Surface tension minimum value

Figure 1 Surface tension equilihrium values, Yeq (mN/m) of clinical samples from infants with NRDS 1. before Curosurf therapy, n=10 2 - after Curosurf therapy, n=12. 3 - Curosurf pure dispersion for control, n-number of clinical samples. Data are presented as mean values SD (minimum three different drops of each sample)...

We noted in Section VII-2B that, given the set of surface tension values for various crystal planes, the Wulff theorem allowed the construction of fhe equilibrium or minimum firee energy shape. This concept may be applied in reverse small crystals will gradually take on their equilibrium shape upon annealing near their melting point and likewise, small air pockets in a crystal will form equilibrium-shaped voids. The latter phenomenon offers the possible advantage that adventitious contamination of the solid-air interface is less likely. 

Since capillary tubing is involved in osmotic experiments, there are several points pertaining to this feature that should be noted. First, tubes that are carefully matched in diameter should be used so that no correction for surface tension effects need be considered. Next it should be appreciated that an equilibrium osmotic pressure can develop in a capillary tube with a minimum flow of solvent, and therefore the measured value of II applies to the solution as prepared. The pressure, of course, is independent of the cross-sectional area of the liquid column, but if too much solvent transfer were involved, then the effects of dilution would also have to be considered. Now let us examine the practical units that are used to express the concentration of solutions in these experiments. 

Measurement of the differential capacitance C = d /dE of the electrode/solution interface as a function of the electrode potential E results in a curve representing the influence of E on the value of C. The curves show an absolute minimum at E indicating a maximum in the effective thickness of the double layer as assumed in the simple model of a condenser [39Fru]. C is related to the electrocapillary curve and the surface tension according to C = d y/dE. Certain conditions have to be met in order to allow the measured capacity of the electrochemical double to be identified with the differential capacity (see [69Per]). In dilute electrolyte solutions this is generally the case. 

Tension in the free surface of a liquid is the cause of the tendency of a liquid surface to assume the form having a minimum area, as manifested in the shape of a bubble or a drop of liquid.25 The tendency to contract is a special case of the general principle that potential energy tends toward a minimum value. 

The potential of zero charge (pzc) is a characteristic potential for a given interface, and hence is of obvious interest. In the absence of specific adsorption, it can be measured as the potential at which the Gouy-Chapman capacity obtains its minimum this value must be independent of the electrolyte concentration, otherwise there is specific adsorption. For liquid metals the pzc coincides with the maximum of the surface tension (see Section 3.5). 

The influence of surface tension of the system and of the orifice radius were found to be small. Surface tension, however, has an effect on the minimum value of P for bubbling to occur, since bubbling ceases if P is less than 2 y/R. 

Values of the critical micelle concentration (cmc), minimum area per molecules " cnic effectiveness of surface tension reduc-... 

C gDAO with SDS respectively. For LDAO/SDS ratio greater than 1, these mixed solutions are turbid and blrefrlngent addition of SDS results in production of filament-like structures. When the molar amount of SDS is equal to or greater than that of the LDAO, the solutions become Isotropic and clear. AT 3 1 LDAO/SDS molar composition, the change in pH reaches its maximum value. Minimum surface tension is reached when the LDAO content is still in excess, unlike the cases of Cj 2 C] 4 DA0. This observation... 

For the higher homologs (i.e., 12 to 14 LAS), the values of Gguif more nearly, but not completely, constant. They vary first due to hardness. This reflects on the fact that Gg j f values of Yw 50 ppm are higher than at 150 and 300 ppm. At the higher hardnesses, the sulfonate group repulsion for the adsorbed LAS molecules is at a minimum in the presence of excess divalent cation (i.e., hardness). This results in better LAS packing in the interface, lower surface tensions, and lower CED values which finally culminates in a lower Gg xf should be... 

The higher the negative deviation from ideality in monolayer formation, the lower the concentration required to attain a given surface tension below the CMC. The higher this deviation for micelle formation, the lower the CMC. Since the CMC is where the surface tension approximately levels out at near a minimum value, the minimum surface tension in such a system represents the relative enhancement of monolayer formation over micelle formation. This relative favorability of aggregate formation is often an important factor in many applications, as will be further discussed in this article. 

The surface tension y of the aqueous solution of dodecylammonium chloride — decylammonium chloride mixture was measured as a function of m at a given value of the mole fraction X of DeAC at 298.15 K under atmospheric pressure. The results are shown in Figure 1. It is seen that the y vs. m curves are similar in appearance. This behavior is in harmony with that observed previously in a low concentration range (9). Moreover, the formation of micelle is found to cause the curves to break sharply at the CMC which increases with X. It should be noted, however, that the y vs. m curve of a mixture has a very shallow minimum in the immediate vicinity of the CMC. 

Octadecanol was recrystallized from hexane after fractionation by vacuum distillation, and its purity was checked by gas-liquid chromatography. Dodecylammonium chloride was recrystallized from a mixture of ethanol and water, and its purity was confirmed by the fact that it had no minimum near the critical micelle concentration on the surface tension vs concentration curve. Hexane was distilled after passing through an activated alumina column. Water was distilled from alkaline permanganate solution of distilled water after refluxing for one day. The purity of hexane and water was confirmed by the value of the interfacial tension between them. 

The relative mol. compressibility of ammonium bromide in 700 mols. of solvent is 0973, and in 1500 mols. of the solvent, 0951—vide ammonium iodide. W. C. Rontgen and J. Schneider 9 also measured the surface tension of these soln. The viscosity of ammonium bromide at 25° decreases from 0 008867 dynes per sq. cm. for 0 216A-soln. to O 008254 for 2 646Ar-soln., and then increases from this minimum to 0 008560 with 4 920A-soln. The respective sp. gr. of these soln. are T0121, 1 1414, and 12605. The values for l 63A-soln. decrease from 0 0116 at 10°, to 00077 at 30°, to 0 0056 at 50°. The velocity of diffusion of ammonium bromide in aq. soln. is smaller than that of potassium bromide, and greater than sodium bromide.10... 

The following two items need to be considered from a practical perspective, especially for ionic surfactants, when measuring the CMC of surfactants (Constantinides and Steim, 1985) (a) surface-active impurities in commercial surfactants, such as SDS, give rise to a minimum in the surface tension-concentration plot, and unless a highly puriLed surfactant is used an approximate value ol the CMC is obtained, and (b) in the dye solubilization method, it is important that the dye and the surfactant are of the same charge, to avoid premicellar association, that is, salt formation between the dye and the surfactant below the true CMC of the surfactant. 

Figure 2 presents surface tension and E values obtained for fermented broth at different initial pH values in CS media. For all the pH values tested, a decrease in surface tension of the medium was noted before inoculation (62.5 dyn/cm) by the microorganism activity. These results indicate that the tested bacteria have the ability to produce biosurfactant at pH values ranging from 5.0 to 8.0 The minimum surface tension values of 30.1 and 31.5 dyn/cm were obtained when the medium s initial pH was 7.0 and 8.0, respectively. 

The efficiency of surfactant adsorption is determined as a function of minimum bulk surfactant concentration, C that produces saturation adsorption (rmax) at the liquid-gas or liquid-liquid interface. This minimum concentration is defined as p C20 which is (— log C2o) reducing the surface or interfacial tension by 20 dyne cm-1 (n = 20 dyne cm-1). With Qo, r lies between 84 and 99.9% of rmax. The larger the pC2o (smaller the C), the more efficient the surfactant is in adsorbing at the interface and reducing the surface tension at liquid-gas or interfacial tension at liquid-liquid interfaces. The pC20 values for several surfactants can be found in Chapter 2 of [2]. 

From the experimental values of the zeta potentials for air bubbles [32], one could infer that the surface potential should be approximately 0.060 V for 0.001 M NaCl at pH 7. However, this value is much too large to be in agreement with the experiments of Jones and Ray [33]. The depletion thickness vanishes at the minimum of the surface tension, and at this surface potential, the adsorption thickness, due to the Poisson-Boltzmann effect, would be over 200 A and could not be compensated by the other interactions discussed here. The value which had to be selected for N... 

To estimate the influence of the surfactant adsorption on the capillary forces, the wetting tension yiv cos was calculated from the values given in Fig. 10a. The results drawn in Fig. 10b show for both measurement series a minimum of the capillary forces exactly at the concentration ceff. The capillary forces are reduced by about 20% compared to water. This confirms the hypothesis that the reduction of the pattern collapse is caused by a hydropho-bizing of photoresist processed with the threshold dose by cationic surfactant adsorption. Unfortunately the inverse ADS A method could not be applied at relative surfactant concentrations >0.2 since the bubbles became unstable due to the lower surface tension. Thus it cannot be estimated how the wetting tension evolves at higher concentrations. 

Simple sequential processes frequently do not yield particles with the planned architectures. This is because of the complexity of emulsion polymerizations and because a system in which different polymers coexist with water will tend to rearrange toward the composition with the lowest overall surface energy. Theoretical descriptions of such phenomena [17-19] are based on the concept that the final state of the system consisting of polymer I, polymer 2, and water (labeled phase 3) depends on the three interfacial tensions yi2, Y2i and y2.i. and the corresponding interfacial areas. The equilibrium state of the three phases is determined by the minimum value of the surface free energy, Gy. 

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