Activation of surfactants

The catalytic activity of surfactant micelles and the effect of the concentration of reagents in micelle catalysis are tested on hydrolysis of esters of phosphorus acids [25],... 

Routledge, E.J. and Sumpter, J.P. (1996). Estrogenic activity of surfactants and some of their degradation products assessed using a recombinant yeast screen. Environmental Toxicology and Chemistry 15, 241-248. 

Furuse, K., Ishizeki, C., and Iwahara, S. Studies on spermicidal activity of surfactants. I. Correlation between spermicidal effect and physicochemical properties of p-menthanylphenyl polyoxyethylene (8.8) ether and related surfactants. J. Pharm. Dyn. 1983, 6, 359-372. 

Application of Activity at cmc. The above consideration suggested us to propose a new treatment for ionic micelle formation. According to thermodynamics, the micelle-monomer equilibrium is achieved when the chemical potential of surfactant in the micelle is equal to that in the bulk solution. The free energy of micelle formation can be represented by the use of the critical micelle activity, cma, which is the activity of surfactant at the cmc, as... 

The application of the activity of the surfactant has been examined also for the surface tension and adsorption of disodlum alkyl phosphate(6,7), sodium dodecyl sulfate(37), alkyl trimethylammonium bromide(35 ), and sodium perfluorooctanoate(13) solutions. These studies show that the surface tension and theadsorption amount are controlled by the activity of surfactant, irrespective of the added electrolyte concentration. 

The counterion activity of surfactant solutions rises linearly with concentration up to the region of the CMC while it takes on a slower increase above the CMC42). 

The primary factors Horn44 considers in his framework are gut length, gut pH, and microbial activity (Table 11.1). Besides these, other factors are also proving to be part of the complex mixture of variables that are important in herbivorous fish digestion. These other factors include specific endogenous and exogenous digestive enzymes in the gut, redox state, concentration, and activity of surfactants, and concentration and activity of cations. Gut transit time or evacuation rate is also considered an important factor because it influences assimilation efficiency and consumption rates.39-52-53... 

The surface activity of surfactant is one of the most commonly measured properties and can be quantified by the Gibbs adsorption equation ... 

The reasons for this impeded foam formation by organic liquids are not completely clear. Probably either the weak surface activity of surfactants in the organic liquids causes it or the fact that the steady-state (described above) of film surfaces is established slowly due to decelerated surfactant diffusion towards the liquid/gas inteffaces. The much smaller thickness (100-300 nm) of the films formed compared to the typical initial thickness of aqueous films (1 pm) speaks in favour of this assumption. The latter increases with the increase in the bulk surfactant concentration [53,73],... 

Figure 13.5 is an example of a collaborate activity of surfactant and filler in obtaining small and uniform cell sizes. The control foam was obtained with surfactant alone. The addition of silica increases nucleation and results in a very uniform polyurethane foam. This foam was developed to increase the insulation rating of refrigerator foams. ... 

Fig. 21. Surface activity of surfactants and polysoaps in water at 25 °C, exemplified by a cationic methacrylate + = polysoap 53, X = corresponding surfactant monomer. (Data taken from [245])...

Eq. (10.63) can be hilfilled at low and high surface activity of surfactant. It is not recommended to use a surfactant of very high smface activity (cf. condition (8.72)) in the absence of a rear stagnant cap since the adsorption layer is carried away to the rear pole of the bubble. Addition of such surfactant does not enhance particle deposition on the leading surface of bubbles and does not prevent their detachment from the rear surface. The surfactant molecules are concentrated in the close neighbourhood of the rear pole of the bubble and detachment of particles can occur from any part of the surface in the vicinity of which the normal velocity components are directed to the liquid. 

The surface activity of surfactants varies over a broad concentration range and hence a broad time interval has to be studied. Therefore, complementary experiments are necessary to cover the extensive time range from less than a millisecond up to minutes, hours and sometime days. The following Table 4.2 summarises the most frequently used surface tension methods, their available time and temperature intervals and suitability for studying the liquid/air and liquid/liquid interface. The given values represent the interval available by standard instruments, while particular modifications certainly allow to go beyond these limits. 

Tii3-nanoclusters (Fig. 2.8) have been used as powerful activators for heterogeneous noble metal hydrogenation catalysis [9, 130]. In the so-called butyronitrile hydrogenation standard test the activity of surfactant-stabiUzed colloidal rhodium... 

The parameter p in Eq. (41) considers that die adsorption activity of surfactant molecules is larger in state 1 than in state 2 (42,43) ... 

Temperature Stability The long-term thermal stability of injected surfactants in the reservoir environment is a must for an effective surfactant formulation. The thermal stability of several ionic and nonionic surfactants has been reported in terms of the time required for half of the surfactant to decompose (e.g. half-life).Most of the surfactants investigated decomposed by first-order kinetics. The interfacial activity of surfactant solutions after six months at 80°C was reported by Akstinat. The results showed that the stability of the surfactants was in the order ether sulfonates > ether carboximethylates > ether sulfates > ether phosphates. 

Because the activity of surfactants used below cannot reach their theoretical maximum as determined by the thermodynamics of surfactant aggregation (see also Chapter 15), they will also be unable to achieve their maximum degree of adsorption at the solution-vapor interface. It is therefore important to know the value of Tk for a given system before considering its application. Most surfactants, however, are employed well above their Krafft temperature, so that the controlling factor for the determination of their effectiveness will be the cmc. 

There appear to be only relatively minor variations in effect from one head group to another in anionic surfactants. The difference in cross-sectional area between sulfate and sulfonate groups does not appear to influence greatly the activity of surfactants in lowering surface tensions, although some difference can be noted when differences in cmc are taken into consideration. The... 

The activity of surfactants under pressure and the formulation of reverse micelles has been published by Johnston, Lemert and McFann in Am. Chem. Soc. Ser. 406 (1989). 

Equations 5-7 were solved for a series of appropriate Y values and the result expressed in molal concentration of surfactant monomer units as a function of the total surfactant ncen ation (c). In Figure 1, the mean ionic activity of surfactant (lA ] IK ])l/2 = a+, the concentration of the surfactant monomer anions, the counteMons, the polymer-surfactant complex and the free micelle vs. the total surfactant concentration are plotted. The parameters of Equations 5 and 6 were chosen such as to be characteristic for the sodium dodecyl sulfate and poly-(vinyl-alcohol) system = K= 2.7x10 , a = a = 0.3,... 

It is important to note that at cjyj, which frequently appears as a (second) breakpoint in some physico-chemical properties vs. surfactant concentration plots, and is regarded as the saturation value of polymer with surfactant, the polymer is not necessarily saturated. In the present example the bound amount of surfactant at c is only 11% of the saturation value. As a result of the micelle formation the surfactant activity increases very little above cjyj, consequently IcompLJ cannot further increase due to the constancy of the mean activity of surfactant. The equilibrium constants for the complex formation can be chosen so that at the beginning of the micelle formation the amount of surfactant in complex is close to that for saturation. In this case the mean activity of surfactant as a function of the total surfactant concentration shows an inflexion below cjvi. ... 

Ozone (0.8 ppm) affected the surface activity of surfactant in rats exposed for 2 or 12 h, whereas distinct morphological changes in bronchoalveolar lavage or in the surfactant subtypes were not observed (Putman et al. 1997). Adsorption experiments indicated that bronchoalveolar lavage from rats exposed for 12 h to O3 remained at lower equilibrium surface pressures than lavage from control rats. These observations suggest interference of in-... 

Due to the presence of the hydrophobic effect, surfactant molecules adsorb at interfaces, even at low surfactant concentrations. As there will be a balance between adsorption and desorption (due to thermal motions), the interfacial condition requires some time to establish. The surface activity of surfactants should therefore be considered a dynamic phenomenon. This can be determined by measuring surface or interfacial tensions versus time for a freshly formed surface, as will be discussed further below. 

The inhibition activity of surfactants can be also revealed from impedance data (Figure 9.26). Nyquist plots obtained for polyether-free solutions at open-circuit potentials are nothing else than lines that are observed over a nearly entire range of applied frequencies. In accordance with voltammetric data, Sn(II) reduction is mainly controlled by diffusive mass transport in this case. The addition... 

If it is assumed that the concentration of free monomers is low then the activity of surfactant monomer, as, may be replaced by the mole fraction of monomers Xs and Equation 3.11 becomes... 

There seems to be little more evidence in the literature to allow a more coherent discussion of the effects of surfactants on herbicide activity and explanation of their intrinsic phytotoxicity. It may be that with such a diversity of plant structures the task of rationalizing the activity of surfactants (with the complex pattern of wetting effects, evaporation retardation, solubilization, particle size alteration of precipitated active ingredient, membrane permeability effects and intrinsic biological effects on enzyme systems) will be more daunting than with the relatively simple problem that must be faced with surfactant effects on the human organism. It is likely, however, that study of surfactant effects on plant cells will give useful information to help in the elimination of effects on mammalian cells. 

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