Aqueous solutions surface tension

The difference between hydrophobicities of the hydroxyethyl (HE) grouping and the hydroxypropyl (HP) unit is evident in the relative aqueous solution surface tensions(7,8) of the two cellulosic polymers in these comparative references the M.S. of the products is not equal. The dramatic influence of the more hydrophobic HP groupings on surface pressures is illustrated in Figure 2. 

Table IX Aqueous-Solution Surface Tension (ff soin) of Fluorosilicone Surfactants...

Generalizations from the aqueous-solution surface tensions in Table IX are risky, because values are as dependent on the hydrophilic-lipophilic balance (HLB) as on the intrinsic surface activity of the hydrophobe. The data in Table IX are consistent with earlier observations that longer per-fluorinated groups are most effective in producing low surface tensions (in this case CF3(CF2)5-) and that a terminal CF2H- is detrimental. 

Attenuated total reflection infrared critical micelle concentration electron spectroscopy for chemical analysis hydrophilic-lipophilic balance poly(chlorotrifluoroethylene) poly(dimethylsiloxane) poly(tetrafluoroethylene) poly(trifluoropropylmethylsiloxane) glass transition temperature critical surface tension of wetting Owens-Wendt solid surface tension surface tension of aqueous solution surface tension of liquid... 

Riipinen I, Koponen IK, Frank GP, Hyvarinen AP, Vanhanen J, Lihavainen H, Lehtinen KEJ, Bilde M, Kulmala M (2007) Adipic and malonic acid aqueous solutions surface tensions and saturation vapor pressures. J Phys Chem A 111 12995-13002... 

With type 1 solutes, surface tension in aqueous solution mildly increases with concentration. Because activities generally increase with concentration, from Eq. (50), these solutes have a negative surface excess concentration (i.e., they are depleted in the surface layer). Inorganic electrolytes show this behavior. In the bulk solution, these ions are stabilized by interacting with the extended ionic environment of the solution. In the surface layer, this environment is limited in extent in one direction. 

Surfactant surface activity is most completely presented in the form of the Gibbs adsorption isotherm, the plot of solution surface tension versus the logarithm of surfactant concentration. For many pure surfactants, the critical micelle concentration (CMC) defines the limit above which surface tension does not change with concentration, because at this stage, the surface is saturated with surfactant molecules. The CMC is a measure of surfactant efficiency, and the surface tension at or above the CMC (the low-surface-tension plateau) is an index of surfactant effectiveness (Table XIII). A surfactant concentration of 1% was chosen where possible from these various dissimilar studies to ensure a surface tension value above the CMC. Surfactants with hydrophobes based on methylsiloxanes can achieve a low surface tension plateau for aqueous solutions of —21-22 mN/m. There is ample confirmation of this fact in the literature (86, 87). 

The prevalent explanation for isopropanol s role in this kind of dampening system is that its surface tension, about 29 dynes/cm, sufficiently lowers the aqueous fountain solution surface tension to allow wetting of the inked form-roller by that solution, as illustrated in Figure 1. That is, the fountain solution wets and spreads onto, and is carried by the ink film on the form-roller to the printing plate, as a relatively thin, uniform film. 

When the aqueous system contains finely divided solids, then foaming of the system may be influenced greatly by the nature of the dispersed solid particles. If the particles have a surface that is hydrophobic, and if the particles are divided finely enough, then the particles may adsorb onto the surface of any air bubbles introduced into the system and stabilize them against coalescence. They adsorb at the air-solid interface from the aqueous system because their solid-aqueous solution interfacial tension, ySL, is high and their solid/(nonpolar) air interfacial tension, ySA, is low because of their nonpolar surface. Consequently, their contact angle, 0, with the aqueous phase, from equation 6.3... 

Figure 14 shows the knee-shaped curve of solution surface tension vs. concentration characteristic of aqueous surface-active agents the steeper the curve, the more efficient the wetting agent. It is generally assumed that the bend of the curve coincides with the critical micelle concentration (c.m.c.) of the respective compound in the aqueous medium. Since the discontinuities in the slopes of the individual curves of Figure 14 occur in the region of the c.m.c. values reported by various... 

Adsorption is one of the most central topics in the science of coUoids and intafaces with appUcations in the stability of colloidal dispersions, cleaning, catalysis, surface modification and biotechnology. The Gibbs equation for the adsorption is the basic tool in the field and it can be, in principle, appUed to all interfaces. We can estimate the adsorption fi om surface tension-concentration data, thus Unking these important concepts. At low concentrations, e.g. dilute aqueous alcohol or surfactant solutions, surface tension... 

As an example of the application of the method, Neumann and Tanner [54] followed the variation with time of the surface tension of aqueous sodium dode-cyl sulfate solutions. Their results are shown in Fig. 11-15, and it is seen that a slow but considerable change occurred. 

We have considered the surface tension behavior of several types of systems, and now it is desirable to discuss in slightly more detail the very important case of aqueous mixtures. If the surface tensions of the separate pure liquids differ appreciably, as in the case of alcohol-water mixtures, then the addition of small amounts of the second component generally results in a marked decrease in surface tension from that of the pure water. The case of ethanol and water is shown in Fig. III-9c. As seen in Section III-5, this effect may be accounted for in terms of selective adsorption of the alcohol at the interface. Dilute aqueous solutions of organic substances can be treated with a semiempirical equation attributed to von Szyszkowski [89,90]... 

It is not uncommon for this situation to apply, that is, for a Gibbs mono-layer to be in only slow equilibrium with bulk liquid—see, for example. Figs. 11-15 and 11-21. This situation also holds, of course, for spread monolayers of insoluble substances, discussed in Chapter IV. The experimental procedure is illustrated in Fig. Ill-19, which shows that a portion of the surface is bounded by bars or floats, an opposing pair of which can be moved in and out in an oscillatory manner. The concomitant change in surface tension is followed by means of a Wilhelmy slide. Thus for dilute aqueous solutions of a methylcellu-... 

A 1.5% by weight aqueous surfactant solution has a surface tension of 53.8 dyn/cm (or mN/m) at 20°C. (a) Calculate a, the area of surface containing one molecule. State any assumptions that must be made to make the calculation from the preceding data, (b) The additional information is now supplied that a 1.7% solution has a surface tension of 53.6 dyn/cm. If the surface-adsorbed film obeys the equation of state ir(o - 00) = kT, calculate from the combined data a value of 00, the actual area of a molecule. 

The surface tension of an aqueous solution varies with the concentration of solute according to the equation y = 72 - 350C (provided that C is less than 0.05Af). Calculate the value of the constant k for the variation of surface excess of solute with concentration, where k is defined by the equation V = kC. The temperature is 25°C. 

In detergency, for separation of an oily soil O from a solid fabric S just to occur in an aqueous surfactant solution W, the desired condition is 730 = 7wo+7sw. Use simple empirical surface tension relationships to infer whether the above condition might be met if (a) 73 = 7w. (6) 70 = 7W, or (c) 73 = 70. 

The higher members of the series decrease the surface tension of aqueous solutions well below the point possible with any type of hydrocarbon surfactant, although in practice because of their strong acid character and solubiUty characteristics, more commonly salts and other derivatives are employed. A 0.1% solution of C F COOH has a surface tension of only 19 mN/m (dyn/cm) at 30°C (6). 

Surface Tension. The surface tension of aqueous solutions of PVA varies with concentration (Fig. 10), temperature, degree of hydrolysis, and acetate distribution on the PVA backbone. Random distribution of acetyl groups in the polymer results in solutions having higher surface tension compared to those of polymers in which blocks of acetyl groups are present (74—77). Surface tension decreases slightly as the molecular weight is reduced (Fig. 11). 

Fig. 10. Surface tension of aqueous poly(vinyl alcohol) solutions at 20°C and DP of 1700, where A represents 98—99 mol % hydrolyzed B, 87—89 mol %...

AH these mechanisms except high bulk viscosity require a stabilizer in the surface layers of foam films. Accordingly, most theories of antifoaming are based on the replacement or modification of these surface-active stabilizers. This requires defoamers to be yet more surface active most antifoam oils have surface tensions in the 20 to 30 mN/m range whereas most organic surfactant solutions and other aqueous foaming media have surface tensions between 30 and 50 mN/m(= dyn/cm). This is illustrated in Table 3. 

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