Double-chain ionic surfactants

Lawrence, M.J., S.M. Lawrence, and D.J. Barlow. 1997. Aggregation and surface properties of synthetic double-chain-ionic surfactants in aqueous solution. J Pharm Pharmacol 49 594. 

In this connection, it should be noted that typical single-chain ionic surfactants are too hydrophilic to form balanced microemulsions under most conditions of interest, and we must either add a lipophilic cosurfactant such as pentanol or hexanol or use a double-chain ionic surfactant instead. Of course, cosurfactants can also be used with nonionic surfactants. It should be recognized that the size and shape of aggregates in a microemulsion are influenced by cosurfactant incorporated into the surfactant films but not by that dissolved in oil and water, whether in the microemulsion itself or in coexisting excess phases. The same is true for nonionic surfactants themselves, which... 

However, using double-chain ionic surfactants, e.g. sodium-bis-ethylhexylsulfo-succinate (AOT) [9, 67] and didodecyl dimethyl ammonium bromide (DDAB) [68], no co-surfactant is necessary to time the mean curvature of the amphiphilic film from positive to negative. In the following the quaternary (pseudo-ternary) system H20/NaCl (A)-n-decane (B)-AOT (D) will be discussed to show the main features of ionic microemulsions. Subsequently, the knowledge gained for alkylpolyglucoside micro emulsions (see Section 1.2.3) will be applied to understand the complex behaviour of five component ionic mixtures. 

Chung, Y.-C., Regen, S. L. (1993). Counterion control over the barrier properties of bilayers derived from double-chain ionic surfactants, Langmuir, 9 1937. 

Akay G., Wakeman R.J. 1994. Mechanism of permeate flux decay, solute rejection and concentration polarisation in crossflow filtration of a double chain ionic surfactant dispersion, J. Membr. Sci., 88, 177-195. 

Experimentally, the bending elastic modulus K as measured by ellipsometry is indeed found to be on the order of (0.1-1)A 7 for quite a wide range of microemulsion systems see, e.g.. Ref. 45 for a system with a single-chain ionic surfactant plus cosurfactant. Ref. 46 for a system with a double-chain ionic surfactant in which the chain length of the oil (linear alkane) is varied, and Ref 47 for a system with a nonionic surfactant in which the chain length of the surfactant is varied. 

Systems of a double-chain ionic surfactant in the presence of electrolyte, where the spontaneous curvature is controlled by temperature [45] (Fig. 11). 

Patrick, H.N. and Warr, G.G. (19%) Self-Assembly Patterns in Double and Triple Chained Ionic Surfactants, Chapter 2 in Specialist Surfactants, I.D. Robb (Ed.), Blackie Academic and Professional, Glasgow. 

The conditions for surfactants to be useful to form Hquid crystals exist when the cross-sectional areas of the polar group and the hydrocarbon chain are similar. This means that double-chain surfactants are eminently suited, and lecithin (qv) is a natural choice. Combiaations of a monochain ionic surfactant with a long-chain carboxyHc acid or alcohol yield lamellar Hquid crystals at low concentrations, but suffer the disadvantage of the alcohol being too soluble ia the oil phase. A combination of long-chain carboxyHc acid plus an amine of equal chain length suffers less from this problem because of extensive ionisa tion of both amphiphiles. 

The electrostatic and steric effects can be combined to stabilize nanoparticles in solution. This type of stabilization is generally provided by means of ionic surfactants such as alkylammonium cations (Scheme 9.3). These compounds bear both a polar head group which is able to generate an electrical double layer, and a lipophilic side chain which is able to provide steric repulsion [14, 15]. 

Derivatives of acyclic olefins can be used as chain transfer agents in these polymerizations. The most effective are those with a terminal double bond. For example, in the ROMP of 248 catalysed by [Ru(H20)6](0Ts)2 the transfer constant (klr/kp) for CH2=CHCH2CH20H is 0.21. The size of the polymer particles produced by emulsion polymerization of 248, using RUCI3 with a non-ionic surfactant, is of the order of 0.03 /zm577. 

The characteristic effect of surfactants is their ability to adsorb onto surfaces and to modify the surface properties. Both at gas/liquid and at liquid/liquid interfaces, this leads to a reduction of the surface tension and the interfacial tension, respectively. Generally, nonionic surfactants have a lower surface tension than ionic surfactants for the same alkyl chain length and concentration. The reason for this is the repulsive interaction of ionic surfactants within the charged adsorption layer which leads to a lower surface coverage than for the non-ionic surfactants. In detergent formulations, this repulsive interaction can be reduced by the presence of electrolytes which compress the electrical double layer and therefore increase the adsorption density of the anionic surfactants. Beyond a certain concentration, termed the critical micelle concentration (cmc), the formation of thermodynamically stable micellar aggregates can be observed in the bulk phase. These micelles are thermodynamically stable and in equilibrium with the monomers in the solution. They are characteristic of the ability of surfactants to solubilise hydrophobic substances. 

Additional polar groups, 0=0 double bonds, and chain branching tend to increase the CMC, but changes in the hydrophilic part of the amphiphile have insignificant effects on the CMC. The addition of strong electrolytes reduces the CMC of ionic surfactants but only slightly alters that of non-ionic surfactants. Non-polar solutes may also influence the CMC of all types of surfactants. Ohanges in the CMC as a function of 10... 

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