Swelling degree hydrogels

Aldehydes (glutaric, succinic [53-56]) are used to crosslink PVA, the network density being controlled by the ratio of aldehyde to OH-groups. The swelling degree of these hydrogels does not exceed 35-40 ml g-1, and there are almost quantitative correlations of the network density with the crosslinker concentration... 

Of particular importance for the application are the effects of the external compression and the ionic composition of the outer solution on the swelling degree. The reason is that hydrogels usually exist in mineralized aqueous solutions (soil solution) and are affected by compression, for example, produced by the surrounding particles of the soil. Even in the absence of any external load the compression develops due to the gel swelling in a constrained volume. 

Fig. 2. Dependencies of the swelling degree of PAAm hydrogels on the concentration X (in mol L-1) of H+ (/), Ca2+ (2), and Na+ (3) in the solution. Dashed curve 3 is obtained by calculation. From Dubrovskii et al. [22]...

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 equilibrium swelling degree is the most important property of a hydrogel it directly influences the rate of water sorption, the permeability to drugs, and the mechanical strength of the gel. It also affects the biocompatibility of the... 

Thus quantitative analysis of elasticity is currently elusive, despite a great deal of work ongoing in this area. The extensive literature available on rubber elasticity by and large has not been adapted to hydrogels, and further work along these lines is necessary before quantitative predictions of swelling degree can be made from independent measurable polymer properties. 

The key property of a hydrogel is its swelling degree, since this directly influences other properties such as permeability. The theoretical description of hydrogel... 

Polyivinyl alcohol) poly(acrylic acid) (PVA/PAAc) blends The swelling degree of these polyanionic hydrogels changes steeply with the change of the pH value of the measuring species it is at minimum in acids and takes its maximum in bases (Arndt et al. 1999). 

Fig. 6 Characterisation of different hydrogel materials (type A, B, C). (a) gravimetric swelling degree in PBS (b) storage modulus of the gels obtained by rheological measurements. Data are presented as mean root mean square deviation from n = 4 (a) or n = 3 (b)...

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