Hydrogels Are Unions Of Polymeric Solid Materials

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Hydrogels are unions of polymeric solid materials

Introduction

Hydrogels are unions of polymeric solid materials with long chains that are cross -linked, forming three -dimensional networks. Mainly, they are formed by potassium acrylate and are commonly known because when they get in touch with a solvent, such as water, they absorb and swell it, so that they produce an important conformational change and become much more elasticand soft.

Developing

The fact that its components have long chains is beneficial for the formation of the hydrogel, since it makes it much more flexible, allowing it to be challenged and deform, allowing the entry of the solvent molecules inside. The number of possible applications that can be carried out with hydrogels are multiple, among which we highlight the water and nutrient supply in plants and soils and medical purposes.

Characteristic

The main characteristics of hydrogels are:

• Hydrophilic character: contain groups such as alcohols or carboxyl groups.
• Solubility: insoluble in water due to the three -dimensional polymeric network they have.
• Consistency: they are soft and elastic, since they contain a hydrophilic monomer and its polymer cross -rise density is low.
• Ability to swell: for this reason, they increase their volume considerably until they reach a chemical-physical balance when joining a solvent. When he is not hydrated, Xerogel is considered.
• Molecular weight: it affects investing the diffusion constant of the solutes, that is, if the molecular weight decreases, the constant increases.
• PKA (ionization percentage): In general, the hydrogel behavior will depend on this. That is, in case it is anionic, in general, it swells more when the external pH is greater than its pka. On the other hand, the cationic swell more when the pH is lower.

Classification

There are multiple ways to classify hydrogels according to the characteristics we are attended to for it. Mainly, they are divided into two groups according to the nature of union of the compounds that form them:

• Physical hydrogels: they join by non -covalent links (van der waals) and result in non -cross -linked networks.
• Chemical hydrogels: they join through stronger links, so, in case of break, the disintegration of the gel occurs. In this case, cross -linked networks are formed.

In addition to these, there are other classification methods among which we will highlight:

1. According to the type of lateral groups: neutral or ionic.
2. According to mechanical and structural properties: related or ghost networks.
3. According to how they are obtained: Homopolimeric, copolymeric, multipolimer or polymeric network interpenetrated.
4. According to the Hydrogel structure: amorphous, semicrystalline, formed by hydrogen unions and hydrocoloidal aggregates.
5. According to other behaviors: hydrogels that produce conformational change depending on the external environment, that is, physiologically sensitive hydrogels (dependent on pH, temperature, ionic force and electromagnetic radiation).

Chemical structure

As we have mentioned earlier, a hydrogel is a network formed by different polymorphic compounds that are very absorbent and that, when joining a solvent, produce a conformational change by which they become very flexible. In addition, when swelling, its volume is significantly increasing, but the shape is always maintained until it reaches a physicochemical balance. Until the moment in which the interaction occurs, they remain in a dehydrated (XeroGel) and its structure is much more compact.

The links that facilitate the union of polymorphic solids are mainly covalent bonds, although hydrogen bonds and those of Van der Vaals also appear. Electrostatic forces (attraction and repulsion), hydrophobic unions and ionic interactions stand out. At the chemical level, hydrogels are characterized by the presence of groups such as alcohols or carboxils and, on the other hand, of hydrophobic groups.

Synthesis

The formation of a hydrogel is carried out from certain components that are necessary to carry out polymerization:

• Initiator. Responsible for producing free radicals that will be used for reaction. The most typical systems are: free, ionic radicals, gamma radiation, redox ..
• Cross -ruler. Whereby the reticulated three -dimensional structure is achieved. This generates covalent unions in the mesh or three -dimensional network which makes the hydrogel insoluble

Solvent

Monomer. We distinguish three types mainly:

1. With non -ionizable side chains (acrylamide among others).
2. With ionizable side chains (acids, acrylic or sulfonic)
3. Zwiterionic (with two groups loaded and attached to the main chain).

conclusion

To synthesize an outrageous hydrogel, we can do it in different ways. On the one hand, by radiation, where emissions of electrons, X -rays or gamma, ultraviolet light can be used … that will excite the polymer and form the desired structure. On the other hand, it can also be achieved through a chemical reaction consisting of a polymerization and cross -linking between one or more monomers and a multifunctional monomer. 

There are various techniques through which he obtained in covalent crossbar, highlights:

• Polymerize a solution containing acrylic acid, inducing that self-entent is eliminated because hydrogen from the compound skeleton is eliminated and therefore, different radicals are combined.
• Ionizing radiation.
• Copolimerization of different monomers with the aim of having the desired properties. Normally, one of the monomers is hydrophobic and the other hydrophilic.