Sodium dodecyl sulfate energy

In accordance with Equation 22, the values of log cmc + (Pll/-) log f+ are also plotted against log[X] in the same figure. Thelinear relations obtained now give slopes of -0.9 for sodium dodecyl sulfate and potassium dodecanoate, and -1.8 for disodium dodecyl phosphate, which are in fairly good agreement with the theoretical values of -1 and -2, respectively. The results obtained here suggest that the condensation of counter ions on the ionic micellar surface and the reduction of electrostatic energy play important roles in the ionic micelle formation. 

Rgure 2.37. Energy of adhesion between hexadecane droplets stabilized in water by sodium dodecyl sulfate (SDS). The energy of adhesion is much greater with KCl than with NaCl or LiCl, although the KCl concentration is lower. (Adapted from [110].)... 

FORMATION. Aqueous solutions of highly surface-active substances spontaneously tend to reduce interfacial energy of solute-solvent interactions by forming micelles. The critical micelle concentration (or, c.m.c.) is the threshold surfactant concentration, above which micelle formation (also known as micellization) is highly favorable. For sodium dodecyl sulfate, the c.m.c. is 5.6 mM at 0.01 M NaCl or about 3.1 mM at 0.03 M NaCl. The lower c.m.c. observed at higher salt concentration results from a reduction in repulsive forces among the ionic head groups on the surface of micelles made up of ionic surfactants. As would be expected for any entropy-driven process, micelle formation is less favorable as the temperature is lowered. 

Where this factor plays a role, the hydrophobic interaction between the hydrocarbon chains of the surfactant and the non-polar parts of protein functional groups are predominant. An example of this effect is the marked endothermic character of the interactions between the anionic CITREM and sodium caseinate at pH = 7.2 (Semenova et al., 2006), and also between sodium dodecyl sulfate (SDS) and soy protein at pH values of 7.0 and 8.2 (Nakai et al., 1980). It is important here to note that, when the character of the protein-surfactant interactions is endothermic (/.< ., involving a positive contribution from the enthalpy to the change in the overall free energy of the system), the main thermodynamic driving force is considered to be an increase in the entropy of the system due to release into bulk solution of a great number of water molecules. This entropy... 

A predictive molecular thermodynamics approach is developed for microemulsions, to determine their structural and compositional characteristics [3.7]. The theory is built upon a molecular level model for the free energy change. For illustrative purposes, numerical calculations are performed for the system water, cyclohexane, sodium dodecyl sulfate as surfactant, pentanol as cosurfactant and NaCl as electrolyte. The droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in the droplets, and the distribution of the components between droplets and the continuous phase are calculated. The theory also predicts the transition from a mi-... 

The activation parameters for the acid-catalyzed hydrolysis of long chain alkyl sulfates compared to those for non-micellar ethyl sulfate calculated from potentiometric data indicate that the rate acceleration accompanying micellization is primarily a consequence of a decrease in the enthalpy of activation rather than an increase in the entropy (Kurz, 1962). However, the activation energies for the acid-catalyzed hydrolysis of sodium dodecyl sulfate calculated from spectrophotometric data have been reported to be identical (Table 8) for micellar and non-micellar solutions, but the entropy of activation for the hydrolysis of the micellar sulfate was found to be 6 9 e.u. greater than that for the non-micellar system (Motsavage and Kostenbauder, 1963). This apparent discrepancy may be due to the choice of the non-micellar state as the basis of comparison, i.e. ethyl sulfate and non-micellar dodecyl sulfate, to temperature dependent errors in the values of the acid catalyzed rate constant determined potentiometrically, or to deviations in the rate constants from the Arrhenius equation. 

Sprrmger L, Acree WE, Abraham MH (2007) Linear free energy relationship correlation of the distribution of solutes between water and sodium dodecyl sulfate (SDS) micelles and between gas and sds micelles. J Chem Inf Model 1808-1817... 

The first term on the right-hand side of equation (8.7) is the contribution of the head group repulsion, while the second is the interfacial energy contribution where Ahg is the total surface area of the head groups and (Tmic is the interfacial tension. Within the framework of the Gouy-Chapmann theory, the dressed micelle model allows the estimation of values, which are for sodium dodecyl sulfate (SDS), sodium octyl sulfate, and teradecyltrimethylammonium bromide, 15-16, 11 and 11-14 mN m , respectively (15). Note that these values are up to a factor of 3 lower than those of the pure monomers (cf. Table 8.2). A further decrease of or is possible in the case of emulsions of organic liquids where the interface is saturated with stabilizer. For example, a value of about 4 mN m was determined for a toluene emulsion stabilized with potassium lau-rate (16). 

In a systematic study, the emulsification of paraffin oil (77d = 32 mPa s) in water with an oil volume fraction of 0.1, in the presence of 50 mM sodium dodecyl sulfate (SDS) as emulsifier at 20°C was investigated in various agitation machines (32). The interfacial tension in this particular system was determined to be 7 mN m The conditions were adjusted in such a way that the diminution energy (VFv) in each machine was equal to 5 X 10 J m . The diminution energy is defined as the power input per volume. The data presented in Table 8.6 reveal, on the one hand, how different the necessary condition are for the different devices to achieve the same and on the other hand, the influence of the geometry of the device on the droplet size distribution. 

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