Ordered surfactant interactions, types

One complication that arises with thin-liquid foam film studies is the need to have surface-active components present in order to stabilize the films. Without adequate film stability, measmement of the interactions between the two air-water interfaces caimot be accomplished. These surface-active species provide film stability via surface elasticity and repulsive force interactions between the interfaces (i.e., DLVO-type interactions). In addition, surfactants may interact with polymers added to the system, which can mediate and change the polymer configuration, surface adsorption, and thin-film interactions. Therefore, to determine the role of a polyelectrolyte one must understand independently the various interfacial and polymer-surfactant interactions. Theodoly and colleagues [18,19] have accomplished this through a judicious choice of combined polymer-surfactant mixtures. Two systems... 

In order to assess the effect of compression (expansion) on more complex mixed layers (protein + protein or protein + surfactant), we have simulated four different binary systems. The mixtures are composed of two species of the same spherical size in a 1 1 molar ratio. In all cases, one of the species (Type 1) interacts solely through the repulsive core potential both with particles of its same type and with particles of Type 2. The Type 2 particles, however, are able to form bonds with particles of their ovm type. The four different cases correspond to different classes of bonding between the particles of Type 2 (a) no bonds, (b) very-easy-to-break bonds (fcmax = 0-3)i (c) breakable bonds (fcmax = 0-5), and (d) permanent bonds (fcmax = °°)-The structures of fhe four differenf sysfems after 6 X 10 equilibration time steps are shown in Figure 23.3. Case (a) represents a perfect mixture since... 

The interaction between the two surfactants is mainly due to electrostatic forces. The strength of attractive electrostatic interaction decreases in the order anionic-cationic > anionic-zwitterionic capable of accepting a proton > cation-zwitterionic capable of losing a proton > anionic-POE nonionic > cationic-POE nonionic. Mixtures of surfactants of the same charge type (anionic-anionic, cationic-cationic, nonionic-nonionic, zwitterionic-zwittenonic) show only very weak interaction (negative p values of 1 or less) at the aqueous solution-air interface, although they can show significant interaction at other interfaces. 

Surfactants in solutions show a broad variety of microstructures caused by molecular selforganisation. The observed structures depend essentially on the physical interactions of the involved components and the composition of the mixtures. For the selection of a suitable type of reaction medium the required composition of the reaction mixture is more important than the question of whether a micellar solution, a bicontinuous microemulsion, a w/o- or an o/w-microemulsion is formed. For synthetic purposes high concentrations of reactants are indispensable in order to avoid high-energy cost for work-up procedures. Therefore, a reaction system that allows high-reactant concentrations needs to be chosen. For stoichiometric reactions involving reactant incompatibility, like nucleophilic substitution reactions with an inorganic nucleophile, often an aqueous solution of this reactant has... 

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