Interaction between sodium dodecyl sulfate systems

Surfactant concentration (varied after polymerization) greatly affects the viscosity of associating polymer systems. Iliopoulos et al. studied the interactions between sodium dodecyl sulfate (SDS) and hydrophobically modified polyfsodium acrylate) with 1 or 3 mole percent of octadecyl side groups [85]. A viscosity maximum occurred at a surfactant concentration close to or lower than the critical micelle concentration (CMC). Viscosity increases of up to 5 orders of magnitude were observed. Glass et al. observed similar behavior with hydrophobically modified HEC polymers. [100] The low-shear viscosity of hydrophobically modified HEC showed a maximum at the CMC of sodium oleate. HEUR thickeners showed the same type of behavior with both anionic (SDS) and nonionic surfactants. At the critical micelle concentration, the micelles can effectively cross-link the associating polymer if more than one hydrophobe from different polymer chains is incorporated into a micelle. Above the CMC, the number of micelles per polymer-bound hydrophobe increases, and the micelles can no longer effectively cross-link the polymer. As a result, viscosity diminishes. 

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... 

The interaction between uncharged polymers and charged surfactants has been studied in a number of research articles. Jones (1967) studied the interaction in polyethylene oxide (PEO)/sodium dodecyl sulfate (SDS) systems. For a fixed amount of polymer concentration, the surfactant concentration... 

We have studied three model systems of five-component mixtures oil -water - surfactant - alcohol - salt. Three different ionic surfactants have been used dodecyltrimethyl ammonium bromide (DTAB), sodium dodecyl sulfate (SDS) and sodium hexadecyl benzene sulfonate (SHBS). The alcohol used was butanol its addition was necessary because the above surfactants alone could form microemulsions. The salt screened the electrostatic interactions between surfactant polar heads it reduced Cq In this way, a continuous structural evolution o/w - bicontinuous - w/o could be obtained by addition of salt. At each salinity, the size of the structural elements was the largest (maximum swelling Rq for droplets, bicontinuous structures) because the microemulsions coexisted with excess oil and/or water. 

---