Water-hexadecane interfacial tension, effect

Figure 13.10 shows the effect of safflower oil concentration in hexadecane on the interfacial tension between water and hexadecane. As can be seen in fig. 13.10, the concentration-interfacial-tension profile shows the familiar features exhibited due to the adsorption of the amphiphilic vegetable oils. The entire concentration-interfacial-tension profile can be divided into three regions, depending on the concentration of safflower oil in hexadecane. These are (a) zero concentration of safflower oil in hexadecane characterized by very high water-hexadecane interfacial tension (b) intermediate concentration of safflower oil in hexadecane, up to about 0.05M, characterized by a rapid decrease in water-hexadecane interfacial tension and (c) very high concentration of safflower oil in hexadecane, >0.1M, characterized by water-hexadecane interfacial tension that is constant and independent of safflower oil concentration in hexadecane. Similar profiles were observed for other amphiphiles dissolved in hexadecane. The profile shown in fig. 13.10 is similar to that discussed before on the effect of vegetable oil concentration on boundary friction between metals (fig 13.5). 

FIGURE 13.10 Effect of safflower oil concentration in hexadecane on water-hexadecane interfacial tension. 

In a recent investigation, the effects of additives to the aqueous phase on the interfacial tension, y, vs. temperature curves near the freezing point of n-hexadecane were reported. The aim of these investigations was to determine the effect of additives such as proteins that are surface active on the snpercooled region and the interfacial tension. This would reveal the effect of the adsorbed protein molecule on the interfacial tension of the water-alkane system and could be used as a model for cell membranes. ... 

As mentioned previously, at the Y-shaped junction droplet formation takes place in a one-step mechanism that is determined by the viscous shear force and the interfacial tension force [11]. Because of this special feature, it was possible to directly measure the effect of interfacial tension on the droplet size using various systems with different static interfacial tensions. Water/ ethanol mixtures were used as continuous phase, and hexadecane and silicon oils as to-be-dispersed phase. The size of the droplets was recorded and a calibration curve constructed, and based on that curve, the dynamic interfacial tension could be estimated in systems that contain surfactants. 

Latex (emulsion) adhesives. In contact with water, adhesive bonds with latex adhesives may release surfactants, which will have the effect of lowering surface tension and changing the thermodynamic work of adhesion. Some latices based on copolymers of vinyl acetate were dried to give films which were then immersed in small quantities of water. The surface tensions (/w) fell from 72.8 mN m to values in the range 39-53 mN m in the first hour and then remained fairly static [76]. Measurements of interfacial tensions against n-hexadecane showed the dispersion components of surface tension remained essentially constant but polar components were reduced into the range 6-20 mN m ... 

Table 13.2 compares the free energies of adsorption of some vegetable oils obtained from Langmuir analysis of the adsorption isotherms. Data from steel-steel and starch-steel boundary-friction measurements, as well as from hexadecane-water interfacial-tension measurements, are compared. The data in table 13.2 show a number of interesting features on the effect of oil and substrate properties on AG ds. 

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