Interfacial tension origin

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. 

Interfacial driven disturbances on a Newtonian thread embedded in a Newtonian matrix are briefly discussed next. An initially long cylindrical thread with midsection radius Ro is sinusoidally disturbed by a wave of interfacial tension origin as shown in Figure 6.24a. Without going into the details of the analysis we note that the burst time (Elmendorp, 1991) is given as... 

The entropically driven disorder-order transition in hard-sphere fluids was originally discovered in computer simulations [58, 59]. The development of colloidal suspensions behaving as hard spheres (i.e., having negligible Hamaker constants, see Section VI-3) provided the means to experimentally verify the transition. Experimental data on the nucleation of hard-sphere colloidal crystals [60] allows one to extract the hard-sphere solid-liquid interfacial tension, 7 = 0.55 0.02k T/o, where a is the hard-sphere diameter [61]. This value agrees well with that found from density functional theory, 7 = 0.6 0.02k r/a 2 [21] (Section IX-2A). 

The Good-Girifalco theory [77-82] was originally formulated to make an attempt to correlate the solid-liquid interfacial tension to the solid surface energy and the liquid surface tension through an interaction parameter, basic formulation of the theory is ... 

Electroneutral substances that are less polar than the solvent and also those that exhibit a tendency to interact chemically with the electrode surface, e.g. substances containing sulphur (thiourea, etc.), are adsorbed on the electrode. During adsorption, solvent molecules in the compact layer are replaced by molecules of the adsorbed substance, called surface-active substance (surfactant).t The effect of adsorption on the individual electrocapillary terms can best be expressed in terms of the difference of these quantities for the original (base) electrolyte and for the same electrolyte in the presence of surfactants. Figure 4.7 schematically depicts this dependence for the interfacial tension, surface electrode charge and differential capacity and also the dependence of the surface excess on the potential. It can be seen that, at sufficiently positive or negative potentials, the surfactant is completely desorbed from the electrode. The strong electric field leads to replacement of the less polar particles of the surface-active substance by polar solvent molecules. The desorption potentials are characterized by sharp peaks on the differential capacity curves. 

Influenced by interfacial tension and centrifugal forces, spherical drops of various diameters originate at the holes. If we again assume the Sauter diameter, according to Eq. (9.1), as the mean diameter of the spectrum of particles, the following equation for heavy and light phases results from theoretical and experimental results [10] ... 

In the case of the interfacial tension of two pure liquids we have had to deal with the superficial system in equilibrium with a two phase two component system of three dimensions. If we add to this system a third component the problem becomes still more complicated. The simplest case is that in which the added substance is soluble in one phase and completely insoluble in the other, the original liquids being themselves mutually insoluble. The change of interfacial tension should then run parallel to the change of surface tension of the liquid in which the third component dissolves. 

If the original liquids are mutually soluble and the third component is soluble in only one of them, the mutual solubility will be diminished by its addition—according to Nernst s law, at low concentrations. The rise or fall of interfacial tension will thus depend on two superimposed effects, the change of surface tension of the better solvent owing to addition of the solute, and that in each of the two liquids due to diminished concentration of the other. The latter effect tends to increase the tension while the former may work in either direction. 

If the original liquids are again partially miscible, and the added component soluble in either the mutual solubility may be increased if so the interfacial tension will probably diminish whatever may be the effect on the surface tensions of the two pure liquids. Clearly, if sufficient of the third component be added to make the two phases completely soluble the interfacial tension must disappear altogether. 

The original eddy motion which sets up the chain of events leading to eruptions may be caused by forced flow of the bulk phases, density differences due to concentration or temperature gradients (B12), or earlier eruptions. Strong eruptions occur when a critical concentration driving force or a critical interfacial tension depression is exceeded (03, S8, S9). At lower concentration differences ripples may result (E4), eruptions may occur only over part of the interface (S8) with the jets taking some time to form (T9), or no interfacial motion at all may occur. Attempts to correlate the minimum driving force required for spontaneous interfacial motions have met with little success. 

Akovali and Ulkem [33] reported the surface modification of carbon black by plasma polymerization of styrene and butadiene. The effect of such plasma-coated carbon black was studied in a SBR matrix. A slight increase in the tensile strength was observed for the plasma-polymerized styrene-coated carbon black. This was explained by a decrease in the interfacial tension, as the result of the similarities between the treated filler and the matrix at the interface. They also concluded that the plasma coating obtained on carbon black is so thin that no blockage of the pores occurred and that there was no decrease in the original absorptive capacity. 

The theoretical foundation of the drop volume technique (DVT) was developed by Lohnstein (1908, 1913). Originally, this method was only intended to determine static interfacial tension values. Over the past 20 years, the technique has received increasing attention because of its extended ability to determine dynamic interfacial tension. DVT is suitable for both liquid/liquid and liquid/gas systems. Adsorption kinetics of surface-active substances at liquid/liquid or liquid/gas interfaces can be determined between 0.1 sec and several hours (see Fig. D3.6.5). 

The various regimes of low-viscosity liquid which can exist in an agglomerate are depicted in Fig. 2.3. For regular systems of spherical packing, the cohesive forces have been calculated [1,8—10]. These forces originate with the interfacial tension at the liquid surface and the pressure deficiency (suction) created within the liquid phase by curvature at the liquid surface. 

Suppose that water is not originally in contact with the solid surface and adheres to it (i.e., adhesional wetting). When the drop of water is laid on a flat, smooth, solid surface, three forces are at work surface tension between the solid and air, ySA interfacial tension between the solid and water, ysw and surface tension between water and air, yWA. Incorporating only the horizontal components of these forces leads to ... 

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