Mixed coacervate

Yoesting and Scamehorn (23) measured activity coefficients of all components in a mixed coacervate... 

One can in fact also have the case that a coacervate contains two colloids because each of these colloids, if present alone, forms a coacervate under the conditions of the experiment and these two coacervates are mutually miscible. Such a coacervate can be called a mixed coacervate. In 21 we shall even encounter examples in which two complex coacervates form a mixed coacervate containing three colloids (see p. 378). 

LLP-assisted local delivery of dmgs is realized via several strategies. In the first strategy, soluble LLPs are injected and their coacervation is triggered by the body temperature. Here, the dmg can be covalently attached to the ELP or it can just be mixed with the ELP. In another approach, crosslinked ELP depots containing a dmg can be produced and then implanted to generate a stable release of the dmg. 

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. 

The extent of reversibility of complexation depends mainly on the aqueous environment and the mixing conditions (Tolstoguzov, 1986 Galazka et al, 1999). The tendency towards non-equilibrium formation of an insoluble coacervate is enhanced at low ionic strength and at pH values significantly below the p/ of the protein. 

At the mixing ratio where coacervation is maximized, the protein-polysaccharide complexes are electrically neutral. 

There is evidence that random mixing of partially charge-neutralized hydrated polyelectrolyte complexes inside the coacervate phase imparts higher configurational entropy to these less stiff polyelectrolyte molecules as compared to those in the pre-coacervation phase (Kaibara et al.,... 

When two different polymer solutions are mixed, they frequently undergo one or several distinct types of interaction, which in each case can lead to phase separation at polymer concentrations above a certain critical level [12]. In one case, two solution phases of approximately equal volume are formed, consisting of polymer A- and polymer B-rich solutions, respectively. This phase separation is called incompatibility, or simple coacervation. In the second case, two phases are formed but both polymers are concentrated in one of the phases (the precipitate ) while the other phase (the supernatant ) may be essentially polymer free. This separation is called complex coacervation. The two phase separation phenomena are shown in Fig. 2. 

COACERVATION. An important equilibrium state of colloidal or macromolecular systems. It may be defined as the partial miscibility of two or more optically isotropic liquids, at least one of which is in Ihe colloidal state. For example, gum arabic shows the phenomenon of coarcrvalion when mixed with gelatin. It also may be defined as the production, hy coagulation of a hydrophilic sol, of a liquid phase, which... 

The active material in our herbicide is a liquid that does not mix with water. It can be dispersed as droplets with a mixer - in our case the droplets have to be about 0.3 mm in diameter (Figure 11-7). If you then let a polymer-rich phase form by coacervation, the polymer spontaneously wets the drop surface. It forms a liquid polymer layer around the drop. Cross-linking the polymer gives a solid capsule. 

Mixtures of oppositely charged polyelectrolytes dissolved in water can interact to form a variety of precipitates, gels, or phase-separated solutions. What is formed depends on the mixing conditions and the density of ionic charges carried by the polymer chains. Polyelectrolytes with high charge densities usually interact to form precipitates. As the charge density decreases, liquid-liquid phase separation, called complex coacervation, occurs. 

Complex coacervation is affected by pH, polyelectrolyte concentration, polyelectrolyte mixing ratio, and the neutral salt concentration. It normally occurs over a limited pH range and is suppressed by neutral salts. The optimum polyelectrolyte mixing ratio is that which neutralizes the ionic charges carried by the polyelectrolytes. The coacervation intensity is increased by dilution, which has led some researchers to suggest that complex coacervation is the mechanism by which various polymeric species are selectively isolated and concentrated in biological systems. 

Coacervation rrocedure The coacervation procedure involved weighing a 10 wt. percent gelatin solution at 55°C into a capped graduated glass centrifuge tube (15 ml capacity). The desired amount of polyphosphate solution was added as a 5 wt. percent solution. After mixing and equilibration at 55°C for 30 minutes,... 

It is postulated that this process is consistent with the dilute phase aggregate model (1) forming Type A/Type B aggregates initially when mixed at 40°C, which rearrange to form a coacervate phase when the temperature is reduced below 35°C. 

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