Surface tension conversion factors

Wetting liquid Surface tension (dyn/cm) Conversion factor... 

Emulsion polymerization reactions are sometimes carried out with small seed particles formed in another reaction system. A number of advantages can he derived from using seed particles. In a batch reactor seed latex can he helpful hi controlling particle concentration, polymerization rate, particle morphology, and particle size characteristics. In a CSTR the use of a feed stream containing seed particles can also help to prevent conversion and/or surface tension oscillations, which are caused by particle formation phenomena, This factor will be discussed in more detail later in this chapter. 

Here, v is the surface tension per mole and A U the molar energy of vaporization. Conversion of y into y requires a model to establish the number of molecules contributing to y in the interface, a problem that is hidden in the oversimplified formula. Establishing a relation with the energy of vaporization is not, in itself, far-fetched, but the situation is more complicated and requires in the first place a proper distinction between y and U°. We already discussed this at the end of sec. 2.9, see fig. 2.16. Vavruch concluded that the factor should be lower than 0.5 moreover, it depends on the nature of the liquid and for some liquids, including water, it is strongly temperature-dependent. 

The size of micelles is determined by energetic factors and concentration factors. The decrease of CCMF in a viscous system must result in decrease of the size of the micelles. For increase of the surfactant concentration, the micelle size increases, and spherical micelles transform into elliptic ones and then into plate-shaped ones as increase in the surfactant concentration in common solvents is accompanied by a free energy advantage. It can be assumed that such a process occurs with the increase of the degree of conversion up to 30%. In this case CCMF shifts into the area of lower surfactant concentrations without any change in the surface tension (see Fig. 2.7). 

The second reason for the anomalous change of surface tension of a solid polymer containing surfactant lies in the structural and conformational conversions of the polymer itself under the influence of the surfactant. Such factors as the increase of the polymer surface tension when surfactant is added cannot be explained by the surfactant adsorption on the polymer surface only (see Fig. 2.13). Later we will consider this in detail. As was noted above, if the rate of aggregation of the surfactant molecules is higher than or equal to the rate of polymerization, the system surface tension alters during polymerization in the same way as in the coiu-se of the equilibrium process. At a high rate of polymerization, the formation of micelles of the maximum possible size can be hindered by the rapid increase of the system viscosity. In this case, when an IS substance is applied the split into two phases is not observed and the system appears to be more oversaturated by surfactant than in the first case. 

A and B indicate acid and base while E and C are susceptibilities to undergoing electrostatic and covalent interactions, respectively. The other parameters in Equation 15.9 are a conversion factor (/) and is the number of acid-base interaction sites on the surface. Drago et al (1965) have provided E and C values for about 30-40 acids and bases. In the case of benzene-water, the enthalpy of interaction is -5 kJ mol which incidentally is about Vi of heat of vaporization of benzene. This enthalpy of interaction corresponds to 16.5 mN m (assuming 50 as the area per molecule for benzene) and/= 1 both assumptions have been, however, criticized, see Douillard, 1997. Using such a value the improved Fowkes equation is, as shown by Fowkes et al. (1990), in excellent agreement with the experimental interfacial tension for water-benzene (35 mN m ) ... 

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