Surface tension data

Fig. Ill-IS. Surface tension data for aqueous alcohol illustration of the use of the Gibbs equation. (1) -butyl (2) -amyl (3) -hexyl (4) -heptyl (5) -octyl. (Data from Ref. 126).

McBain reports the following microtome data for a phenol solution. A solution of 5 g of phenol in 1000 g of water was skimmed the area skimmed was 310 cm and a 3.2-g sample was obtained. An interferometer measurement showed a difference of 1.2 divisions between the bulk and the scooped-up solution, where one division corresponded to 2.1 X 10 g phenol per gram of water concentration difference. Also, for 0.05, 0.127, and 0.268M solutions of phenol at 20°C, the respective surface tensions were 67.7, 60.1, and 51.6 dyn/cm. Calculate the surface excess Fj from (a) the microtome data, (b) for the same concentration but using the surface tension data, and (c) for a horizontally oriented monolayer of phenol (making a reasonable assumption as to its cross-sectional area). 

The molecules in a gas-hquid interface are in tension and tend to contract to a minimum surface area. This tension may be quantified by the surface tension, which is defined as the force in the plane of the surface per unit length. Jasper" has made a critical evaluation of experimental surface tension data for approximately 2200 pure chem-ic s. He correlates surface tension C (mN/m = dyn/cm) with temperature T (°C) over a specified temperature range as... 

Critical surface tension data for low-energy surfaces of varying surface chemistry obtained from Zisman plots... 

Kakiuchi and Senda [36] measured the electrocapillary curves of the ideally polarized water nitrobenzene interface by the drop time method using the electrolyte dropping electrode [37] at various concentrations of the aqueous (LiCl) and the organic solvent (tetrabutylammonium tetraphenylborate) electrolytes. An example of the electrocapillary curve for this system is shown in Fig. 2. The surface excess charge density Q, and the relative surface excess concentrations T " and rppg of the Li cation and the tetraphenylborate anion respectively, were evaluated from the surface tension data by using Eq. (21). The relative surface excess concentrations and of the d anion and the... 

Recently, Samec et al. [38] have investigated the same system by the video-image pendant drop method. Surface tension data from the two studies are compared in Fig. 2, where the potential scale from the study [36] was shifted so that the positions of the electrocapillary maxima coincide. The systematic difference in the surface tension data of ca. 3%, cf. the dotted line in Fig. 2, was ascribed to the inaccurate determination of the drop volume, which was calculated from the shape of the drop image and used further in the evaluation of the surface tension [38]. A point of interest is the inner-layer potential difference A (pj, which can be evaluated relative to the zero-charge potential difference A cpp c by using Eq. 

Girault and Schiffrin [6] and Samec et al. [39] used the pendant drop video-image method to measure the surface tension of the ideally polarized water-1,2-dichloroethane interface in the presence of KCl [6] or LiCl [39] in water and tetrabutylammonium tetraphenylborate in 1,2-dichloroethane. Electrocapillary curves of a shape resembling that for the water-nitrobenzene interface were obtained, but a detailed analysis of the surface tension data was not undertaken. An independent measurement of the zero-charge potential difference by the streaming-jet electrode technique [40] in the same system provided the value identical with the potential of the electrocapillary maximum. On the basis of the standard potential difference of —0.225 V for the tetrabutylammonium ion transfer, the zero-charge potential difference was estimated as equal to 8 10 mV [41]. 

However, the surface tension data that would confirm the specific adsorption of hydrophilic and semihydrophobic ions are lacking. Absence of the specific ion adsorption in these cases is corroborated by the analysis of the surface tension data for the nonpolar-... 

Until very recently, there has been little or no experimental protocol for obtaining quantitative dynamic surface tension data on monolayer films. In most cases, the experimental set-up has consisted of a simple Langmuir film balance equipped with a variable-speed motor to drive the moving barrier. Hysteresis data were then obtained at a number of compression/expansion rates and compared qualitatively. This experimental set-up was improved considerably by Johnson (Arnett et al., 1988a), who modified a special... 

Trioctylmethylammonium chloride [7] has been widely used as a phase transfer catalyst. This compound is slightly soluble in water and forms aggregates at very low concentrations (Okahata et al., 1977). Figure 3 shows surface tension data, which indicate aggregation occurring at 10-4-10-5 M. The dye probe method and conductance measurements suggest that the... 

Standard Free Energies of Adsorption of B and BH. The standard free energy of adsorption of C12BMG was calculated from the surface tension data in Figures 1 and 2 by use of the equation ... 

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 following are typical surface tension data of different solutions ... 

FIGURE 3.3 Surface tension data of a homologous series of short-chain acids in water. 

The surface tension data in the case of a homologous series of alcohols and acids show a simple relation to the alkyl chain length (Figure 3.3). It is observed that each addition of the -CH2- group gives values of concentration and surface tension such that the value of concentration is lower by about a factor 3. 

Evidence of attachment of an organic molecule to a metal surface by a particular group in the molecule is not only provided from surface tension data on the surface of liquid mercury but is also to be noted in the phenomenon of displacement of one liquid by another from a surface. The hydrocarbons adhere to metals much less tenaciously than molecules containing polar groups such as —COOH and —OH. Thus we find that a hydrocarbon may be removed from a metal surface by displacement with alcohol and also that the lubricating properties of a hydrocarbon are materially affected by the addition of hydrocarbon compounds containing polar groups (Hardy, Proc. Roy. 8oc. A, c. 650, 1922, A, ci. 487, 1923). 

These two equations present the extension of the Frumkin model to the adsorption of one-surfactant system with two orientational states at the interface. The model equations now contain four free parameters, including cou co2, and b. The equations are highly nonUnear, and regression used in the analysis of surface tension data involves special combinations of Eqs. 23 and 24, which produces a special model fimction used in the least-square minimization with measured surface tension data. Since the model function also contains surface... 

Fig. 4 Comparison between the experimental surface tension data for CnEs surfactant, data points [45], and the extended S-L adsorption model (line) by the aggregation of surfactant molecules at the sm-face described by Eq. 27-29. The best fit gives a>i = 557,691 m /mol, Tc = 1004.471 m /mol, and = 3.003...

The surface tension data given in Figure 3.5 was obtained for aqueous solutions of a trivalent cationic surfactant (C0RCI3) in both water and in 150 mM NaCl solution. Use the data and the Gibbs adsorption isotherm to obtain estimates of the minimum surface area per molecule adsorbed at the air/water interface. 

Figure 3.5 Surface tension data for aqueous solutions of a trivalent surfactant C0RCI3.

Results for the various binary mixed surfactant systems are shown in figures 1-7. Here, experimental results for the surface tension at the cmc (points) for the mixtures are compared with calculated results from the nonideal mixed monolayer model (solid line) and results for the ideal model (dashed line). Calculations of the surface tension are based on equation 17 with unit activity coefficients for the ideal case and activity coefficients determined using the net interaction 3 (from the mixed micelle model) and (equations 12 and 13) in the nonideal case. In these calculations the area per mole at the surface for each pure component, tOj, is obtained directly from the slope of the linear region in experimental surface tension data below the cmc (via equation 5) and the maximum surface pressure, from the linear best fit of... 

A second way of classifying the material is on the basis of the experimental methods involved. For mobile interfaces, surface tension is easily measured. For these it is easiest to examine the surface tension-adsorption relationship starting with surface tension data. When insoluble surface films are involved, we shall see how the difference in y between a clean surface and one with an adsorbed film may be measured directly. For solid surfaces, surface tension is not readily available from experiments. In this case adsorption may be measurable directly, and the relationship between adsorption and surface tension may be examined from the reverse perspective. 

EXAMPLE 7.4 Determination of Surface Excess Concentration from Surface Tension Data. The slope of the 25°C line in Figure 7.15 on the low-concentration side of the break is about -16.7 mN m 1. Calculate the surface excess and the area per molecule for the range of concentrations shown. How would Figure 7.15 be different if accurate measurements could be made over several more decades of concentration in the direction of higher dilution Could the data still be interpreted by Equation (49) in this case ... 

Neumann et al. have tabulated average values of experimentally determined Hamaker constants and then used surface tension data for the same systems to calculate d0 values for the following materials ... 

Molecular weight of a solute from tt versus A isotherms Use of the van t Hoff equation for monolayers Suppression of evaporation by monolayers Surface excess concentration from surface tension data... 

This measured concentration change is usually converted into a surface excess quantity, analogous to that usually calculable from surface tension data for adsorption at the liquid/vapor interface. In the case of... 

Hie International Critical Tables and Timmermans75 report surface tension data from 0Y to 60X for the compounds. Jasper reports duiu in the same temperature range.33 The data were extended over a wider temperature range by the method of Sugdcn.1... 

The objective in this section is to derive a mathematical model that can be used to extract the rate of adsorption from experimentally obtained dynamic surface tension data. Various investigators have speculated that the mechanism of surfactant adsorption involves two subsequent steps ... 

Equations D3.5.30 and D3.5.32 are both very valuable. They state that the rate of adsorption can be obtained from plots of the interfacial tension versus either tA- (for t—>0) or lth (for the long-term solution f— >). With these two equations the tool to extract the adsorption rate from experimentally obtained surface tension-time curves is at hand. It should be noted that instead of the Gibbs model, one could use one of the previously mentioned adsorption isotherms such as the Langmuir adsorption isotherm to convert interfacial tension to interfacial coverage data. The adsorption isotherms may be obtained by fitting equilibrium surface tension data versus surfactant concentration. 

The three EME coupling agents in Table 1 were analyzed using contact angle measurements to determine their polar and dispersion components of surface tension. From the surface tension data, wettability envelopes were constructed and compared with the surface tension properties of the epoxy coating [4], These data predicted that EME 47 would be wet by the epoxy, but not EME 23. This is believed to be the reason for the very low peel strength when EME 23 was employed [4],... 

From the surface tension data obtained for different electrolyte concentrations, the relative ionic surface excesses can be determined. Thus, for the cell Hgl KC1 (aqueous)IHg2Cl2lHg, from Eq. (1.69), the cation excess is given by... 

The Gibbs adsorption equation enables the extent of adsorption at a liquid surface to be estimated from surface tension data. 

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