Surface tension, of liquids

Surface tension of liquids has been extensively analyzed in the literature. Some typical values of surface tension of different liquids are given in Table 2.1. A brief analysis of these data is given in the following text. 

Some comments are needed on these data in order to explain the differences in surface tension data and molecular structure. The range of y is found to vary from ca. 20 to over 1000 Nm/m. The surface tension of Hg is high because it is a liquid metal with a very high boiling point. This indicates that it needs much energy to break the bonds between Hg atoms to evaporate. Similarly, y of NaCl as a liquid (at high temperature) is also very high. The same case is found for metals in liquid state. 

The other liquids can be considered as under each type, which should help understand the relation between the structure of a molecule and its surface tension. 

Alkanes The magnitude increases by 1.52 mN/m per two CH2 when the alkyl chain length increases from 10 to 12 (n-Decane = 23.83 n-Dodecane = 25.35). 

Alcohols The magnitude of y changes by 23.7 - 22.1 = 1.6 mN/m per -CH2-group. This is based upon the y data of ethanol (22.1 mN/m) and propanol (23.7 mN/m). These observations indicate the molecular correlation between bulk forces and surface forces (surface tension y) for homologous series of substances. 

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The gradient model has been combined with two equations of state to successfully model the temperature dependence of the surface tension of polar and nonpolar fluids [54]. Widom and Tavan have modeled the surface tension of liquid He near the X transition with a modified van der Waals theory [55]. 

Because of the large surface tension of liquid mercury, extremely large supersaturation ratios are needed for nucleation to occur at a measurable rate. Calculate rc and ric at 400 K assuming that the critical supersaturation is x = 40,000. Take the surface tension of mercury to be 486.5 ergs/cm. ... 

D = diameter of droplet Dj = diameter of jet Pe = viscosity of liqi lid p = density of hquid <7 = surface tension of liquid... 

Surface tension of liquid Coalescence for removal Tabulated... 

Adhesion of particles Small particles experience adhesion forces, allowing them to attach to surfaces. These forces may be made up from surface tension of liquid films, or London (Van der Waals) forces. 

S" = clear height above foam or froth (equals tray spacing minus foam height above tray floor), ft p = viscosity of liquid, centipoise a = surface tension of liquid, dynes/cm We = entrainment (based on assumed allowance) lbs liquid/ (ft free plate area) (hr) hf = height of top of foam above tray floor, in. 

Pvm = Valve metal density, Ib/ft a = Surface tension of liquid, dy nes/cm... 

CT = surface tension of liquid, lb/ft = latent heat of vaporization, Btu/lb... 

For Yiv > YPv> where y v and Ypv are the surface tensions of liquid and protein, respectively, AFads increases with increasing ysv, predicting decreasing polymer adsorption. An example of this is phosphate buffer saline where y]v = 72.9 mJ/m2 and Ypv is usually between 65 and 70mJ/m2 for most proteins [5]. Therefore, supports for gel-permeation and affinity chromatography should be as hydrophilic as possible in order to minimize undesirable adsorption effects. 

TABLE III. SURFACE TENSIONS OF LIQUIDS USED FOR SOLID SURFACE CHARACTERIZATION... 

Quinn, E.L. (1927) The surface tension of liquid carbon dioxide. Journal of the American Chemical Society, 49 (11), 2704-2711. 

Periodic variations in the surface tension of liquid metals, c1 , are shown in Figure 6.5. The much higher surface tension of rf-block metals compared to the s- and p-block metals suggests that the surface tension relates to the strength of interatomic bonding. Similar periodic trends can be found also for the melting temperature and the enthalpy of vaporization, and the surface tension of liquid metals is strongly... 

Figure 6.7 Average grain boundary energy, y b, surface energy of crystals at 0 K, ysS, and surface tension of liquid Al, Ag, Au, Ni and Pt as a function of melting temperature 7W 2/3[8, 11],...

A, Mean free path of ions, meters Am Mean free path of electrons, ions, or molecules, meters a Surface tension of liquid or surface energy of solid, N/meter or J/ meter2... 

Qtc is zero because Qx 0. Thus, for zero flow rate, the equation reduces to the well-known Tate s law, which is used for finding the surface tension of liquids by the pendent drop or the forming bubble method. 

It is thus apparent from what has been discussed so far that the measurement of the surface tension of liquids is an important analysis. The method to use in the measurement of y depends on the system and experimental conditions (as well as the accuracy needed). For example, if the liquid is water (at room temperature), then the method used will be different from that if the system is molten metal (at very high temperature, ca. 500°C). These different systems will be explained in the methods described in this section. 

Effect of Temperature and Pressure on Surface Tension of Liquids... 

The role of surface tension of liquids is found in many important systems. The capillary vise is found to play an important role in many everyday processes (such as washing and cleaning, plants, etc.). 

FIGURE 5.2 The state of equilibrium between the surface tensions of liquid (GL)-solid (GS)-liquid/solid (GLS)-contact angle (CA). 

Since the surface tension of water is the same in the two systems, the difference in contact angle can only arise due to the surface tension of solids being different. The surface tension of liquids can be measured directly (as described in Chapter 2). However, this is not possible in the case of solid surfaces. Experiments show that, when a liquid drop is placed on a solid surface, the contact angle, 0, indicates that the molecules interact across the interface. This shows that these data can be used to estimate the surface tension of solids. 

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