**6. Types of porous structure obtained**

Another attractive feature is the development of new complex hydrogel films with targeted architecture. Porous materials are materials having different pore size structures (from nanometer to millimeter). Hydrogel has a porous structure in size of the micrometer called superporous structure. **Figure 11** shows the pores with different shapes with different accessibility. Almost, the surfaces of pores are hydrophilic, and the void begins to open due to group's repletion of the same charge. The swelling process shows variability of pore structure obtained as (a) closed pores, (b) one side opened pores like cylinder, (c) two sides opened pores like tunnel, (d) one side opened pores like ink bottle shaped, (e) two side opened pores like funnel shaped, (f) pores with rough surface, (g) separated closed pores, (h) interconnected pores, (k) collected pores or density pores, and (p) pores like internal tunnel. In maximum swelling we reach to superporous hydrogel when the pores predominate than the solid network.

**7. Factors affecting superabsorbent hydrogel**

**Figure 12.** SEM images of (a) the α-elastin hydrogel fabricated at 60 bar CO<sup>2</sup>

Comparison of SEM images (b) of α-elastin hydrogel produced under atmospheric CO<sup>2</sup>

increased the pore size of the fabricated hydrogels [53].

Increasing the ratio of cross-linked portion leads to slow down the movement of chains, resulting in the decrease in free volume, the pore sizes, and the swelling degree which are also decreasing. This can be observed by SEM analysis or DSC where increased cross-linking

The ionization power and number of hydrophilic functional groups along the hydrogel chains and its counterion type play an important role in the degree of swelling. A high proportion of superabsorbent hydrogels are present as acrylates with carboxylic acid functional groups, which in the salt form undergo dissociation upon contact with water. In the dissociated state, the hydrogel network will have a series of functional groups that have the same electric charge and thus repel each other. This leads to expansion of the hydrogel network structure with the further absorption of water molecules. Furthermore, the number of hydrophilic moi-

According to the required application, the hydrogels have been tailored and designed to achieve the purpose of applications. The presented section demonstrates the research concerning the characterization of hydrogels on various bases, physical and concoction qualities

) of the polymer [54, 55]. However, in some cases, a

[56].

, where nonfreezing (bounded) water mol-

pressure which was highly porous structure.

http://dx.doi.org/10.5772/intechopen.74698

conditions (1 bar) indicated that

Superabsorbent

57

**7.1. Density of cross-linking**

a high-pressure CO<sup>2</sup>

causes increase of glassy temperature (*Tg*

decreased cross-linking leads to a decrease of *Tg*

**7.3. Applications of superabsorbent hydrogel**

of these items, and specialized practicality of their usage.

ecules are attached to function groups causing a decrease of *Tg*

**7.2. The ratio of hydrophobic/hydrophilic surface area of the hydrogels**

eties when increasing the swelling could be increased and vice versa.

Further compression properties of the superporous hydrogel are α-elastin fabricated under 60 bar CO<sup>2</sup> pressure which was comparable with 1 bar. SEM image in **Figure 12** shows the pore size of the hydrogels which was enhanced 20-fold when the pressure was increased from 1 to 60 bar.

**Figure 11.** Given the different type of pores where white region is hydrophilic region filled with water and blue region is hydrophobic region or covalent bond of cross-linkage. **Shape**: a, k, g, and h (closed pores: (b) cylindrical open shaped, (c and p) tunnel shaped, (d) ink bottle shaped, (e) funnel shaped, and (f) roughness). **Accessibility**: a, p, h, g, and k (closed pores: c, e, d, f, and p).

**Figure 12.** SEM images of (a) the α-elastin hydrogel fabricated at 60 bar CO<sup>2</sup> pressure which was highly porous structure. Comparison of SEM images (b) of α-elastin hydrogel produced under atmospheric CO<sup>2</sup> conditions (1 bar) indicated that a high-pressure CO<sup>2</sup> increased the pore size of the fabricated hydrogels [53].
