In Russian there are three terms that are similar to each other - gels, jellies and jellies. There is no big difference between them in structure, but these concepts are applied in different fields of activity. The term "gel" is more often used in chemistry or in relation to medicinal and cosmetic products, "jelly" - in cooking, less often in chemistry, "jelly" - in cooking and cosmetology. Let's find out what gels are and how they can be used.
The concept of "gel"
The word "gel" is of Latin origin. Gelo in translation means “freeze”, gelatus means “immobile, frozen.”
The concept is defined by colloid chemistry, the science that studies disperse systems and surface phenomena.
What is a gel in terms of chemistry? Gel is such a dispersed system with a dispersion medium in whichphase particles form a spatial structural grid. The gel contains at least two components.
Gel-colloidal system
Dispersed systems are those in which particles of one substance are uniformly distributed among particles of another substance. In such systems, they distinguish:
- dispersion medium - the substance in which distribution occurs,
- dispersed phase - a substance whose particles are distributed.
Dispersion system, for example, is fog. Here, the dispersion medium is gaseous, air plays its role, and the dispersed phase is liquid, it is water particles distributed in the air. There are many examples of disperse systems. All these systems differ in the state of aggregation of the phase and medium, as well as in the degree of fineness of the phase particles. The highest degree of phase refinement - to individual molecules - is in true solutions. Here there is no interface between the particles - the molecules of the phase and the medium. Such systems are called homogeneous, they are stable. Examples of true solutions: sulfuric acid solution, air, sea water, cast iron.
In coarse systems, the particle size is more than 100 nm, these are large particles that can be seen with the naked eye. An interface can be distinguished between the particles of the phase and the medium; therefore, such systems are called heterogeneous, they are unstable and delaminate with time. Examples of coarse systems: ground chalk in water, whitewash, mortars, toothpaste, vegetable oil in water, milk.
Particles of the phase ranging in size from 1 to 100 nm form colloidal solutions. These systems are characterized by special properties that are not characteristic of true solutions and coarse systems. Colloidal solutions are microheterogeneous rather stable systems; their particles do not settle over time under the action of gravity. Examples: aqueous colloids of metal sulfides, sulfur.
Gels are determined by the degree of dispersion of the phase to colloidal systems.
Aggregate state of phase and medium in gels
Depending on the state of aggregation of the dispersion medium and the dispersed phase, 8 types of disperse systems are distinguished. If the medium is a gas, then the phase can be a liquid (we have already considered fog) or a solid. For example, smoke or smog - particles of the solid phase are distributed in a gaseous medium. Both systems are called aerosol.
If the medium is a liquid, and solid particles of the phase are distributed in it, then such a system is called a sol or a suspension, depending on the size of the particles. Sols form gels under certain conditions.
According to the definition of chemistry, gels are dispersed systems in which the dispersion medium is a solid, the dispersed phase is a liquid. That is, gel is the name of the type of dispersion system along with emulsion, aerosol, suspension, etc.
Gels - solutions that have lost fluidity
Some solutions of macromolecular substances and sols may turn into gels during long-term storage. IUD or sol particles bind to each other, forming a continuous network. Inside such a gridsolvent particles penetrate. Thus, the dispersion medium and the dispersed phase change their roles. The phase becomes continuous, and the particles of the medium become isolated. Thus, the system loses fluidity and acquires new mechanical properties. What is a gel? These are colloidal systems that have lost fluidity due to the formation of internal structures in them.
Some gels delaminate over time, with the spontaneous release of liquid. This phenomenon is called syneresis. There is a compaction of the spatial network, a decrease in the volume of the gel, the formation of the so-called solid colloid.
The formation of a solid colloid from a gel is a common natural phenomenon. For example, the essence of blood clotting is the conversion of fibrinogen, a soluble protein, into fibrin, an insoluble protein. Under normal conditions, blood clotting is a vital process. Syneresis is important in the preparation of cottage cheese, cheese. In these cases, the phenomenon of syneresis is useful. However, this phenomenon often needs to be prevented, since it determines the shelf life and shelf life of various gels - medical, cosmetic, food. For example, marmalade and soufflé, when stored for a long time, begin to release liquid and become unusable.
The processes of converting a sol into a gel and a gel into a solid colloid are reversible. For example, the protein gelatin, which is a solid colloid, when swollen in water, turns into a jelly - gel. It is important to observe the temperature regime, bring the gelatin to a boil, but do not boil, otherwise the structure is destroyed and the gelturns into a sol, becoming fluid.
When drying, the gels are irreversibly destroyed.
Classification of gels
Depending on the chemical nature of the dispersion medium, gels are distinguished: hydrogels, alcogels, benzogels, etc. Gels that are poor in liquid or completely anhydrous are called xerogels. Xerogel is wood glue in tiles, starch, dry sheet gelatin. Complex xerogels are biscuits, flour, crackers.
Some gels contain little dry matter, but still have a three-dimensional structure. These are jelly, jelly, yogurt, soap solutions. They are called lyogels.
Select a group of coagels. These are gelatinous precipitates that are obtained by coagulating sols (silicic acid, iron (III) hydroxide, etc.) and s alting out polymer solutions. In coagels, the dispersion medium forms a separate phase, only a small part of the medium is bound.
The use and significance of gels in medical practice
Gels are used in medicine:
- when conducting ultrasound and electrographic examinations;
- to create artificial joints, ligaments;
- to stop bleeding by blockage (embolism) of blood vessels;
- for corneal restoration;
- antibacterial, antiviral gels;
- warming gels for pain relief of various parts of the musculoskeletal system;
- cooling gels for injuries.
Warming gels
Warming gelsincrease the permeability of capillaries due to the components that make up their composition - these are bee and snake venom, pepper extract; methyl salicylate has a less pronounced effect. These components cause an increase in the blood supply to the vessels - hyperemia, thus increasing local heat transfer. Warming gels are used topically for various lesions of the musculoskeletal system - joints, muscles, ligaments, tendons. They are used to relieve swelling, reduce pain, activate blood circulation in the affected area. Warming gels are used by athletes before training to prepare muscles. Muscle tissue under the action of the gel components is heated and therefore less damaged during exercise, which prevents sprains and injuries. The use of such gels after training helps relieve muscle tension and fatigue.
Popular warming gels are based on:
- pepper capsaicin or its synthetic analogue - "Finalgon", "Kapsicam";
- venom of bees and snakes - "Viprosal";
- diclofenac, ibuprofen, indomethacin - non-steroidal anti-inflammatory substances - Diclofenac, Ortofen, Indomethacin.
When using warming agents, you must read the instructions for the use of gels, take into account contraindications and observe the frequency of use.
Cooling Gels
Warming gels should not be used immediately after injury. At this time it is necessary to use on the contrary coolants. It is best to briefly apply ice anduse a cold compress. Athletes use special cooling sprays. Then you can apply a cooling gel, for example with menthol. Cooling prevents the development of edema and inflammation, anesthetizes. Cold should be applied on the first day after injury. After 2-3 days, they begin to use warming agents that increase local blood flow, which contributes to the resorption of hematomas.
Determination of gel strength
Manufacturers of medical, pharmaceutical, cosmetic gels need to know their hardness. The elasticity and rupture strength of gels is important for the manufacture of coronary stents, the material of which should be similar in mechanical properties to living tissue; contact lenses, suppositories, gel lubricants, microbial culture nutrients. The strength of gels is important in the manufacture of toothpastes, creams, lozenges.
To determine the strength of the gel according to Bloom, use the Bloom device. It determines the load required to push the gel surface with a cylindrical nozzle of a certain diameter (12.7 mm) to a depth of 4 mm.
What is a gel? These are dispersed systems that are characterized by a certain structure that gives them the properties of solids. Gels consist of at least two components, one of which is continuously distributed in the other. They can be obtained by coagulation of sols. Gels are characterized by the phenomenon of swelling. We hope that if the exam asks you: "Describe the concept of "gels"!", You can easily do it!
