Concentric cylinders surface tension

For the experiment, the dorsal skin of young rats (Wistar or a comparable strain) is shaved and washed with an antibiotic solution (containing, e.g., streptomycin, penicillin, chloramphenicol, and amphotericin in concentrations inhibiting bacterial growth). After skin excision, excess fat is peeled off and the skin is placed over the end of a polytetrafluoroethylene tube with the epidermal side in touch with the hollow cylinder. The skin is fixed with an O-ring and the tube interior is sealed. The side of the dermis is then submersed in a magnesium sulphate solution (154 mM). The samples are applied at 30°C to the epidermal side of the skin in such a way that the skin interface is fully covered. After the incubation time, the substances are removed with prewarmed water the skin surface tension is decreased with ethanol which is subsequently replaced with magnesium sulphate solution (154 mM). 

One characteristic property of surfactants is that they spontaneously aggregate in water and form well-defined structures such as spherical micelles, cylinders, bilayers, etc. (review Ref. [524]). These structures are sometimes called association colloids. The simplest and best understood of these is the micelle. To illustrate this we take one example, sodium dode-cylsulfate (SDS), and see what happens when more and more SDS is added to water. At low concentration the anionic dodecylsulfate molecules are dissolved as individual ions. Due to their hydrocarbon chains they tend to adsorb at the air-water interface, with their hydrocarbon chains oriented towards the vapor phase. The surface tension decreases strongly with increasing concentration (Fig. 3.7). At a certain concentration, the critical micelle concentration or... 

Those who have studied the stability of masses of foam on solutions of surface-active substances find rather different results according to whether evaporation can, or cannot, take place. Bartsch3 examined the durability of foams on an extensive range of solutions, in closed cylinders, where the air space was saturated with water vapour the maximum of stability occurred at concentrations where there was some depression of surface tension, but far below those at which the maximum depression of tension was obtained. With moderately surface-active substances such as amyl alcohol, the maximum stability of the foams occurred at a reduction of tension roughly 12 dynes per cm. naturally the bulk concentration required to reach this varied with the length of hydrocarbon chain in the compound, but it was always only a small fraction of saturation. The stability of the foams rose very rapidly, as the bulk concentration increased from zero up to that at which the maximum fall of tension was obtained ... 

Variations to improve accuracy, facilitate handling, or render the method applicable to special systems have been proposed. For instance, Richards and Carver ) developed a capillary with a reflush device (a wider tube, parallel to the vertical capillary) to facilitate rejuvenation of the liquid surface. This apparatus was modified by Young and Gross ). Ramakrishnan and Hartland ) developed a procedure of measuring surface tensions in the annular ring between two concentric cylinders. This approach was duplicated by Agrawal and Menon ). Long ago Sentis ) experimented with an isolated capillary on the lower end of which a... 

Amphiphiles, the representatives of which are soap, surfactant and lipid, have a hydrophilic polar head and lipophilic nonpolar tails. They always remain on the interface between water and oil and form monolayers of surfactants in a water/oil/amphiphile ternary system. This monolayers or interfacial film reduce the surface tension between water and oil domains. In a three-component system the surfactant film exists in various topologically different structures such as micelles, vesicles, bicontinuous microemulsions, hexagonal arrays of cylinders or lamellar structures depending upon the pressure, temperature and the concentration of the components [1,2]. Microemulsions are thermodynamically stable, isotropic and transparent mixtures of ternary amphiphilic systems. When almost equal volume fractions of water and oil are mixed with a dilute concentration of surfactants, they take... 

A simple analysis of this problem follows from the condition that the contact zone can be arranged to be small compared with the radius of the monofilament. To calculate the deformations in the diametral plane, it is then adequate to consider the problem as the compression of a cylinder under concentrated loads (Figure 8.11(b)). For an isotropic cylinder, this is a well-known problem to be found in textbooks on elasticity (see Reference 20, p. 122). It is necessary to satisfy the boundary conditions on the surface of the cylinder, and this is done by addition of an isotropic tension in the plane perpendicular to the fibre axis. 

The rheology of highly concentrated emulsions was studied from a theoretical and experimental point of view by Princen and co-workers in the 1980s. They showed theoretically, for ordered structures, that the shear modulus of a concentrated system should depend directly on the interfacial tension and inversely on the radius (directly on the total surface area). In their bidimensional array of cylinders they obtained a volume fraction that was not directly extrapolable to truly tridimensional systems. This is due to the increase in interfacial area produced by the shear. Their model of deformation is shown in Figure 11.5. 

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