The main topic of this article will be a colloidal particle. Here we will consider the concept of colloidal solution and micelles. And also get acquainted with the main species diversity of particles related to colloidal. We will dwell separately on the various features of the term under study, some individual concepts and much more.
The concept of a colloidal particle is closely related to various solutions. Together, they can form a variety of microheterogeneous and dispersed systems. The particles that form such systems usually range in size from one to one hundred microns. In addition to the presence of a surface with clearly separated boundaries between the dispersed medium and the phase, colloidal particles are characterized by the property of low stability, and the solutions themselves cannot form spontaneously. The presence of a wide variety in the structure of the internal structure and sizes causes the creation of a large number of methods for obtaining particles.
The concept of a colloidal system
In colloidal solutions, particles in all theiraggregates form systems of a dispersed type, which are intermediate between solutions, which are defined as true and coarse. In these solutions, drops, particles, and even bubbles that form the dispersed phase have sizes from one to a thousand nm. They are distributed in the thickness of the dispersed medium, as a rule, continuous, and differ from the original system in composition and/or state of aggregation. To better understand the meaning of such a terminological unit, it is better to consider it against the background of the systems it forms.
Among the properties of colloidal solutions, the main ones can be determined:
- Forming particles do not interfere with the passage of light.
- Transparent colloids have the ability to scatter light rays. This phenomenon is called the Tyndall effect.
- The charge of a colloidal particle is the same for dispersed systems, as a result of which they cannot occur in solution. In Brownian motion, dispersed particles cannot precipitate, which is due to their maintenance in a state of flight.
Basic classification units of colloidal solutions:
- A suspension of solid particles in gases is called smoke.
- A suspension of liquid particles in gases is called fog.
- From small particles of a solid or liquid type, suspended in a gas medium, an aerosol is formed.
- A gas suspension in liquids or solids is called foam.
- Emulsion is a liquid suspension in a liquid.
- Sol is a dispersed systemultramicroheterogeneous type.
- Gel is a suspension of 2 components. The first creates a three-dimensional framework, the voids of which will be filled with various low molecular weight solvents.
- A suspension of solid-type particles in liquids is called a suspension.
In all these colloidal systems, particle sizes can vary greatly depending on their nature of origin and state of aggregation. But even despite such an extremely diverse number of systems with different structures, they are all colloidal.
Species diversity of particles
Primary particles with colloidal dimensions are divided into the following types according to the type of internal structure:
- Suspensoids. They are also called irreversible colloids, which are unable to exist on their own for long periods of time.
- Micellar-type colloids, or, as they are also called, semi-colloids.
- Reversible type colloids (molecular).
The processes of formation of these structures are very different, which complicates the process of understanding them at a detailed level, at the level of chemistry and physics. Colloidal particles, from which these types of solutions are formed, have extremely different shapes and conditions for the process of formation of an integral system.
Determination of suspensoids
Suspensoids are solutions with metal elements and their variations in the form of oxide, hydroxide, sulfide and other s alts.
Allthe constituent particles of the aforementioned substances have a molecular or ionic crystal lattice. They form a phase of a dispersed type of substance - a suspensoid.
A distinctive feature that makes it possible to distinguish them from suspensions is the presence of a higher dispersion index. But they are interconnected by the lack of a stabilization mechanism for dispersion.
The irreversibility of suspensoids is explained by the fact that the sediment of the process of their steaming does not allow a person to get sols again by creating contact between the sediment itself and the dispersed medium. All suspensoids are lyophobic. In such solutions are called colloidal particles related to metals and s alt derivatives that have been crushed or condensed.
The production method is no different from the two ways that disperse systems are always created:
- Obtaining by dispersion (grinding large bodies).
- The method of condensation of ionic and molecularly dissolved substances.
Determination of micellar colloids
Micellar colloids are also referred to as semi-colloids. The particles from which they are created can arise if there is a sufficient level of concentration of amphiphilic type molecules. Such molecules can only form low molecular weight substances by associating them into a molecule aggregate - a micelle.
Molecules of amphiphilic nature are structures consisting of a hydrocarbon radical with parameters and properties similar to a non-polar solvent and a hydrophilic group, whichalso called polar.
Micelles are specific agglomerations of regularly spaced molecules that are held together predominantly through the use of dispersive forces. Micelles are formed, for example, in aqueous solutions of detergents.
Determination of molecular colloids
Molecular colloids are high-molecular compounds of both natural and synthetic origin. The molecular weight can range from 10,000 to several million. Molecular fragments of such substances have the size of a colloidal particle. The molecules themselves are called macromolecules.
Compounds of a macromolecular type subject to dilution are called true, homogeneous. They, in the case of extreme dilution, begin to obey the general series of laws for diluted formulations.
Getting colloidal solutions of molecular type is a fairly simple task. It is enough to make the dry substance and the corresponding solvent come into contact.
The non-polar form of macromolecules can dissolve in hydrocarbons, while the polar form can dissolve in polar solvents. An example of the latter is the dissolution of various proteins in a solution of water and s alt.
Reversible these substances are called due to the fact that subjecting them to evaporation with the addition of new portions of dry residues causes molecular colloidal particles to take the form of a solution. The process of their dissolution must go through a stage in which it swells. It is a characteristic feature that distinguishes molecular colloids, onagainst the background of other systems discussed above.
In the process of swelling, the molecules that form the solvent penetrate into the solid thickness of the polymer and thereby push the macromolecules apart. The latter, due to their large size, begin to slowly diffuse into solutions. Externally, this can be observed with an increase in the volumetric value of polymers.
Micelles of the colloidal system and their structure will be easier to study if we consider the forming process. Let's take an AgI particle as an example. In this case, particles of a colloidal type will be formed during the following reaction:
AgNO3+KI à AgI↓+KNO3
Molecules of silver iodide (AgI) form practically insoluble particles, inside which the crystal lattice will be formed by silver cations and iodine anions.
The resulting particles initially have an amorphous structure, but then, as they gradually crystallize, they acquire a permanent appearance.
If we take AgNO3 and KI in the corresponding equivalents, then the crystalline particles will grow and reach significant sizes, exceeding even the size of the colloidal particle itself, and then quickly precipitate.
If you take one of the substances in excess, then you can artificially make a stabilizer out of it, which will report on the stability of colloidal particles of silver iodide. In case of excessive AgNO3the solution will contain more positive silver ions and NO3-. It is important to know that the process of formation of AgI crystal lattices obeys the Panet-Fajans rule. Therefore, it is able to proceed only in the presence of ions that make up this substance, which in this solution are represented by silver cations (Ag+).
Positive Argentum ions will continue to be completed at the level of formation of the crystal lattice of the core, which is firmly included in the micelle structure and communicates the electrical potential. It is for this reason that the ions that are used to complete the construction of the nuclear lattice are called potential-determining ions. During the formation of a colloidal particle - micelles - there are other features that determine one or another course of the process. However, everything was considered here using an example with the mention of the most important elements.
The term colloidal particle is closely related to the adsorption layer, which is formed simultaneously with ions of a potential-determining type, during the adsorption of the total amount of counterions.
A granule is a structure formed by a core and an adsorption layer. It has an electric potential of the same sign as the E-potential, but its value will be smaller and depends on the initial value of counterions in the adsorption layer.
Coagulation of colloidal particles is a process called coagulation. In dispersed systems, it leads to the formation of small particleslarger ones. The process is characterized by cohesion between small structural components to form coagulative structures.