Surface Tension of Methanol

Figure A1.6. Surface tension of methanol. Linear region. Drawn line, values recommended by Jasper other references included for the sake of comparison.

Similar variations in the densities and surface tensions of mixtures are also known. The density of a mixture of bromo- and chlorobenzene is equal to the arithmetic mean of the densities of the individual components, whereas the density of trichloromethane-diethyl ether is about 1.5% above the mean value. The surface tensions of the systems diethyl ether-benzene and benzene-carbon disulfide are equal to the calculated values. The surface tension of methanol-ethyl iodide is greater and that of benzene-ethanol and acetone-carbon disulfide are less than the calculated values. 

Example 43 Estimate Surface Tension of a Water-Methanol... 

The elution of [60]- and [70]fullerenes was measured in water-methanol as a function of temperature on a poly(octadecylsiloxane) phase.67 The retention was shown to be dependent on the surface tension of the stationary phase through a simple geometrical model in which the solute formed a cavity in the stationary phase. In affinity chromatography, it was demonstrated that low ligand density may be a requirement for specificity of binding.68... 

Estimate the surface tension of pure methanol at 20°C, density 791.7 kg/m3, molecular weight 32.04. 

The units of interfacial tension are identical for surface tension, i.e., dyn/cm. Interfacial tension values of organic compoimds range from zero for completely miscible liquids (e.g., acetone, methanol, ethanol) up to the surface tension of water at 25 °C which is 72 dyn/cm (Lyman et al., 1982). Interfacial tension values may be affected by pH, surface-active agents, and dissolved gases (Schowalter, 1979). Most of the interfacial tension values reported in this book were obtained from Dean (1987), Demond and Lindner (1993), CHRIS (1984), and references cited therein. 

Mobile phases used in reversed-phase chromatography are frequently composed of mixtures of methanol and water or acetonitrile and water. Increasing the proportion of water causes an increased retention of the more hydrophobic solutes relative to the more polar solutes. The surface tension of the mobile phase plays a major role in governing solute retention, so an increase in temperature, by reducing viscosity, increases column efficiency and shortens retention times. 

Figure 3.3 Surface tension of a water droplet. A water droplet is shown on the left. A methanol droplet of the same volume is shown on the right. Water is capable of forming a much more extensive hydrogen-bond network than methanol, giving it much greater cohesive forces and allowing it to defy the force of gravity.

The composition dependence of the surface tension of binary mixtures of severed compounds with water is given in this table. The data are tabulated as a function of the mass percent of the non-aqueous component. Data for methanol, ethanol, 1-propanol, and 2-propanol are taken from Reference 1, which also gives values at other temperatures. 

The difference in pore shape was explained by the difference of interfacial tension between the polymer solutirm and the solvent or water droplet. Indeed, spreading water droplets over a unit area of a polymer solution can be determined by the spreading coefficient (5) as follows 5 = yp (yw + Xw/pl where yp is the surface tension of the polymer solution, y is the surface tension of the water droplet, and yw/p is the interfacial tension between the polymer solution and the water droplets in this case [90]. Water has the largest surface tension compared with the two alcohols, thus the water droplet spreading is reduced and water droplets maintain their spherical shape [89]. On the other hand, the value of yw/p is assumed to be very low for alcohol droplets because both methanol and ethanol are miscible with carbon disulfide. It should be noticed that under such alcoholic vapors, the polymer concentration should be higher than under aqueous atmosphere as no regular patterns were formed for polymer concentrations less than 10 g L. ... 

---