Hydrogen bonding interfacial tension

Using the Hansen method for the interfacial tension, the dispersion, polar and hydrogen bonding surface tensions of PS are estimated to equal 26.28, 4.65 and 2.067, respectively. All values in mN m The surface tension of forma-mide is equal to 58.2 mN m . ... 

It is estimated that about one third of the interfacial tension is due to Van der Waals attraction, and the remainder is due to hydrogen bonding. 

The hydrogen bonding between the head group of the surfactant and water is very sensitive to temperature for this reason d/u /dT is expected to be larger at low temperatures. Because the hydrophobicity of the surfactant increases with temperature, dC wl/dT < 0. In reality, the critical micelle concentration passes through a minimum with increasing temperature [20]. The minimum is, however, located around 55°C for nonionic surfactants. As a result, the interfacial tension is expected to pass through a minimum. 

At the liquid-liquid interface between a hydrocarbon oil and water under mixing, the molecules encounter unbalanced attraction forces, pull inwardly, and contract as other molecules leave the interface for the interior of the bulk liquid. As a result, spherical droplets are formed. Customarily, the boundaries between a liquid and gas and between two liquids are the surface and the interface, respectively. The interfacial tension (or interfacial free energy) is defined as the work required to increase the interfacial area of one liquid phase over the other liquid phase isothermally and reversibly. Moving molecules away from the bulk to the surface or interfacial surface requires work (i.e., an increase in free energy). Water molecules and hydrocarbon oil molecules at the interface are attracted to the bulk water phase as a result of water-water interaction forces (i.e., van der Waals dispersion y and hydrogen bonding y ), to the bulk oil phase due to the oil-oil dispersion forces, y 1, and to the oil-water phase by oil-water interactions, y )W (i.e., dispersion forces). As mentioned in Chapter 3, the oil-water dispersion interactions are related to the geometric mean of the water-water and oil-oil dispersion interactions. The interfacial tension is written as ... 

Table 4.3 shows the surface tensions and the interfacial tensions against water at 20°C. Based on the interfacial tension or surface tension measurement, it is possible to calculate the water-water dispersion and hydrogen bonding forces. The value of the surface tension is the sum of the combined dispersion and the hydrogen bonding forces. For example, for the water-n-octane system,... 

A similar imbalance of attractive forces exists at the interface between two immiscible liquids. Table 6.1 lists surface tensions of various liquids and also interfacial tensions at the liquid/water interface. The value of the interfacial tension is generally between those of the surface tensions of the two liquids involved, except where there is interaction between them. Table 6.1 includes several such examples. The interfacial tension at the octanol/water interface is considerably lower than the surface tension of octanol owing to hydrogen bonding between these two liquids. 

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