Polyelectrolyte complex temperature

A variety of synthetic polymers, including polycarbonate resins, substituted olefins, and polyelectrolyte complexes, are employed as ultrafiltration membranes. Many of these membranes can be handled dry, have superior organic solvent resistance, and are less sensitive to temperature and pH than cellulose acetate, which is widely used in RO systems. 

Polyelectrolyte complexes composed of various weight ratios of chitosan and hyaluronic acid were found to swell rapidly, reaching equilibrium within 30 min, and exhibited relatively high swelling ratios of 250-325% at room temperature. The swelling ratio increased when the pH of the buffer was below pH 6, as a result of the dissociation of the ionic bonds, and with increments of temperature. Therefore, the swelling ratios of the films were pH-and temperature-dependent. The amount of free water in the complex films increased with increasing chitosan content up to 64% free water, with an additional bound-water content of over 12% [29]. 

For the preparation of spray-dried polyelectrolyte complexes, the polyanion was dissolved in dilute NH4HCO3 solution and mixed with the chitosan carbamate solution just before spray-drying. The excess NH4HCO3 decomposed thermally between 60 and 107 °C on the other hand, the carbamate function released carbon dioxide under the effect of the temperature at which the spray-drier was operated, thus regenerating chitosan at the moment of the polyelectrolyte microsphere formation (Fig. 5). 

Polyelectrolyte complexes can be prepared in a desired range of mass, size and structure density. The behavior of the PECs can be controlled by external parameters such as the ionic strength, the pH of the medium or the temperature. Therefore, such complexes should be of great interest as potential carrier systems for drugs, enzymes, or DNA because charged species can easily be integrated into the complex particles. 

The formation of polyelectrolyte complexes (PEC) is governed by the characteristics of the individual polyelectrolyte components (e.g. properties of ionic sites - strong or weak electrolyte -, position of ionic sites, charge density, rigidity of macromolecular chains) and the chemical environment (e.g. solvent, ionic strength, pH and temperature). Polyelectrolyte complexes are either separated from the solution as solids or liquids or they are still soluble in solution or may settle as gels due to variation of the controlling factors mentioned above. 

Up to now, the effects of the characteristics of the polyelectrolyte components themselves have been discussed. The effect of the reaction conditions, for example ionic strength, solvent, concentration and temperature on the formation of polyelectrolyte complexes will also be discussed in detail. When increasing the ionic strength, the following phenomena are expected to be observed ... 

Fig. 16 a, b. Effect of temperature and solvent on the formation of the polyelectrolyte complexes of poly(methacrylic acid) (PMAA)-poly-(4-vinylbenzyltrimethy]ammonium chloride) (PVBMA) (a) In water, (b) in methanol... 

When oppositely charged polyelectrolytes with a relatively low-charge density are mixed at an appropriate temperature and pH concentration, a liqnid polyelectrolyte complex called complex coacervate is formed. This techniqne is widely nsed in the preparation of polymeric particles. 

In a PEC used to deliver a protein, the latter is often used as one of the polyelectrolyte components of the complex. Examples of PECs in which one of the two polyelectrolyte components is an active substance itself, are complexes of chitosan and insulin. The PEC composed of trimethyl chitosan (TMC) and pegylated TMC (PEG-g-TMC) can be obtained simply by mixing the solutions of TMC and insulin at various mass and charge ratios. These PECs were stable in simulated intestinal fluid at pH 6.8. However, they disintegrated in simulated gastrointestinal fluid at pH 1.2. The PECs also protected insulin from temperature-induced denaturation up to 50 °C and from degradation by trypsin. Based on these results, the authors suggested that polyelectrolyte complexation can be a useful technique for fabrication of insulin delivery systems for oral administration. 

Yoshizawa T, Shin-ya Y, Hong KJ (2005) pH- and temperature-sensitive release behaviors from polyelectrolyte complex films composed of chitosan and PAOMA copolymer. Eur J Pharm Biopharm 59 307-313... 

Keeping the microcapsules at raised temperature can lead to the change in their size. (PSS/PDADMAC)5 microcapsules obtained on the basis of melamine formaldehyde particles increased in diameter from 5.5 up to 7.5 micrometers at heating (40°C, 2 hours). Possible reasons of such behavior are supposed to be connected with reorganization of the polyelectrolyte shell structure caused by the change of ionic contact number in a polyelectrolyte complex under the temperature influence. The loosening of the shells leads to the change of its extension, and the diameter of a microcapsule. 

Dautzenberg H, Gao Y, Hahn M (2000) Formation, structure, and temperature behavim of polyelectrolyte complexes between ionically modified thermosensitive polymers. Langmuir 16 9070-9081... 

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