**2. Colloids**

Colloids are systems formed by macromolecules or particles dispersed in a medium, in which one or more components have at least one of their dimensions within the range of 1 nm to 1000 nm [4].

Colloidal systems have been used since the dawn of humanity. Ancient people used gels from natural products as food, clay dispersions for the manufacture of ceramic utensils and colloidal pigment dispersions to decorate cave walls [5].

Colloidal systems are present in our daily lives in several products and technologies, such as personal hygiene (shampoo, toothpaste, foam, shaving cream, makeup, cosmetics) and in food (milk, coffee, butter, vegetable creams, fruit jellies, beer, soda or ice cream). During a single day we are consuming several colloids [5]. Colloids are also present in several consumer goods production processes, including drinking water, in the separation processes in the biotechnology industries and in the treatment of the environment.

In addition, colloidal phenomena are frequently used in industrial processes for the production of polymers, detergents, paper, soil analysis, food products, fabrics, precipitation, chromatography, ion exchange, flotation and heterogeneous catalysis. In orthomolecular therapeutic medicine, knowledge of the properties of colloidal systems can assist in the elucidation of diseases, such as Alzheimer's and Parkinson's [5].

#### **2.1 Colloid characteristics**

The factors that most contribute to the characteristics of a colloid are:


Colloids have specific characteristics such as high mass, high particle area/volume ratio and are relatively large. On the separation surfaces (interfaces) between the dispersed phase and the dispersion medium, characteristic surface phenomena are manifested, such as adsorption and double electrical layer effects, phenomena of great importance in determining the physicochemical properties of the system as a whole [6].

Depending on the affinity between the particles of a dispersion and the medium in which they are dispersed, we can classify colloids in two ways: lyophilic and lyophobic colloids. Lyophilic colloids are those in which the particle surface has an affinity for the solvent, keeping the dispersion more stable and minimizing aggregation. Lyophobic colloids, on the other hand, are those in which the particles have greater interaction with each other, which ends up leading to a rapid aggregation process [7].

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**Table 1.**

**2.3 Colloid preparation**

*Colloidal Stability of Cellulose Suspensions DOI: http://dx.doi.org/10.5772/intechopen.94490*

Regarding the colloid classification, there are the following categories:

• Emulsion: are colloids formed by liquid dispersed in another liquid.

continuous and dispersed phases, and examples found in everyday life.

are soluble with each

Example: soap foam, shaving cream, whipped cream

Example: pumice, expanded polystyrene

*Classification of colloids according to the dispersed phase and dispersion medium.*

**Scattered**

other

Liquid Liquid foam

Solid Solid foam

Dispersant Gas Does not exist. All gases

• Sol: are colloids formed by the dispersion of a solid in a liquid or solid.

• Gel: solid of gelatinous material formed from a colloidal dispersion, in which the dispersed is in the liquid state and the dispersant in the solid state.

The **Table 1** shows some different types of colloids according to the state of the

**Gas Liquid Solid**

Aerosol Liquid Examples: cloud, fog

Emulsion Examples: milk, honey, mayonnaise,

creams

Examples: gelatin, cheese, jam

Gel

Aerosol solid Examples: smoke, dust in suspension

Example: paints, colored glass

Sol

Solid Sun Example: ruby and sapphire crystal, metal alloys

Colloidal systems can be divided into three types: colloidal dispersions, true

Colloidal dispersions are heterogeneous systems composed of two or more phases, as shown in **Table 1**, and these systems are thermodynamically unstable, due to their high surface free energy. In a colloidal dispersion, the interfacial area of the dispersed phase is very large, which requires a lot of energy to keep it dispersed. In an attempt to minimize the free energy of the surface, the system tends to minimize

True macromolecule solutions are thermodynamically stable colloidal systems, that is, they will not separate phase. Polymeric solutions are examples of this class of colloids. Association colloids, which are also thermodynamically stable, are formed by the association of surfactant molecules, that is, micellar aggregates [8].

For the production of colloids there are two groups with different production

methods, they are: dispersion methods and condensation methods [3].

macromolecule solutions and association colloids [8].

the area, based on the aggregation of the dispersed phase [8].

• Aerosol: consists of a solid or a liquid dissolved in a gas.

• Foam: consists of a gas dispersed in solid or liquid.

**2.2 Colloid classification**
