energy functional now has two new terms. These are the electrostatic energy, Fg, and the term responsible for the entropy of a dilute electrolyte, Fg, so that... 

The capacitance of the water-ionic liquid interface was recently studied by Ishimatsu et al. [89] who measured electrocapillary curves and showed that the aqueous ions Li+ and CE are not specifically adsorbed on the aqueous side of the interface. More recently, Yasui et al. [90] have shown ultraslow responses, on the order of minutes, for the variation of the interfacial tension as a function of... 

Evolution of the RIT ratio as a function of time was obtained for a 70/30 PDMS/PIB blend containing different amounts of silica at 20 °C. Silica is an Aerosil Rhodorsil R972, R is the volume average diameter of the PIB droplets, is the apparent interfacial tension of the system [89]. To conclude, it seems that the displacement of the nanoparticles in the melted polymer blends and their localization in the final binary blend influences the compatibilization effect especially because it influences the origin of the droplet size reduction. On the other hand, the understanding of the mechanisms responsible... 

Surfactant is a lipid-protein complex that is synthesized and released hy alveolar type II epithelial cells. This complex surface-active compound contains both hydrophobic and hydrophilic regions to allow the molecule to spontaneously adsorb to and form monolayers along the air-liquid interface. The role of surfactant in pulmonary fluid mechanics depends on its natural ability to disrupt intermolecular forces by interfering with the attractive forces between water molecules at the interfacial surface—thus lowering the surface tension. While this surfactant mixture is largely comprised of lipids (90%), the surfactant proteins (10%) are required for normal function (Hall et al. 1992 Yu and Possmayer 1993). Finally, the molecule dipalmitoyl phosphatidylcholine (DPPC) makes up 80% of the phospholipid and is largely responsible for the ultra-low surface tensions necessary for respiratory function (<5 dyn/cm) (Klaus et al. 1961 Hawco et al. 1981 Tchoreloff et al. 1991). 

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