In the Russian language there are three terms that are similar to each other - gels, jellies and jellies. In terms of structure, there is not much difference between them, but these concepts are applied in different fields of activity. The term “gel” is more often used in chemistry or in relation to medicines and cosmetics, “jelly” in cooking, less often in chemistry, and “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 "motionless, frozen."
The definition is given by colloidal chemistry - a science that studies dispersed systems and surface phenomena.
What is a gel in terms of chemistry? A gel is such a dispersed system with a dispersion medium in which phase particles form a spatial structural network. The gel contains at least two components.
Gel - colloidal system
Dispersed systems are those in which particles of one substance are evenly distributed among particles of another substance. In such systems, they distinguish:
- dispersion medium - the substance in which the distribution occurs,
- dispersed phase - a substance whose particles are distributed.
The dispersion system, for example, is fog. Here, the dispersion medium is gaseous, its role is air, and the dispersed phase is liquid, it is the particles of water 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 greatest degree of phase refinement — to individual molecules — is in true solutions. There is no interface between particles - molecules of phase and medium. Such systems are called homogeneous, they are stable. Examples of true solutions: sulfuric acid solution , air, sea water, cast iron.
In coarse dispersed 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 they stratify over time. Examples of coarse systems: ground chalk in water, whitewash, mortar, toothpaste, vegetable oil in water, milk.
Phase particles 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 with time under the influence 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 dispersed systems are distinguished. If the medium is gas, then the phase can be a liquid (we have already considered fog) or a solid. For example, smoke or smog - particles of a 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 suspension, depending on the size of the particles. Gels are obtained from sols under certain conditions.
By definition of chemistry, gels are dispersed systems in which a dispersion medium is a solid substance, a dispersed phase is a liquid. That is, gel is the name of the type of dispersion system along with an emulsion, aerosol, suspension, etc.
Gels - fluid loss solutions
Some solutions of macromolecular substances and sols during long-term storage can turn into gels. IUD particles or sols are bonded to each other, forming a continuous grid. Particles of solvent penetrate inside such a network. Thus, the dispersion medium and the dispersed phase change their roles. The phase becomes continuous, and the particles of the medium become isolated. So, 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 exfoliate over time, with spontaneous release of fluid. This phenomenon is called syneresis. There is a densification of the spatial network, a decrease in the volume of the gel, and the formation of the so-called solid colloid.
The formation of a solid colloid from a gel is a common natural occurrence. For example, the essence of blood coagulation is the conversion of fibrinogen, a soluble protein, into fibrin, an insoluble protein. Under normal conditions, blood coagulation 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 during prolonged storage begin to secrete liquid and become unusable.
The processes of converting sol to gel and gel to solid colloid are reversible. For example, the gelatin protein, which is a solid colloid, when swollen in water, turns into a gel - gel. It is important to observe the temperature regime, bring the gelatin to a boil, but not boil, otherwise the structure is destroyed, and the gel turns into sol, acquiring fluidity.
When dried, the gels are irreversibly destroyed.
Gel classification
Depending on the chemical nature of the dispersion medium, gels are distinguished: hydrogels, alcohol, benzogels, etc. Gels that are poor in liquid or completely anhydrous are called xerogels. Xerogel is carpentry glue in tiles, starch, dry sheet gelatin. Complex xerogels are cookies, flour, crackers.
Some gels contain little dry matter, but still have a spatial structure. This jelly, jelly, yogurt, soap solutions. They are called lyogels.
A group of coagels is isolated. These are gelatinous precipitates, which are obtained by coagulating sols (silicic acid, iron (III) hydroxide, etc.) and salting out polymer solutions. In coagels, the dispersion medium forms a separate phase, only a small part of the medium is connected.
The use and importance of gels in medical practice
In medicine, gels are used:
- when conducting ultrasound and electrographic studies;
- to create artificial joints, ligaments;
- to stop bleeding with blockage (embolism) of blood vessels;
- to restore the cornea;
- antibacterial, antiviral gels;
- warming gels for pain relief of various parts of the musculoskeletal system;
- cooling gels for injuries.
Warming gels
Warming gels increase the permeability of capillaries due to the components included in their composition - this is bee and snake venom, pepper extract; methyl salicylate has a less pronounced effect. These components cause an increase in blood supply to the vessels - hyperemia, thereby increasing local heat transfer. Warming gels are applied topically for various lesions of the musculoskeletal system - joints, muscles, ligaments, tendons. They are used to relieve swelling, reduce soreness, activate blood circulation in the affected area. Warming gels are used by athletes before training to prepare muscles. Muscle tissue under the action of gel components warms up and therefore is less damaged during exercise, which prevents stretching and injury. Using such gels after exercise helps relieve muscle tension and fatigue.
Popular warming gels are made on the basis of:
- capsaicin pepper or its synthetic analogue - "Finalgon", "Capsicam";
- the poison of bees and snakes - "Viprosal";
- diclofenac, ibuprofen, indomethacin - non-steroidal anti-inflammatory substances - "Diclofenac", "Ortofen", "Indomethacin".
When using warming agents, it is necessary to 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 an injury. At this time, it is necessary to use coolants on the contrary. It is best to briefly apply ice and use 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 an injury. After 2-3 days, they start using warming agents that enhance local blood flow, which helps resorption of hematomas.
Determination of gel strength
Manufacturers of medical, pharmaceutical, and cosmetic gels need to know their hardness. The elasticity and breaking strength of gels is important for the manufacture of coronary stents, the material of which must be similar in mechanical properties to living tissue; contact lenses, suppositories, gel-like lubricants, nutrients for the cultivation of microorganisms. The strength of gels is important in the manufacture of toothpastes, creams, lozenges.
To determine the strength of the gel according to Bloom, use a Bloom device. It determines the load required to force the gel surface into a cylindrical nozzle with a specific diameter (12.7 mm) to a depth of 4 mm.
What is a gel? These are dispersed systems, which are characterized by a certain structure that gives them the properties of solids. Gels consist of at least two components, one of them is continuously distributed in the other. They can be obtained by coagulation of sols. For gels, a swelling phenomenon is characteristic. We hope that if you are asked at the exam: "Describe the concept of" gels "!", You can easily do it!