Surface tension dynamic measurement

Howell, E. 2001. Dynamic surface tension measurements of liquid solder using oscillating jets of elliptical cross section. Mechanical and Industrial Engineering. University of Illinois at Chicago, Chicago, IL. pp. 75. 

Avranas, A. and Tasapoulus, V. Aqueous solutions of sodium deoxycholate and hydroxypropylmethylcellulose dynamic surface tension measurements, /. Colloid Interface Sci, 221, 223, 2000. 

Various experimental methods for dynamic surface tension measurements are available. Their operational timescales cover different time intervals. - Methods with a shorter characteristic operational time are the oscillating jet method, the oscillating bubble method, the fast-formed drop technique,the surface wave techniques, and the maximum bubble pressure method. Methods of longer characteristic operational time are the inclined plate method, the drop-weight/volume techniques, the funnel and overflowing cylinder methods, and the axisym-metric drop shape analysis (ADSA) " see References 54, 55, and 85 for a more detailed review. 

Several workers have also commented on the possibility of using dynamic surface tension measurements on the fountain solution as being more realistic in view of the fast printing speeds used. This might also make measurements of dampening solutions containing surface active agents correlate better with actual press performance due to the rate of diffusion of materials to the surfaces of these fluids. 

The Marangoni elasticity can be determined experimentally from dynamic surface tension measurements that involve known surface area changes. One such technique is the maximum bubble-pressure method (MBPM), which has been used to determine elasticities in this manner (24, 26). In the MBPM, the rates of bubble formation at submerged capillaries are varied. This amounts to changing A/A because approximately equal bubble areas are produced at the maximum bubble pressure condition at all rates. Although such measurements include some contribution from surface dilational viscosity (23, 27), the result will be referred to simply as surface elasticity in this work. 

Adsorption kinetics, mainly studied by dynamic surface tension measurements, shows many features very much different from that of typical surfactants (Miller et al. 2000). The interfacial tension isotherms for standard proteins such as BSA, HSA, (3-casein and (3-lactoglobulin were measured at the solution/air interface by many authors using various techniques. The state of the art of the thermodynamics of adsorption was discussed in Chapter 2 while isotherm data for selected proteins were given in the preceding Chapter 3. Here we want to give few examples of the dynamic surface pressure characteristics of protein adsorption layers. 

Experimental results for solutions of other Tritons have been reported in Ref 113. From these studies it was concluded that the distribution coefficient for Triton X-45 is significantly higher than for Triton X-405. To visualize the significant differences in dynamic surface tensions measured for the three cases discussed above, the results of experiments with Triton X-45 are reported in Fig. 9. It is obvious that for case 3 the adsorption process is flie fastest as adsorption takes place from both adjacent liquid phases. 

Acknowledgment We would like to thank Dr. Kai Koppen for performing the kinetic measurements and most of the spreading tests, Wayne Kennedy for dynamic surface tension measurements. Prof. Heinz Rehage (University Essen) for many fruitful discussions and the Video Enhanced-Microscopy investigations in his laboratory, and Dr. Krystina Kratzat for help with the polarization microscopy. 

The dynamic surface tension measurements performed in phosphate buffer solutions (pH 6.0,1 = 0.05 M) at constant lysozyme concentration, 5.1x10 M, and varying concentrations of MR, show that the LYS-MR mixture is characterized by more high rate of adsorption and more low quasi-equilibrium surface tension, than pure LYS (Fig. 1). As concerning the effect of MR on the surface activity of lysozyme, it is seen from Fig. 2 that MR enhances it at all using concentration-making lysozyme more hydrophobic. MR critical micelle concentration in lysozyme presence is 32.7 mM. 

Table 2.2 Dynamic Surface Tension Measurement Methods for Liquids ...

Fig. 1 Diffusion-limited adsorption exhibited by non-ionic surfactants. Four examples for dynamic surface tension measurements are shown decyl alcohol at concentration 9.49 x 10" M (open circles) adapted from ref. [17] Triton X-100 at concentration 2.32 x 10 M (squares) adapted from ref. [8] CiaEOg at concentration 6 x 10 M (triangles) and CioPY at concentration 4.35 x 10 M (solid circles), both adapted from ref. [18]. The asymptotic t dependence shown by the solid fitting lines is a footprint of diffusion-limited adsorption...

After having gained some experimental experience, Heyrovsky simplified KuCera s method by measuring the drop-time of several drops under constant mercury pressure instead of collecting and weighing each time 80 drops of 2-second duration. However, even after 3 years of tedious work, he could not reconcile the results of the dynamic surface tension measurements with those of the static method. 

Using this model, it is possible to determine rates for micellar breakdown from dynamic surface-tension measurements. The first attempt to do so was by Lucassen in 1975 [27], with mixed conclusions abont the resnlts and the validity of the model. Later, Rillaerts and Joos [28] were able to determine rate constants for micelle breakdown with cationic ammonium bromide surfactants, fonnd to be on the order of -200 S" for cetyltrimethylammonium bromide. In a significant review of the area, Noskov [29] concludes that due to the large number of experimental parameters associated with the model, numerical solution is difficult, and hence the rate information gained realistically only represents a rough approximation. A better approach was proposed... 

In practice, the model describes the situation where, according to the surface coverage, adsorbed molecules may rotate or change their conformation, varying their occupation area. The validation of this model has been given for some systems by using dynamic surface tension measurements acquired by the drop shape analysis [40, 41],... 

For a series of anionic surfactants with the same ionic head group, the life time of a micelle decreases with decreasing alkyl chain length of the hydrophobic component. Branching of the alkyl chain could also play a notable role in the life time of a micelle. Consequently, dynamic surface tension measurements need to be performed when selecting a surfactant as an adjuvant as this may have an important influence on spray retention. 

The maximum bubble pressure technique has been developed in various directions over recent years. One of the most promising of these is the use of this measurement technique in medicine. In a recent book, the capacity of dynamic surface tension measurements is shown as a new diagnostic tool, as well as for monitoring therapies in medicine (2). Quite a number of statistically significant relationships between selected surface tension values and biochemical data have been proven to exist. 

One way to circumvent the problem raised above is to measure the dynamic surface tension, instead of the equilibrium surface tension (described so far). The dynamic surface tension is the surface tension measured at short times after a surface has been formed and hence it is a non-equilibrium property. If an imaginary cut is made through a liquid and the molecules are not allowed to relax into an equilibrium state, the surface tension at the cut section will be the arithmetic average of the surface tensions of the present components. After equilibrium is reached, however, the most surface-active species, the one with the lowest surface tension, will be found in excess at the liquid/air surface. This relaxation of the surface tension, from an arithmetic mean to an equilibrium surface tension, is called the dynamic surface tension. If the surface tension is measured at short times after a surface has been formed, it reflects the surfactant bulk concentration, without the preferential adsorption of the more surface-active species which are present in small amounts. Hence, dynamic surface tension measurements are preferred for determining... 

In many experimental techniques used for dynamic surface-tension measurements (such as the MBP method and the drop-volume method [14,76,82]), the surface expands gradually with time. In such a case, the convective terms in Eqs. (24) and (25) carmot be neglected. Nevertheless, it can be demonstrated that with the help of the new independent variables. 

When the diffusion time has comparable magnitude with the time of formation of the electric double layer, the quasiequilibrium model is not applicable. Lucassen et al. [Ill] and Joos et al. [112] established that mixtures of anionic and cationic surfactants diffuse as a electroneutral combination in the case of small periodic fluctuations of the surface area consequently, this process is ruled by the simple diffusion equation. The e/ec ro-diffusion problem was solved by Bonfillon et al. [113] for a similar case of small periodic surface corrugations related to the capillary-wave methods of dynamic surface-tension measurement. 

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