Coacervation simple

Xylan-based micro- and nanoparticles have been produced by simple coacervation (Garcia et al., 2001). In the study, sodium hydroxide and chloride acid or acetic acid were used as solvent and non-solvent, respectively. Also, xylan and surfactant concentrations and the molar ratio between sodium hydroxide and chloride acid were observed as parameters for the formation of micro- and nanoparticles by the simple coacervation technique (Garcia et al., 2001). Different xylan concentrations allowed the formation of micro- and nanoparticles. More precisely, microparticles were found for higher concentrations of xylan while nanopartides were produced for lower concentrations of the polymer solution. When the molar ratio between sodium hydroxide and chloride acid was greater than 1 1, the partides settled more rapidly at pH=7.0. Regarding the surfactant variations, an optimal concentration was found however, at higher ones a supernatant layer was observed after 30 days (Garda et al., 2001). 

Gelatin and albumin nanoparticles have been prepared through desolvation of the dissolved macromolecules by either salts (e.g., sodium sulfate or ammonium sulfate) or ethanol [179-182], This is, in principle, similar to a simple coacervation method. The particles can then be insolubilized through cross-linking with an optimum amount of aldehydes. These phase separation methods avoid the use of oils as the external phase. 

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 ... 

Gupta, A., Bohidar, H.B. (2005). Kinetics of phase separation in systems exhibiting simple coacervation. Physical Review E, 72, 011507. 

Mohanty, B., Bohidar, H.B. (2003). Systematic of alcohol-induced simple coacervation in aqueous gelatin solutions. Biomacromolecules, 4, 1080-1086. 

Simple coacervation involves the use of either a second more-water soluble polymer or an aqueous non-solvent for the gelatin. This produces the partial dehydration/desolvation of the gelatin molecules at a temperature above the gelling point. This results in the separation of a liquid gelatin-rich phase in assocation with an equilibrium liquid (gelatin-poor) which under optimum separation conditions can be almost completely devoid of gelatin. 

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. 

We synthesized [13] IPNs composed of polyethylene oxide) (PEO) (polymer A) and poly(N-acryloylpyrrolidine) (PAPy) (polymer B). The IPN was synthesized by simultaneous crosslinked polymerization of APy and PEO. The overall reaction scheme for IPN synthesis by radical polymerization for APy (polymer A) and addition polymerization for PEO (polymer B) is shown in Fig. 3. This pair shows simple coacervation behavior in water. The IPN is constructed from PEO and PAPy networks as shown in Fig. 4. Chemically independent networks of polymer A and polymer B are interlocked and macroscopic phase separation in water swollen states is avoided. 

Coacervation is the separation into two liquid phases of a ternary dispersion, each phase containing a preponderance of one solute and a minor concentration of the other, and vice versa each phase is a coacervate. The event is simple coacervation if the cosolutes have identical charge it is complex coacervation if the cosolutes are oppositely charged (Jirgensons and Strau-manis, 1962). Either phase may develop a network independently of the other (Moritaka el al., 1980), or one phase may be suspended as droplets in the other. Alternatively, one solvent-depleted phase may contain the two cosolutes, while the other phase is preponderantly solvent. 

Several researchers [163-165] have studied simple coacervation of chitosan in the production of chitosan beads. In general, chitosan is dissolved in aqueous acetic acid or formic acid. Using a compressed air nozzle, this solution is blown... 

Classification and Nomenclature. Coacervates can be divided into simple ones and complex ones based on the complexity of their chemical composition. Simple coacervates form when a compound with a great affinity for water is added to a solution of a hydrophilic molecule, causing its dehydration and a decrease in its solubility. Molecules of the same chemical composition are thus involved in simple coacervation. Complex coacervates are obtained when solutions of positively charged molecules and negatively... 

Coacervating agents (component If Non-solvents for the polymer Electrolytes ( Simple coacervation )... 

POLYMER COACERVATION INDUCED BY PARTIAL POLYMER DESOLVATION (SIMPLE COACERVATION)... 

A very frequently described family of polymers subjected to simple coacervation are cellulose derivatives, particularly ethyl cellulose (EC). ° While most cellulose ethers are soluble in water, EC and the cellulose esters are insoluble or only partly soluble in water, e.g., as a function of pH. For coacervation of EC, toluene is a preferred good solvent and cyclohexane a poor solvent. Gradual addition of cyclohexane to a solution of EC desolvates the polymer. Alternatively, EC can be dissolved in hot cyclohexane cooling to room temperature induces polymer phase separation. In both these cases, the coacervate film or droplets can be hardened by exposing the coacervate to a large volume of cyclohexane, whereby physical cross-links are formed. 

Gelatin and cellulose derivatives are probably the most widely used polymers in simple coacervation... 

For simple coacervation induced by non-solvent addition in aqueous systems, ethanol, acetone, dioxane, isopropanol, and propanol are the most preferred to cause polymer desolvation and phase separation. In organic systems, mainly non-polar solvents. 

To our knowledge, simple coacervation has essentially remained a technology described by academics and used for research rather than in pharmaceutical industry. Green first demonstrated the microencapsula-tion of oil droplets by simple coacervation of gelatin. In this study, gelatin coacervation was induced by sodium or ammonium sulfate. Since then, simple coacervation has been used to encapsulate foods, flavors, and pharmaceuticals. ... 

Simple coacervation of cellulose derivatives has been used for microencapsulation of various drugs, such as theophylline, ibuprofen, indomethacin, adryamicin, " and nicardipine. The goal of micro-encapsulating these drugs was to decrease their gastric irritation, mask the bitter taste and, very importantly, to achieve sustained release. 

Weiss, G. Knoch, A. Laicher, A Stanislaus, F. Daniels, R. Simple coacervation of hydroxypropyl methyl cellulose phthalate (HPM(7P). I. Temperature and pH dependency of coacervate formation. Int. J. Pharm. 1995,124 (1), 87-96. 

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