The main topic of this article will be a colloidal particle. Here we consider the concept of colloidal solution and micelles. And also get acquainted with the main species diversity of particles related to colloidal. We dwell separately on the various features of the studied term, some individual concepts, and much more.
Introduction
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 forming such systems are usually in size ranging 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 size causes the creation of a large number of methods for producing particles.
The concept of colloidal system
In colloidal solutions, particles in their entirety form disperson-type systems that are intermediate between solutions, which are defined as true and coarsely dispersed. In these solutions, droplets, particles, and even bubbles that form the dispersed phase have a size of one to one thousand nm. They are distributed in the bulk 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 that it forms.
Property Definition
Among the properties of colloidal solutions, the main ones can be determined:
- The forming particles do not interfere with the passage of light.
- Transparent colloids have the property of scattering light rays. This phenomenon is called the Tyndall effect.
- The charge of the colloidal particle is the same for dispersed systems, as a result of which they cannot be found in solution. In the Brownian motion, dispersed particles cannot precipitate, which is caused by their maintenance in flight.
Main types
The main classification units of colloidal solutions:
- A suspension of particles of a solid type in gases is called smoke.
- A suspension of particles of liquid in gases is called fog.
- Aerosol is formed from small particles of solid or liquid type suspended in a gas medium.
- Gas suspension in liquids or solids is called foam.
- An emulsion is a liquid suspension in a liquid.
- Sol is a dispersed system of ultramicroheterogeneous type.
- A 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 particles of a solid type 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, all of them are colloidal.
Species diversity of particles
Primary particles having colloidal sizes, according to the type of internal structure, are divided into the following types:
- Suspenzoids. They are also called irreversible colloids, which are not able to exist independently in long periods of time.
- Colloids are micellar type, or, as they are also called, semi-colloids.
- Reversible type (molecular) colloids.
The processes of formation of these structures are very different from each other, which complicates the process of understanding them at a detailed level, at the level of chemistry and physics. The colloidal particles from which such types of solutions are formed have very different shapes and conditions for the formation of a whole system.
Suspension Definition
Suspension is called a solution with metal elements and their variations in the form of oxide, hydroxide, sulfide and other salts.
All forming particles of the above substances have a molecular or ionic crystal lattice. They form a phase of a dispersed type of substance - a suspensionoid.
A distinctive feature that allows them to be distinguished from suspensions is the presence of a higher dispersion index. But they are interconnected by the absence of a stabilization mechanism for dispersion.
The irreversibility of suspensoids is explained by the fact that the precipitate of the process of their evaporation prevents the person from getting sols again by creating contact between the precipitate itself and the dispersed medium. All suspensoids are lyophobic. In such solutions are called colloidal particles related to metals and derivatives of salts that have been crushed or condensed.
The production technique is no different from the two methods that disperse systems always create:
- Obtained by dispersion (grinding large bodies).
- The method of condensation of ionically 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 when there is a sufficient level of concentration of diphilic type molecules . Such molecules can form only low molecular weight substances through their association in the aggregate of the molecule - a micelle.
Molecules of a diphilic nature are structures consisting of a hydrocarbon radical with parameters and properties similar to a non-polar solvent and hydrophilic group, which is also called polar.
Micelles are special clusters of correctly spaced molecules that are retained primarily through the use of dispersed forces. Micelles are formed, for example, in aqueous solutions of detergents.
Determination of molecular colloids
Molecular colloids are macromolecular compounds of both natural and synthetic origin. Molecular weight can range from 10,000 to several million. Molecular fragments of such substances have a colloidal particle size. Molecules themselves are called macromolecules.
Compounds of high molecular weight type, subject to dilution, are called true, homogeneous. They, in the case of limiting dilution, begin to obey the general series of laws for diluted formulations.
The preparation of molecular type colloidal solutions is a fairly simple task. It is enough to make dry matter and the corresponding solvent contact.
The non-polar form of macromolecules can dissolve in hydrocarbons, and the polar form in polar solvents. An example of the latter is the dissolution of various proteins in a solution of water and salt.
These substances are called reversible due to the fact that exposure to their evaporation with the addition of new portions of solids causes molecular colloidal particles to take the form of a solution. The process of their dissolution must go through the stage at which it swells. It is a characteristic feature that distinguishes molecular colloids, against the background of other systems that were discussed above.
In the process of swelling, the molecules that form the solvent penetrate into the solid thickness of the polymer and thereby repel macromolecules. The latter, due to their large sizes, begin to slowly diffuse into solutions. Outwardly, this can be observed with an increase in the bulk size of the polymers.
Micelle device
The micelles of the colloidal system and their structure will be easier to study if we consider the forming process. Take for example the AgI particle . In this case, colloidal particles will form during the following reaction:
AgNO 3 + KI à AgI ↓ + KNO 3
Silver iodide (AgI) molecules 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 type structure, but then, as their gradual crystallization proceeds, they acquire a constant appearance.
If we take AgNO 3 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 we take one of the substances in excess, then we can artificially make a stabilizer out of it, which will report on the stability of colloidal particles of silver iodide. In case of excessive amounts of AgNO 3 the solution will contain more positive silver ions and NO 3 - . It is important to know that the formation of AgI crystal lattices follows the Panet-Faience rule. Therefore, it is able to proceed only in the presence of ions that are part of this substance, which in this solution are represented by silver cations (Ag + ).
The positive ions of the argentum will continue to be completed at the level of formation of the crystal lattice of the nucleus, which firmly enters the structure of the micelle and reports on the electric potential. It is for this reason that the ions that are used to complete the nuclear lattice are called potential-determining ions. In the course of 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.
Some concepts
The term colloidal particle is closely related to the adsorption layer, which is formed simultaneously with the potential-determining type ions, during the adsorption of the total number of counterions.
A granule is a structure formed by a core and an adsorption layer. It has an electric potential of the same sign with which the E potential is endowed, however, its value will be smaller and depends on the initial value of counterions in the adsorption layer.
Adhesion of colloidal particles is a process called coagulation. In disperse systems, it leads to the formation of larger particles from small particles. The process is characterized by adhesion between small structural components with the formation of coagulation structures.