Coacervates phenomena

The complicated coacervation phenomena occurring within the plane of the triangle at mixing ratios in the neighbourhood of the reversal of charge line will be further discussed in Chapter X 2t (p.378). 

The absence of flocculation or coacervation phenomena in a mixture of oppositely charged colloids does not necessarily mean that colloid-colloid interaction is lacking. In mixtures of gum arabic and gelatin at lower pH values (e.g., pH 1.73 — 2.3) no coacervation occurs. Still interaction is present, for in Fig. 43 (p. 324) the curve continues its normal course in this pH range, absolutely different from that in Fig. 50 (p. 332), where the curve ends vertically at 100 % N. Thus in the sol mixture soluble combinations of gelatin and gum arabic are present and they are preferentially absorbed on the carborundum particles, which were used to measure the reversal of charge in these clear sol mixtures. 

The points c and d and point r on the side -A / of the triangle have the same significance for the binary isohydric series of mixtures of I with A. We may then expect that the coacervation phenomena in mixtures of the three colloids can be appreciated when the course of three curves is known, namely the curve which connects a with c, the curve which connects the two reversal of charge points r and the curve which connects b and d. 

The initial polymer-surfactant-salt interaction studies prompted a question of the effect of addition order on the coacervation mechanism. If the salt is added first into a polymer environment will the coacervation phenomenon be the same as a system where surfactant and electrolyte are first introduced This question was addressed by investigating the effect of addition order in the presence of salt for both the synthetic and cellulosic polymer systems. The methods used for each system are discussed in the Experimental section and the addition orders are outlined in Table II. 

Coa.cerva.tlon, A phenomenon associated with coUoids wherein dispersed particles separate from solution to form a second Hquid phase is termed coacervation. Gelatin solutions form coacervates with the addition of salt such as sodium sulfate [7757-82-6] especially at pH below the isoionic point. In addition, gelatin solutions coacervate with solutions of oppositely charged polymers or macromolecules such as acacia. This property is useful for microencapsulation and photographic apphcations (56—61). 

Coacervation occurs in tropoelastin solutions and is a precursor event in the assembly of elastin nanofibrils [42]. This phenomenon is thought to be mainly due to the interaction between hydro-phobic domains of tropoelastin. In scanning electron microscopy (SEM) picmres, nanofibril stmc-tures are visible in coacervate solutions of elastin-based peptides [37,43]. Indeed, Wright et al. [44] describe the self-association characteristics of multidomain proteins containing near-identical peptide repeat motifs. They suggest that this form of self-assembly occurs via specific intermolecular association, based on the repetition of identical or near-identical amino acid sequences. This specificity is consistent with the principle that ordered molecular assembhes are usually more stable than disordered ones, and with the idea that native-like interactions may be generally more favorable than nonnative ones in protein aggregates. 

In the coacervation process, the core substance is first added to a homogeneous solution of the selected solvent and polymer. Mechanical agitation is used to disperse the immiscible core to create tiny droplets suspended in solution (i.e., an emulsion). The coacervation or phase separation phenomenon is then induced by several means, such as changing the temperature and/or acidity of the polymer solution or adding salts, nonsolvents, or incompatible (immiscible) polymers to... 

The electrostatic interaction between oppositely charged protein and polysaccharide can be utilized for encapsulation and delivery of hydro-phobic nutraceuticals. As a result of this interaction, we may have either complex coacervation (and precipitation) or soluble complex formation, depending on various factors, such as the type of polysaccharide used (anionic/cationic), the solution pH, the ionic strength, and the ratio of polysaccharide to protein (see sections 2.1, 2.2 and 2.5 in chapter seven for more details) (Schmitt et al, 1998 de Kruif et al., 2004 Livney, 2008 McClements et al, 2008, 2009). The phenomenon of complex... 

The Phenomenon of Segregative Phase Separation — Simple Coacervation ... 

The phenomenon was called simple coacervation by Bungenberg de Jong (1949) in order to distinguish it from complex coacervation where both polymers are concentrated in the same solvent-depleted phase. The phenomenon of simple coacervation in aqueous food biopolymer systems has attracted considerable interest for many years. This is because of the perception of the potential of these phase-separated biopolymer... 

Theoretical treatments of simple coacervation based on the statistical thermodynamics of polymer solutions have been set out by Scott (1949), Tanford (1961), Zeman and Patterson (1972), and Hsu and Prausnitz (1974). These treatments have shown that the main molecular factors affecting the phenomenon are ... 

Coacervation Is a very complicated physical phenomenon. And, many factors affect the properties of the resulting microcapsules. Coacervation and phase separation from organic and aqueous media Involve many properties, materials and processes such as phase Inducing agents, stirring rates, core to wall ratios, polymer characteristics, core characteristics (wettability, solubility), cooling rates and rates of addition. 

There yet remains considerable amounts of art to coacervative microencapsulation. Here art is best described as a phenomenon awaiting a scientific explanation. In coacervation the kind of addition and the rate of and order of addition are extremely critical. In general, the slower the process the better it is for coacervative encapsulation. It is the intuitive feel that encapsulators practice that it frequently termed "art. ... 

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... 

Extractions Based on the Phase Separation Behavior of Aqueous Micellar Solutions. The extraction and concentration of components in an aqueous mixture can sometimes be effected via use of appropriate surfactant systems that are capable of undergoing a phase separation as a result of altered conditions (i.e. temperature or pressure changes, added salts or other species, etc.). Two general types of such surfactant extraction systems will be described (i) those based on the cloud point phenomenon and (ii) those based on coacervation formation. 

Complex coacervation of globular proteins with the strong polycation PDMDAAC appears to be a purely coulombic phenomenon, controlled by ionic strength and protein net charge (via pH). Turbidimetric pH titrations suggest that the process resembles a critical phenomenon since solutions go from optical clarity to high turbidity over a pH interval of 0.3 units or less. 

In this contribution, we discuss coacervation as a phenomenon between one or two polymers in a... 

It is interesting to observe that rod-shaped molecules such as tobacco mosaic virus or flat plate particles such as bentonite show the so-called coacervation at rather low concentrations at which the second phase solution shows a spontaneous birefringence. Oparin discussed the possible connection of such a phenomenon with the origin of life (25). 

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). 

This phenomenon is known for surfactant liquid crystals, where the macroscopic shape can be induced by external forces. Thus, if an external orienting force is exerted on the crystallite coacervates and a sufficient time is allowed for the crystallization to be completed, a maCTOscopic homogeneous crystal may form. Otherwise, even the primary particles are expected to be heterogeneous. 

Complex coacervation is a phenomenon by which an aqueous solution of oppositely charged polyelectrolytes separates into two distinct phases. The more dense phase is called the complex coacervate or coacervate. It is a relatively concentrated polyelectrolyte solution. The second phase, a relatively dilute polyelectrolyte solution, is called the equiibrium liquid. The difference in concentration of the coacervate and equilibrium liquid phases is determined by the intensity of the coacervation interaction. The more intense this interaction is, the greater the concentration difference. ... 

The formation of lyophilic colloidal systems may also take place via phase separation of polymer solutions. A typical phenomenon that occurs upon phase separation is the formation of the so-called coacervates, which are characteristic nuclei containing higher concentration of polymer, as compared to that in the medium surrounding them. It is speculated that coacervation was a second stage (after the formation of adsorption layers) in the ordered structuring of organic matter on Earth. 

Phase separation process takes advantage of the phenomenon called polymer- lymer incompatibility. The process utilizes two polymers that are soluble in a common solvent yet do not mix with one another in the solution. The polymers form two separate phases one polymer intended to form the capsnle walls, the other incompatible polymer meant to induce the separation of the two phases, but not meant to be part of the capsule wall material. This process is somewhat related to the complex coacervation process. The phase separation process is considered as the oldest true encapsulation technology first developed by the National Cash Register Company for carbonless copy-paper. Microencapsnlation by coacervation involves the phase separation of one or more hydrocolloids from the initial solntion, and the subseqnent deposition of the newly formed coacervate phase around the active ingredient suspended or mnulsified in the same reaction media. The size of the miCTocapsules formed may be in the range of 10-250 pm. 

Simple coacervation can also be induced by adding an inorganic salt for polymer desolvation, and the phenomenon is sometimes called salting-out. " The ability of inorganic cations to indnce coacervation is expressed by the Hofmeister or lyotropic series, which arranges ions in the order of decreasing salting out capacity for the polymers ... 

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