Dynamic surface tension of surfactant

The maximum bubble pressure technique is a classical method in interfacial science. Due to the fast development of new technique and the great interest in experiments at very small adsorption times in recent years, commercial set-ups were built to make the method available for a large number of researchers. Rehbinder (1924, 1927) was apparently the first who applied the maximum bubble pressure method for measurement of dynamic surface tension of surfactant solutions. Further developments of this method were described by several authors (Sugden 1924, Adam Shute 1935, 1938, Kuffiier 1961, Austin et al. 1967, Bendure 1971,... 

One of the oldest experimental methods for the measurement of dynamic surface tensions of surfactant solutions is the oscillating jet (OJ) method. The idea is based on the analysis of a stationary jet issuing from a capillary pipe into the atmosphere which oscillates about its... 

The system volume Vs has even stronger effects on the dynamic surface tension of surfactant solutions. For a system volume Vs = 1.5 cm the error in the measured y values, as compared with the value for Vs = 20.5 cm, is 5 to 10%. The results of systematic studies presented elsewhere (V.B. Fainerman and R. Miller 2003) can serve as a guide for a rational choice of the measuring system volume which ensures precise measurement of the lifetime and surface tension. The optimum system volume, if all factors are taken into account, is that for which the ratio of system to bubble volume Vs/Vb is in the range between 2.000 and 5000. 

Otis, D. R., E. P. Ingenito et al. 1994. Dynamic surface-tension of surfactant Ta - experiments and theory. lAppl Physiol 77(6) 2681-2688. 

Figure 3.8 shows the dynamic surface tension of a pure anionic and a non-ionic surfactant dependent on the absorption time after the creation of new surface for different concentrations [9]. For both surfactants, the time dependence of the surface tension is greatly reduced when the concentration increases and this effect is especially pronounced when the critical micelle concentration is reached. The reason for this dependence is the diffusion of surfactant molecules and micellar aggregates to the surface which influences the surface tension on newly generated surfaces. This dynamic effect of surface tension can probably be attributed to the observation that an optimum of the washing efficiency usually occurs well above the critical micelle concentration. The effect is an important factor for cleaning and institutional washing where short process times are common. 

The expression o = Oq- kTJ, with J given in Table 5.2, can be used for description of both static and dynamic surface tension of ionic and nonionic surfactant solutions. The surfactant adsorption isotherms in this table can be used for both ionic and nonionic surfactants, with the only difference that in the case of ionic surfactant the adsorption constant K depends on the subsurface concentration of the inorganic counterions see Equation 5.48 below. 

Can these results for water sorption be related to the application of fountain solution to paper during lithographic printing In Figure 16 the addition of a surfactant is seen to have little effect on the dynamic surface tension of water at a surface age of 3 ms. Thus, on the time scale of the wetting of newsprint, fountain solutions which consist principally of an aqueous solution of gum arable may behave similarly to the case of water alone. Conversely, as shown in Figure 17 fountain solutions containing isopropanol exhibit lower dynamic surface tensions and should wet paper more readily than water alone. 

The presence of impurities in surfactant solutions can give very misleading results. In a recent paper, experimental dynamic surface tensions of sodium dodecyl sulphate (SDS) solutions were interpreted by Fainerman (1977) on the basis of a mixed diffusion-kinetic-controlled adsorption model. As the result a rate constant of adsorption k j as a function of time was obtained (cf. Fig. 5.5, ), although this parameter was assumed to be a constant. 

Irregularities in dynamic surface tensions of adsorption layers of soluble surfactants were discussed by Lucassen-Reynders (1987) in terms of aggregation phenomena of adsorbed molecules. She gave a theoretical model for the frequency spectrum of surface dilational properties. 

The graphs shown in Fig. 4.35 are the dynamic surface tensions of three mixtures of CioDMPO and CmDMPO measured with the maximum bubble pressure method MPT2 (O) and ring tensiometer TE2 (O). Although there is a general theoretical model to describe the adsorption kinetics of a surfactant mixture, model calculations are not trivial and a suitable software does not exists. 

The situation changes for non-equilibrium systems. The dynamic surface properties of micellar solutions depend strongly on the concentration in a broad range of surface life time and/or of the frequency of surface compression and dilation. First of all this is related to the fact that the adsorption rate of surfactants increases with concentration for both sub-micellar and micellar solutions. As an example, dynamic surface tensions of SDS in 0.1 M NaCl measured by Fainerman and Lylyk [77] are shown in Fig. 7. As one can see entirely different values of the dynamic surface tension and of the adsorption can correspond to the same surface age at c > CMC. 

The results of the preceding section allow us now to move on to describe the surfactant transport from the depth of the bulk phase to the interface or in the opposite direction. If any adsorption barriers are absent, this process determines the adsorption and desorption rates. The main step in the solution of this problem consists in the formulation of the surfactant diffusion equations for micellar solutions. The problem of surfactant diffusion to the interface was considered and solved for the first time by Lucassen for small perturbations [94]. He used the simplified model (5.146) where micelles were assumed to be monodisperse and the micellisation process was regarded as consisting of one step. Later Miller solved numerically the problem of adsorption on a fresh liquid surface using the same assumptions [146], Joos and van Hunsel applied also the same model to the interpretation of dynamic surface tension of... 

Shin JY, Abbott NL. 1999. Using light to control dynamic surface tensions of aqueous solutions of water soluble surfactants. Langmuir 15 4404 4410. 

The dynamic surface tension is an important property, relevant to many practical, non-equilibrium processes such as emulsification and foaming. Dynamic surface tension is a measure of how fast, in the millisecond range, a surfactant decreases the surface tension from the value of pure water (around 70 mN/m) to values in the range of 30 mN/m. It has been found that the type of spacer governs the dynamic surface tension of geminis to a considerable degree, i.e. the longer and... 

Thermodynamics of Surfactant Adsorption Kinetics of Surfactant Adsorption Dynamic Surface Tension of Solutions Drop and Bubble Shape Experiments Adsorption Behaviour of Mixed Systems... 

Dynamic surface tensions of a mixed surfactant system... 

The graph in Fig. 41 shows the dynamic surface tensions of a mixtured solution of CioDMPO and C14DMPO measured with the maximum bubble pressure method BPAl (O) and profile analysis tensiometer PATl ( ). The theoretical curves shown were calculated due to the adsorption kinetics model for surfactant mixtures discussed above (Miller et al. 2003). 

Figure 42. Dynamic surface tensions of a mixture of CiqDMPO and C14DMPO concentration ratio Cio I Ci4 = 10 mol/cm 110 mol/cm (O ), 10 mol/cm 1310 mol/cm (AA), 210 mol/cm 13 10 mol/cm ( ) solid lines - calculated for D = 1 10 (1), 310 (2) 210 (3) cmV using the surfactant parameters given in Figs. 38 and 39, open symbols - BPAl, closed symbols - PATl...

Bonfillon, A., Sicoli, E, and Langevin, D., Dynamic surface tension of ionic surfactant solutions, J. Colloid Interface Sci., 168, 497, 1994. 

Daniel, R.C. and Berg, J.C., Dynamic surface tension of polydisperse surfactant solutions a pseudo-single-component approach, Langmuir, 18, 5074, 2002. 

Miller, R., Aksenenko, E.V., Liggieri, L., Ravera, E, Ferrari, M., and Fainerman, V.B., Effect of the reorientation of oxyethylated alcohol molecules within the surface layer on equilibrium and dynamic surface pressure, Langmuir, 15, 1328, 1999. Mulqueen, M., Datwani, S.S., Stebe, K.J., and Blankenstein, D., Dynamic surface tensions of aqueous surfactant mixtures experimental investigation, Langmuir, 17, 7494, 2001. 

Surfactants that impact the dynamic surface tension of the pesticide can impact spray drift Generally, these are included within the formulation rather than tank mixed at application. 

A sprayed droplet hitting a leaf can result in one of two actions. Either the droplet will hit the leaf and spread to form a layer on the leaf, or the droplet will strike the leaf and recoil to bounce off. Surfactants can have an impact on this behavior, and the dynamic surface tension of the droplet can aid in reducing droplet bounce. The dynamic surface tension is important, since the concentration of surfactants above the critical micelle concentration of the surfactant is the important parameter in determining recoil. Small droplets are retained better than larger droplets, and droplets with surface tensions significantly less than water will also be retained better [35,36]. 

Zimoch, J., Hreczuch, W., Trathnigg, B., Meissner, J., Bialowas, E., Szymanowski, J. 2002. Detergency and dynamic surface tension of oxyethylated fatty acid methyl esters. Tenside Surfact. Det. 39 8-16. 

Fig. 5 Diffusion-limited adsorption exhibited by ionic surfactants with added salt Dynamic interfacial tension between an aqueous solution of 4.86 X 10 M SDS with 0.1 M NaCl and dodecane (open circles and left ordinate), adapted from ref. [13] Dynamic surface tension of an aqueous solution of 2.0xl0 M SDS with 0.5 M NaCl (squares and left ordinate), adapted from ref. [30] Surface coverage deduced from second-harmonic-generation measurements on a saturated aqueous solution of SDNS with 2% NaCl (filled circles and right ordinate), adapted from ref. [31]. The asymptotic dependence shown by the solid fitting lines is a footprint of diffusion-limited adsorption...

Fig. 3 Dynamic surface tension of an aqueous solution of 0.3 tnM (0.1 M LijSO, pH 2, 20°C) measured during the repeated cycling of the surfactant between oxidation states. The high values of surface tension correspond to a solution of and the low values correspond to a solution of IF...

FIG. 6 Dependencies of dynamic surface tension of the retreating meniscus (curve 1) and corresponding concentration of EOjo surfactant solution near to the meniscus Cm (curve 2) on flow rate v in a quartz capillary, r = 5 pm. By dotted line (curve 3) the results of calculation of the ratio Cm/Co using Eq. (8) are shown. 

Next, turning briefly to cylindrical aggregates, we may first remind the reader of the well-known instability of liquid jets that was analyzed early on by Bohr [41] among others, with the purpose of quantifying dynamic surface tensions of interfacial systems out of equilibrium. The question hence arises about what molecular mechanisms in the end allow rod-shaped surfactant micelles and cylindrical microemulsion droplets to really exist. 

In Ref [114], an approach to the dynamics of ionic surfactant adsorption was developed, which is simpler as both concept and application, but agrees very well with the experiment. Analytical asymptotic expressions for the dynamic surface tension of ionic surfactant solutions are derived in the general case of nonstationary interfacial expansion. Because the diffusion layer is much wider than the EDL, the equations contain a small parameter. The resulting perturbation problem is singular and it is solved by means of the method of matched asymptotic expansions [115]. The derived general expression for the dynamic surface tension is simplified for two important special cases, which are considered in the following section. 

The characterisation of the dynamic surface tension in surfactant systems is very important, both from a technological point of view and to understand the adsorption mechanism. 

The dynamic surface tension of [3-casein solutions at three concentrations 5 10, 10 and 10 mol/1 are shown in Fig. 14. As one can see the results from the two methods differ significantly. For the bubble the surface tension decrease starts much earlier. The surface tensions at long times, and hence the equilibrium surface tension from the bubble experiment are lower than those from the drop. However, the establishment of a quasi-equilibrium for the drop method is more rapid at low (3-casein concentrations while at higher P-casein concentrations this process is more rapid for the bubble method. This essential difference between solutions of proteins and surfactants was discussed in detail elsewhere [50]. In brief, it is caused by simultaneous effects of differences in the concentration loss, and the adsorption rate, which both lead to a strong difference in the conformational changes of the adsorbed protein molecules. 

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