Surfactant dynamic behavior

Choi and Funayama [19] also measured sodium atom emission from sodium dodecylsulfate (SDS) solutions in the concentration range of 0.1-100 mM at frequencies of 108 kHz and 1.0 MHz. The sodium line intensity observed at 1 MHz was nearly constant in the concentration range from 3 to 100 mM and was considerably higher than that at 108 kHz. This frequency dependence of the intensity is opposite that for NaCl aqueous solution. The dynamical behavior of the absorption and desorption of surfactant molecules onto the bubble surface may affect the reduction and excitation processes of sodium atom emission. This point should be clarified in the future. 

Although RMs are thermodynamically stable, they are highly dynamic. The RMs constantly colhde with each other and occasionally a colhsion results in the fusion of two RMs temporarily. During this fusion surfactant molecules and the contents residing inside RMs may be exchanged. In AOT reverse micellar system, this dynamic behavior exhibits second-order kinetics with rate constants in the order of 10 to 10 M s [37]. This dynamic nature not only influences the properties of the bulk system but also affects the enzymatic reaction rates [38]. 

Dekker et al. [170] have also shown that the steady state experimental data of the extraction and the observed dynamic behavior of the extraction are in good agreement with the model predictions. This model offers the opportunity to predict the effect of changes, both in the process conditions (effect of residence time and mass transfer coefficient) and in the composition of the aqueous and reverse micellar phase (effect of inactivation rate constant and distribution coefficient) on the extraction efficiency. A shorter residence time in the extractors, in combination with an increase in mass transfer rate, will give improvement in the yield of active enzyme in the second aqueous phase and will further reduce the surfactant loss. They have suggested that the use of centrifugal separators or extractors might be valuable in this respect. 

From such microbubble-dissolution measurements, Bemd (ref. 16,17) outlined a physical model to explain much of the dynamic behavior of film-stabilized microbubbles.- One problematic aspect of this dynamic behavior involved the question of how a gas nucleus can be surrounded by a relatively impermeable film and yet subsequently act to produce cavitation when a gas/water interface is needed to initiate cavitation. Bernd (ref. 16) explains that if the stabilized gas microbubble enters a low-pressure area, the gas within the microbubble will attempt to expand. The surfactant film may also elastically attempt to expand. The surfactant film will then be expanded until essentially the surface tension of the water alone acts to contract the microbubble, since the protective shell no longer acts. The film has either been ruptured upon expansion, or it has expanded until it is ineffectual. Thus the microbubble (i.e., gas nucleus) should be capable of expanding to form a cavitation void or acquire additional gas in the form of water vapor or from surrounding dissolved gas. In addition, Bernd points out that it is reasonable to expect a gas microbubble to acquire such an effective... 

Zourab, S.M. and Miller, C.A., Equilibrium and dynamic behavior for systems containing nonionic surfactants, w-hexadecane, triolein, and oleyl alcohol. Colloids Surf. A, 95, 173, 1995. 

Raney, K.H. and Miller, C.A., Diffusion path analysis of dynamic behavior of oil-water-surfactant systems, A/C 33, 1791, 1987. 

Thus, the situation is much more complex if the characteristics of the reverse micellar system (e.g., aggregation, micellar concentration, and dynamic behavior) are functions of time. In light of the available results, no definitive explanation can be offered at this time to account for the remarkable monodispersity obtained at intermediate R values, at which maximum number of nuclei is formed. Quantitative evaluation of the main features of the proposed model must await further experimental data. Of particular interest in this connection are the development of a quantitative description of the nuclei-aggregation process and the determination of surfactant aggregation numbers with water-ethanol mixtures as aqueous solubilizate. 

Although much work has been done to study equilibrium behavior in surfactant systems many nonequilibrium dynamic behavior are still far from well understood. When neat or concentrated surfactant is contacted with solvent complicated diffusion process occurs due to the presence of mesophase at the interface. Initially, at the interface, the formation, type and structure of the mesophase will influence the subsequent dynamics. In some cases the interface can become unstable during dissolution and rather striking instabilities form. To obtain a good understanding of such complicated nonlinear processes has relied on a systematic study of the equilibrium phase behavior in such systems. This has given us a firm basis on which to study the nonequilibrium behavior. 

Surfactants play an important role in the formation and stability of foams. Investigators have determined foam stability by measuring the half-life (e.g. t 2) the foam. Half-life is the time required to reduce foam voLume to half of its initial value. It has been demonstrated that the foam stability (i.e.half-life) decreased with increasing temperature, whereas the foaminess of the surfactant solution increased with temperature. It is likely that these properties of foam depend on the molecular structure and concentration of the surfactant at the gas/liquid interface. Comparison of the results of static foam stability with that of the dynamic behavior of foam in porous media revealed that the foam stability is not required for efficient fluid displacement or a decrease in the effective air mc >ility in a porous medium. Moreover, the ability of the surfactants to produce in-situ foam was one of the important factors in the displacement of the fluid in a porous medium. 

As the reservoir temperature is higher than the embient temperature, the foam properties were studied at 50 C. The experimental data for various commercial surfactants are recorded in Tables IV and V. The foamability of the first four Alfonic surfactants (Table-I) at 0.1 wt% concentration is considerabily reduced at 50 C as compared to ambient temperature due to the variation in the dynamic behavior of the surfactants at higher temperatures. 

The first four chapters thus provide a general background on interfacial phenomena, colloidal dispersions, and surfactants, with emphasis on their equilibrium properties. The remaining chapters deal with the dynamic behavior of interfaces, emphasizing this subject to a much greater degree than most books on interfacial phenomena. 

Lim, J.-C. and Miller, C.A., Dynamic behavior and detergency in systems containing nonionic surfactants and mixtures of polar and nonpolar oils, Langmuir, 7, 2021, 1991. 

The influence of amphiphiles on interfacial properties interfacial tension, wetting behavior, dynamical aspects such as the question of how small amounts of surfactant influence the kinetics of phase separation. 

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