Micelles coacervates

In our opinion these examples demonstrate the value of our way of looking at the problem. Emphasis must finally be laid on one thing. In spite of the fact that we consider the phenomena in soap solutions throughout as equilibrium phenomena, we use terms as micelle , coacervate, and so on, which on account of their colloid chemical past call forth ideas of strictly determined boundary surfaces (Freundlich s Kapillarchemie). We wish however to retain these terms without crediting the boundary surface of micelle-equilibrium liquid with a separate significance. We thus look upon a micelle in a soap solution as a formation which is in equilibrium with the rest of the solution but which through its large dimensions and its structure has properties which the soap molecule as such does not possess. It is only with this restriction that we wish to continue to speak of micelles, coacervates, etc. 

Wang, Y., K. Kimura, P. L. Dubin, and W. Jaeger (2000). Polyelectrolyte-micelle coacervation Effects of micelle surface charge density, polymer molecular weight, and poljmer/surfactant ratio. Macromolecules 33(9) 3324-3331. 

After more than 20 years, Walde et al. (1994) returned in a way to coacervate experiments, although using other methods. Walde (from the Luisi group) repeated nucleotide polymerisation of ADP to give polyadenylic acid, catalysed by polynucleotide phosphorylase (PNPase). But instead of Oparin s coacervates, the Zurich group used micelles and self-forming vesicles. They were able to demonstrate that enzyme-catalysed reactions can take place in these molecular structures, which can thus serve as protocell models. Two different supramolecular systems were used ... 

The cloud point of a mixture of nonionic surfactants is intermediate between the pure nonionic surfactants involved (95.99) The cloud point of a dilute nonionic surfactant solution increases upon addition of ionic surfactant (95.98—104). The coacervate phase forms because of attractive forces between the micelles in solution. The incorporation of ionic surfactant into the nonionic micelles introduces electrostatic repulsion between micelles, causing coacervate phase formation to be hindered, raising the cloud point. 

The equilibrium in these systems above the cloud point then involves monomer-micelle equilibrium in the dilute phase and monomer in the dilute phase in equilibrium with the coacervate phase. Prediction o-f the distribution of surfactant component between phases involves modeling of both of these equilibrium processes (98). It should be kept in mind that the region under discussion here involves only a small fraction of the total phase space in the nonionic surfactant—water system (105). Other compositions may involve more than two equilibrium phases, liquid crystals, or other structures. As the temperature or surfactant composition or concentration is varied, these regions may be encroached upon, something that the surfactant technologist must be wary of when working with nonionic surfactant systems. 

This brief review has attempted to discuss some of the important phenomena in which surfactant mixtures can be involved. Mechanistic aspects of surfactant interactions and some mathematical models to describe the processes have been outlined. The application of these principles to practical problems has been considered. For example, enhancement of solubilization or surface tension depression using mixtures has been discussed. However, in many cases, the various processes in which surfactants interact generally cannot be considered by themselves, because they occur simultaneously. The surfactant technologist can use this to advantage to accomplish certain objectives. For example, the enhancement of mixed micelle formation can lead to a reduced tendency for surfactant precipitation, reduced adsorption, and a reduced tendency for coacervate formation. The solution to a particular practical problem involving surfactants is rarely obvious because often the surfactants are involved in multiple steps in a process and optimization of a number of simultaneous properties may be involved. An example of this is detergency, where adsorption, solubilization, foaming, emulsion formation, and other phenomena are all important. In enhanced oil recovery. 

As the temperature of a mixed surfactant system is increased above its cloud point, the coacervate (concentrated) phase may go from a concentrated micellar solution mixed ionic/nonionic systems, it would be of interest to measure thermodynamic properties of mixing in this coacervate as this temperature increased to see if the changes from micelle to concentrated coacervate were continuous or if discontinuities occurred at certain temperatures/compositions. The similarities and differences between the micelle and coacervate could be made clearer by such an experiment. 

Stuart, M.A.C., Besseling, N.A.M. and Fokkink, R.G. (1998) Formation of micelles with complex coacervate cores. Langmuir, 14, 6846-6849. 

Micelles and Pseudocells. The characteristics and properties of coacervate drops have suggested to us the possibility of using them as "pseudocells" to uniquely restructure foods. Our concept is that coacervate "pseudocells" may be built up into simulated tissue systems through interaction between coacervate drops. 

Formation and Structure of Middle Phase Microemulsion. The 1 - m - u transitions of the microemulsion phase as a function of various parameters are shown in Figure 4. Chan and Shah (31) compared the phenomenon of the formation of middle phase microemulsion with that of the coacervation of micelles from the aqueous phase. They concluded that the repulsive forces between the micelles decreases due to the neutralization of surface charge of micelles by counterions. The reduction in repulsive forces enhances the aggregation of micelles as the attractive forces between the micelles become predominant. This theory was verified by measuring the surface charge density of the equilibrated oil droplets in the middle phase (9). 

As a rule, the combination of high protein surface charge density, high polymer linear charge density of opposite sign, and low ionic strength promotes precipitation rather than coacervation. The similitude with ionic micelle/... 

S. Priyanto, G.A. Mansoori, A. Suwono, Measurement of property relationships of nano-structure micelles and coacervates of asphaltene in a pure solvent . Chemical Engineering Science, 56, 6933-6939, (2001). 

Oparin and coworkers [125,126] have studied the enzymic polymerization of ADP by polynucleotide phosphorylase (PNPase) and Mg ions in coacervates in an attempt to construct primitive forms of precellular structures. Walde et al. [127] have investigated this enzymic ADP polymerization in AOT reversed micellar solutions instead of coacervates. The PNPase-catalyzed synthesis of poly(A) (polyadenylic acid) in the AOT reversed micelles was carried out by mixing two reversed micellar solutions, one containing ADP and the other containing the enzyme. 

Lastly, we have determined that in addition to polymer structure, the addition order of materials, such as polymer, surfactant and salt, to a formulation affects the compositional range of coacervate formation and the coacervation mechanism. Depending on the flexibility of the polymer structure, the mechanisms of coacervation in the presence of added electrolyte can vary. Poly (4-vinyl pyridine)-LAS-NaCl systems show a polymer collapse mechanism with the formation of a super-salt when salt and polymer are pre-mbced. However, for the stiff cellulosic polymers, the pre-mixing of salt and polymer before surfactant addition enhances micelle-bridging without complete polymer collapse. Also, the addition... 

Zhou H, Sun X, Zhang L, Zhang P, Li J, Liu Y-N. Fabrication of biopoly meric complex coacervation core micelles for efficient tea polyphenol delivery via a green process. Langmuir. 2012 28(41) 14553-14561. 

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