Surface tension temperature effect

Effect of Temperature on Surface Tension According to the kinetic theory, molecular kinetic energy is proportional to absolute temperature. The rise in temperature of a liquid, therefore, is accompanied by increase in energy of its molecules. Since intermolecular forces decrease with increase in the energy of molecules, the intermolecular forces of attraction decrease with rise of temperature. 

For both ionic and POE nonionics, as the temperature is increased, there is a decrease in both Ym and the CMC/C2o ratios. As a result, although the surface tension of the solution may be reduced to a lower value by increase in the temperature, the surface tension reduction effectiveness, IIcmc (= To — Ycmc> where y0 is the surface tension of the pure solvent at that temperature), is always reduced by increase in temperature. 

Mashayek and Ashgriz [98] considered effects of the heat transfer from the liquid to the surrounding ambient, the liquid thermal conductivity, and the temperature-dependent surface tension coefficient on the jet instability and the formation of satellite drops. Two different disturbances were imposed on the jet. In the first case, the jet is exposed to a spatially periodic ambient temperature. In addition to the thermal boundary condition, an initial surface disturbance with the same wave number as the thermal disturbance is also imposed on the jet. Both in-phase and out-of-phase thermal disturbances with respect to surface disturbances are considered. For the in-phase thermal disturbances, a parameter set is obtained at which capillary and thermocapiUary effects can cancel each other and the jet attains a stable configuration. No such parameter set can be obtained when the thermocapillary flows are in the same direction as the capillary flows, as in the out-of-phase thermal disturbances. In the second case, only an initial thermal disturbance is imposed on the surface of the liquid while the ambient temperature is kept spatially and temporally uniform (Fig. 1.20). 

Shulman and coworkers measured the surface tensions of malonic, glutaric, succinic, oxalic, adipic, phthalic, and c A-pinonic acids in water and 0.5-2 M (NH4)2S04 at room temperature [93]. Surface tension depression was visible with increasing organic concentration and carbon number for all species except for phthalic and oxalic acid, which had no surface tension effect. The concentration of salt used did not affect the surface tension of any organic material except for cis-pinonic acid, which showed increased surface tension depression as salt concentration increased, possibly due to salting out [187]. Vanhanen et al. studied succinic acid in NaCl solutions from 283 to 303 K, and found enhanced surface tension depression as soon as succinic acid was added [209]. 

At non-zero temperatures the surface tension can be calculated only in the mean-field approximation, after solving the integral equation for p(z). This has been done numerically for the penetrable-sphere model, and analytically for a penetrable-cube model, in which the spheres are replaced by oriented cubes of volume Uo. The effective density or(z) is then given by an equation simpler than (5.83), viz. 

Fig. 2.4 Effect of temperature on surface tension and dynamic viscosity of water, data from [14]...

The principal point of interest to be discussed in this section is the manner in which the surface tension of a binary system varies with composition. The effects of other variables such as pressure and temperature are similar to those for pure substances, and the more elaborate treatment for two-component systems is not considered here. Also, the case of immiscible liquids is taken up in Section IV-2. 

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

For many laboratoiy studies, a suitable reactor is a cell with independent agitation of each phase and an undisturbed interface of known area, like the item shown in Fig. 23-29d, Whether a rate process is controlled by a mass-transfer rate or a chemical reaction rate sometimes can be identified by simple parameters. When agitation is sufficient to produce a homogeneous dispersion and the rate varies with further increases of agitation, mass-transfer rates are likely to be significant. The effect of change in temperature is a major criterion-, a rise of 10°C (18°F) normally raises the rate of a chemical reaction by a factor of 2 to 3, but the mass-transfer rate by much less. There may be instances, however, where the combined effect on chemical equilibrium, diffusivity, viscosity, and surface tension also may give a comparable enhancement. 

Figure 1 determines the foregoing temperature effect and is easier to use than the equation or a nomograph proposed by Kharbanda for this relation. The results are fairly accurate, provided the temperatures for which the surface tensions are considered are not close to the critical temperature of the material in question. Best results are obtained for nonpolar compounds. 

Physical characteristics Molecular weight Vapour density Specific gravity Melting point Boiling point Solubility/miscibility with water Viscosity Particle size size distribution Eoaming/emulsification characteristics Critical temperature/pressure Expansion coefficient Surface tension Joule-Thompson effect Caking properties... 

Thus apolar probe liquids of sufficiently high surface tension to yield finite contact angles against many surfaces are especially valuable for this purpose. Popular examples of these include diiodomethane, with a surface tension of 50.8 mN/m at 23°C, and a-bromonaphthalene, with a surface tension of 44.4 mN/m at the same temperature. One should be cautioned, however, that both are sufficiently volatile that the 7re-effects may not be negligible with their use. 

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