Swelling polyelectrolytes

The antibacterial water-absorption sheet described in the foregoing is a side or end-sealed superabsorbent polymer layer or powdery inorganic antibacterial agent mixed layer. Thus, it is somewhat disadvantageous in terms of manufacturing process, cost, and ease of use. As an improved type, the absorption polymer sodium poly(acrylic acid) is replaced by a pulp-sheet-type swelling material, a metallic salt of fibrous carboxymethyl cellulose. A swelling polyelectrolyte made of the same polymer but part of the polymer is a cationic water-soluble polymer, such as polyamine, that can also be used. A water-absorption sheet as shown in Fig. 1 is proposed. 

Approximately a minimum of 1 to 5,000 is required before complexation is no longer dependent on molecular weight for small anions such as KI and l-ariiLinonaphthaLine-8-sulfonate (ANS) (86,87). The latter anion is a fluorescent probe that, when bound in hydrophobic environments, will display increased fluorescence and, as expected, shows this effect in the presence of aqueous PVP. PVP, when complexed with Hl, shrinks in si2e as it loses hydrodynamic volume, possibly because of interchain complexation. ANS, on the other hand, causes the polymer to swell by charge repulsion because it behaves like a typical polyelectrolyte (88). 

A similar example is the formation of nonstoichiometric interpolymeric complexes between mutually complementary polyelectrolytes — polycation and polyanion [69,70], They behave like true polymer networks and are capable of swelling the interpolymeric complexes between PAAc and polyethylene piperazine swells, for instance, 16-18 times [70], Also advantageous in this case is the possibility to carry out this type of crosslinking in open systems, such as soil. 

In most cases, the swelling of polyelectrolyte hydrogels depends only on ionic strength of the solution but not on the size and nature of the ions [101]. Therefore, the ionic suppression curves similar to those of Fig. 2 and 3 are to some extent universal and allow to predict quantitatively the swelling of hydrogels for practically any ionic situation. 

In contrast to polyelectrolyte hydrogels, nonionic ones are almost insensitive to the ionic composition of the medium. In particular, the equilibrium swelling degree of a charge-free PAAm gel practically does not depend on the Cu2 + concentration (Fig. 4, curve 0) nor on the concentration of several other ions or on the pH value [101]. 

The swelling pressure of polyelectrolyte gels is usually considered as a sum of the network (jtnct) and ionic contributions (nion) [4, 99, 101, 113, 114]. The former describes the uncharged gel while taking into account the interaction between the polymer segments and the solvent as well as the network elasticity [4] ... 

The effect of the network density on the polyelectrolyte hydrogel elasticity can be understood taking into account the fact that the elastic modulus is closely connected with the swelling pressure (see, for example, Refs. [20, 115]) ... 

In the following paper, the possibility of equilibration of the primarily adsorbed portions of polymer was analyzed [20]. The surface coupling constant (k0) was introduced to characterize the polymer-surface interaction. The constant k0 includes an electrostatic interaction term, thus being k0 > 1 for polyelectrolytes and k0 1 for neutral polymers. It was found that, theoretically, the adsorption characteristics do not depend on the equilibration processes for k0 > 1. In contrast, for neutral polymers (k0 < 1), the difference between the equilibrium and non-equilibrium modes could be considerable. As more polymer is adsorbed, excluded-volume effects will swell out the loops of the adsorbate, so that the mutual reorientation of the polymer chains occurs. 

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]. 

A simple example of gel formation is provided by chitosan tripolyphosphate and chitosan polyphosphate gel beads the pH-responsive swelling abihty, drug-release characteristics, and morphology of the gel bead depend on polyelectrolyte complexation mechanism and the molecular weight. The chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution by ionotropic cross-hnking or interpolymer complexation, respectively. 

Siegel, R, A, Hydrophobic Weak Polyelectrolyte Gels Studies of Swelling, Equilibria and Kinetics. Vol. L 09, pp. 233-268. 

The equation for the equilibrium swelling degree is more complicated for polyelectrolyte gels—those with ionizable groups—because of the need to include the additional ion-related terms in Eq. (5). The nion term can be substantial... 

Figure 3 Equilibrium swelling degree of polyelectrolyte gels as predicted by Eq. (12).

J Hasa, M Ilavsky, K Dusek. Deformational, swelling, and potentiometric titration of polyelectrolytes. J Polym Sci Polym Phys Ed 13 253-262, 1975. 

RA Siegel. Hydrophobic weak polyelectrolyte gels—Studies of swelling equilibria and kinetics. Adv Polym Sci 109 233-267, 1993. 

Counterion gel 4- —> swelling 4- (Exception polyelectrolyte complexes) Effect depends on species salting-in/salting-... 

Oppermann, W., Swelling Behavior and Elastic Properties of Ionic Hydrogels, in Polyelectrolyte Gels Properties, Preparation, and Applications (R. S. Harland and R. K. Prud homme Eds.), pp. 159-170. American Chemical Society, Washington (1992). 

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