In nature, there are no elements that are pure. Basically, they are all different mixtures. They, in turn, can be heterogeneous or homogeneous. They are formed from substances in the state of aggregation, while creating a certain dispersion system in which various phases are present. In addition, a dispersion medium is usually present in mixtures. Its essence lies in the fact that it is considered an element with a large volume in which any substance is distributed. In a disperse system, the phase and medium are arranged so that there are particles of the interface between them. Therefore, it is called heterogeneous or heterogeneous. In view of this, the effect of the surface, and not of the particles as a whole, is of great importance.
Dispersed System Classification
The phase, as is known, is represented by substances having a different state. And these elements are divided into several types. The aggregate state of the dispersed phase depends on the combination of the medium in it, resulting in 9 types of systems:
- Gas. Liquid, solid and element in question. Homogeneous mixture, fog, dust, aerosols.
- The liquid dispersed phase. Gas, solid, water. Foams, emulsions, sols.
- The solid dispersed phase. Liquid, gas and the substance considered in this case. Soil, means in medicine or cosmetics, rocks.
As a rule, the size of a dispersed system is determined by the size of the phase particles. The following classification exists:
- rough (suspensions);
- thin (colloidal and true solutions ).
Particles of a dispersion system
When analyzing coarse mixtures, one can observe that particles of these compounds in the structure can be visible to the naked eye, because their size is more than 100 nm. Suspensions, as a rule, relate to a system in which the dispersed phase is separable from the medium. This is because they are considered opaque. Suspensions are divided into emulsions (insoluble liquids), aerosols (fine particles and solids), suspensions (solid in water).
A colloidal substance is any one that has the quality of having another element uniformly disperse over it. That is, it is present, or rather it is part of the dispersed phase. This is a condition when one material is completely distributed in another, or rather in its volume. In the milk example, liquid fat is dispersed in an aqueous solution. In this case, the smaller molecule is within 1 nanometer and 1 micrometer, which makes it invisible to an optical microscope when the mixture becomes homogeneous.
That is, no part of the solution has a greater or lesser concentration of the dispersed phase than any other. It can be said that it is colloidal in nature. The larger is called the continuous phase or dispersion medium. Since its size and distribution do not change, and the element in question spreads over it. Types of colloids include aerosols, emulsions, foams, dispersions, and mixtures called hydrosols. Each similar system has two phases: dispersed and continuous phase.
History Colloids
Intensive interest in such substances was present in all sciences at the beginning of the 20th century. Einstein and other scientists carefully studied their characteristics and applications. At that time, this new field of science was a leading field of research for theorists, researchers, and manufacturers. After the peak of interest until 1950, the study of colloids significantly decreased. It is interesting to note that with the recent emergence of higher-power microscopes and "nanotechnology" (the study of objects of a certain tiny scale), the scientific interest in the study of new materials is growing again.
More on these substances
There are elements observed both in nature and in artificial solutions with colloidal properties. For example, mayonnaise, cosmetic lotion, and lubricants are types of artificial emulsions, and milk is a similar mixture found in nature. Colloidal foams include whipped cream and shaving foam, while edible elements include butter, marshmallows and jellies. In addition to food, these substances exist in the form of certain alloys, paints, inks, detergents, insecticides, aerosols, polystyrene foam and rubber. Even beautiful natural objects, such as clouds, pearls and opals, have colloidal properties because they have another substance evenly distributed through them.
Preparation of colloidal mixtures
By enlarging small molecules to a range of 1 to 1 micrometer, or by reducing large particles to the same size. Colloidal substances can be obtained. Further production depends on the type of elements used in the dispersed and continuous phases. Colloids behave differently than regular fluids. And this is observed in transport and physico-chemical properties. For example, a membrane can allow a true solution with solid molecules attached to liquid to pass through it. While a colloidal substance, which has a solid dispersed through a liquid, will be stretched by the membrane. The parity of the distribution is uniform to the point of microscopic equality in the gap throughout the second element.
True solutions
The colloidal dispersion has the form of a homogeneous mixture. An element consists of two systems: a continuous and a dispersed phase. This indicates that this case is associated with true solutions, because they are directly related to the above mixture, consisting of several substances. In a colloid, the second has the structure of the smallest particles or drops, which are evenly distributed in the first. From 1 nm to 100 nm is the size of the dispersed phase, or rather particles, in at least one dimension. In this range, the dispersed phase is a homogeneous mixture with the indicated dimensions. Examples of elements that are suitable for the description can be called colloidal aerosols, emulsions, foams, hydrosols. Particularly exposed to the chemical composition of the surface are particles or droplets present in the formulations under consideration.
Colloidal solutions and systems
It should be borne in mind that the size of the dispersed phase is a difficult to measure variable in the system. Solutions are sometimes characterized by their own properties. To make it easier to perceive the composition indicators, their colloids resemble and look almost the same. For example, if it is dispersed in a liquid, solid form. As a result, particles will not pass through the membrane. While other components like dissolved ions or molecules are able to pass through it. If it is easier to analyze, it turns out that the dissolved components pass through the membrane, and with the phase in question, colloidal particles cannot.
The appearance and disappearance of color characteristics
Due to the Tyndall effect, some of these substances are translucent. In the structure of an element, it is the scattering of light. Other systems and compositions are with some shade or even be opaque, with a certain color, even if some are dim. Many familiar substances, including butter, milk, cream, aerosols (fog, smog, smoke), asphalt, paints, paints, glue and sea foam, are colloids. This field of study was introduced in 1861 by the Scottish scientist Thomas Graham. In some cases, a colloid can be considered as a homogeneous (not heterogeneous) mixture. This is because the distinction between “dissolved” and “granular” material can sometimes be the subject of an approach.
Hydrocolloid types of substances
This component is defined as a colloidal system in which particles are dispersed in water. Hydrocolloid elements, depending on the amount of liquid, can take on various conditions, for example, a gel or a sol. They are irreversible (single-component) or reversible. For example, agar, the second type of hydrocolloid. It can exist in a state of gel and sol, and alternate between states with the addition or removal of heat.
Many hydrocolloids are obtained from natural sources. For example, carrageenan is extracted from algae, gelatin has bovine fat, and pectin from the peel of citrus fruits and apple cake. Hydrocolloids are used in foods mainly for influencing texture or viscosity (sauce). Also used for skin care or as a healing agent after an injury.
Essential characteristics of colloidal systems
From this information it can be seen that colloidal systems are a subsection of the dispersed sphere. They, in turn, can be solutions (sols) or gels (jellies). The first in most cases are created on the basis of living chemistry. The latter are formed under sediments that occur during the coagulation of sols. Solutions can be aqueous with organic matter, with weak or strong electrolytes. The particle size of the dispersed phase of the colloids is from 100 to 1 nm. They cannot be seen with the naked eye. As a result of sedimentation, the phase and the medium are difficult to separate.
Classification by type of particles of the dispersed phase
Multimolecular colloids. When, when dissolved, atoms or smaller molecules of substances (having a diameter of less than 1 nm) are combined together to form particles of similar sizes. In these sols, the dispersed phase is a structure that consists of aggregates of atoms or molecules with a molecular size of less than 1 nm. For example, gold and sulfur. In these colloids, the particles are held together by van der Waals forces. They are usually lyophilic in nature. This means significant particle interaction.
High molecular weight colloids. These are substances having large molecules (the so-called macromolecules), which upon dissolution form a certain diameter. Such substances are called macromolecular colloids. These dispersed phase constituents are typically polymers having very high molecular weights. Natural macromolecules are starch, cellulose, proteins, enzymes, gelatin, etc. Artificial polymers include synthetic polymers such as nylon, polyethylene, plastics, polystyrene, etc. They are usually lyophobic, which means in this case a weak interaction particles.
Bound colloids. These are substances that, when dissolved in a medium, behave like normal electrolytes at a low concentration. But they are colloidal particles with a larger enzyme component of the components due to the formation of aggregated elements. The aggregate particles thus formed are called micelles. Their molecules contain both lyophilic and lyophobic groups.
Micelles. They are cluster or aggregated particles formed by the association of a colloid in solution. Common examples are soaps and detergents. The formation occurs above a certain Kraft temperature, and above a certain critical concentration of micellization. They are able to form ions. Micelles can contain up to 100 molecules or more, for example, sodium stearate is a typical example. When it dissolves in water, it gives ions.