Surface tension Typical values

The surface tension of the coating is largely determined by the polymer and the solvent. The polymers usually have relatively high surface tensions, with values between 35 and 45 mN/m being typical. The organic... 

The widespread occurrence of the rectilinear relationship between cos0 and 7iv led Zisman to use the critical surface tension to characterize and compare the wettabilities of a variety of low-energy surfaces. Some typical values of yc for polymeric solids are shown in Table 2.3. The critical surface tension is an extremely useful parameter for the characterization of low-energy solids. Lee [43] has even derived an empirical relationship between jc and the glass transition temperature. However, Zisman has always emphasized that yc is not the surface free energy of the material, but only an empirical parameter the relative values of which act as one would expect the surface free energy to behave. Many subsequent authors have assumed that these two parameters are equal without comment. The relationships between yc, ysv and ys for a low-energy solid are discussed below. 

Figure 20 shows the plot of the surface tension vs. the logarithm of the concentration (or-lg c-isotherms) of sodium alkanesulfonates C,0-C15 at 45°C. In accordance with the general behavior of surfactants, the interfacial activity increases with growing chain length. The critical micelle concentration (cM) is shifted to lower concentration values. The typical surface tension at cM is between 38 and 33 mN/m. The ammonium alkanesulfonates show similar behavior, though their solubility is much better. The impact of the counterions is twofold First, a more polarizable counterion lowers the cM value (Fig. 21), while the aggregation number of the micelles rises. Second, polarizable and hydrophobic counterions, such as n-propyl- or isopropylammonium and n-butylammonium ions, enhance the interfacial activity as well (Fig. 22). Hydrophilic counterions such as 2-hydroxyethylammonium have the opposite effect. Table 14 summarizes some data for the dodecane 1-sulfonates.

Monoamidotriphosphate compounds have been evaluated for their combined detergent-sequestrant action [65,66]. Good surfactant properties are also attributed to organoaminodialkylenephosphonic acids. Typical compounds of this kind are the tetra- and trialkali salts of decyl-, dodecyl-, and tetradecylaminodi (methylphosphonate). Values of surface tension and detergency are given in Refs. 118 and 216-219. Wash test results, foam behavior, wetting performance, and surface tensions of aqueous solutions of phosphate esters have been tabulated [12,17,18,33,37,50,52,56,90,220]. 

When p approaches infinity, Equation 7 reveals that equals zero, which corresponds to infinitely fast sorption kinetics and to an equilibrium surfactant distribution. In this case Equation 6 becomes that of Bretherton for a constant-tension bubble. Equation 6 also reduces to Bretherton s case when a approaches zero. However, a - 0 means that the surface tension does not change its value with changes in surfactant adsorption, which is not highly likely. Typical values for a with aqueous surfactants near the critical micelle concentration are around unity (2JL) ... 

Fig. 4.7 Typical behavior of a solid detergent product during the first 20 minutes in a commercially available washing machine. Relevant parameters (pH value, conductivity A, surface tension y, peroxide content ) were detected by on-line sensorics.

In our case, nearly equal volume fractions of the two quark phases are likely to form alternating layers (slabs) of matter. The energy cost per unit volume to produce such layers scales as a2/3(r 2SC — niN )2/3 where a is the surface tension [25], Therefore, the quark mixed phase is a favorable phase of matter only if the surface tension is not too large. Our simple estimates show that max < 20 MeV/fm2. However, even for slightly larger values, 20 < a < 50 MeV/fm2, the mixed phase is still possible, but its first appearance would occur at larger densities, 3po < Pn < 5po. The value of the maximum surface tension obtained here is comparable to the estimate in the case of the hadronic-CFL mixed phase obtained in Ref. [26], The thickness of the layers scales as a1 /3(r/i2 SY -) — niN ) 2/3 [25], and its typical value is of order 10 fm in the quark mixed phase. This is similar to the estimates in various hadron-quark and hadron-hadron mixed phases [25, 26], While the actual value of the surface tension in quark matter is not known, in this study we assume that it is... 

Only surface energy is mentioned in the title of this review, but surface tension also is considered in the following text. The dimensions of (specific) surface energy (ergs/cm2 or joules/m2 or g/sec2) and of surface tension (dynes/cm or newtons/m or g/sec2) are identical. For typical liquids, also the two absolute values are equal for instance, the surface tension of water 7 at room temperature is about 72 dyne/cm, and the (specific) surface energy is 72 erg/cm2. 

To recapitulate the discrepancies in literature, Datta et al. (D4) varied the viscosity of water from 0.012 to 1.108 poise and found that with an increase in the viscosity, the bubble volume decreased for all the nozzles used. This is in apparent contradiction to the observations of most of the other investigators. An effort can now be made to explain this discrepancy on the basis of the present model. Note is to be made of the extremely small volumetric flow rates employed by Datta et al. (D4). In fact, they are in the range where effects due to viscosity are negligible when compared to the effects of surface tension. Thus, though there is a hundredfold increase in the viscosity, it is accompanied by a large variation in the surface tension, which decreases from 72.8 to 65.7 dyn per centimeter. At the very small flow rates employed, the decrease in the bubble volume observed by Datta et al. (D4) seems more likely to be due to this decrease in the surface tension rather than to the hundredfold increase in the viscosity. Thus, the influence of surface tension has been mistakenly attributed to the effect of viscosity. The actual values of the bubble volumes obtained by these authors for a typical nozzle are given in Table VI along with those obtained by the application of the present model. 

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. 

BLM surface tensions have been determined by the application of an ultrasmall hydrostatic pressure to one side of the membrane and measuring the resultant curvature changes by optical interferometry (Fig. 61). Typical values of 0.2-Q.3 mNm 1 were obtained for y for glyceryl monooleate and phosphatidyl-serine BLMs [413]. 

The changes in surface properties were analysed both by contact angles and gas permeabilities measurements. The contact angles values for a family of typical liquids are reported on Table 1. The resulting surface tensions, ys, for PE, EVOH and EVO-NO (34,... 

U2 and p-2 are the non-wetting phase velocity and dynamic viscosity respectively a is the surface tension and g is the gravitational acceleration. Similarly, the afore-mentioned non-dimensional parameters exhibit significantly low values in the GDL within comparable order of magnitude variations. It should be noted that for the hydrophobic CL and GDL representative of a typical PEFC, water is the non-wetting phase (NWP) and air the wetting phase (WP). 

Table 2.12 Typical Surface Tension Values of Selected Polymers at 180°C...

One special difficulty of applying parameterized models to chemical reactions deserves a special mention, namely that transition states often have charge distributions quite different from those against which solvation models are parameterized. For example, the partial atomic charge on Cl in the (Cl... CH3... Cl)-1 SN2 transition state is about -0.7, midway between the values (-1.0 and about -0.4, respectively) found in Cl-monatomic anion and typical alky chlorides. Thus the atomic radii and atomic surface tensions optimized against equilibrium free energies needs to be re-validated for transition structures. 

The molecular structure of retinoic acid is typical for an amphiphilic compound that is concentrated at interfaces. Further, the carboxylic acid groups allow such compounds to adjust their amphiphilic character by the degree of their dissociation. Surface tension measurements were carried out in order to determine the surface activity of retinoic acid [179]. The surface tension with respect to the concentration at pH 5 decreases more strongly than at pH 9. This reflects the fact that the protonated form of retinoic acid is more efficient in its surface activity than the deprotonated form. The critical micelle concentrations are 3.7 0.5 mg/L (pH 5) and 19 2 mg/L (pH 9). The limiting surface tension values in both curves is about 35 mN/m. Due to the precipitation of retinoic acid, the highest concentration in the surface tension curve at a pH of 5 was 20 mg/L. By contrast the solubility at pH 9 is at least 1 g/L. In order to verify the results from the FTIR measurements, films of the complexes were immersed in a solution of 0.15 mol/L sodium... 

Physical properties of the three test fuels are presented in Table I. Except for the surface tension of No. 6 fuel oil, which was a typical value, all properties were measured for the specific samples tested. The primary differences between the SRC-II middle distillate and the No. 2 fuel were the higher specific gravity, surface tension, and viscosity of the SRC-II. The No. 6 grade fuel, a residual fuel oil, had a much higher viscosity than either of the distillate fuels. Both the SRC-II and No. 2 fuel oil were sprayed at a nominal temperature of 80°F to simulate usage in a non-preheat combustion system. The No. 6 fuel oil was sprayed at temperatures ranging from 150° to 240°F in order to assess spray formation processes and spray quality over a broad range of viscosities. 

The specific values of exponents a, b, and c determined for the two distillate fuels are presented in Table II. The correlation of SMD with mass flow rate, pressure, and viscosity are in generally good agreement with typical values for petroleum fuels (11). Due to the limited properties variation available with these three fuels, the effects of surface tension and density could not be determined independently. 

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