Difference between associative colloid, molecular colloid and disperse colloid

According to the aggregation state of particles in the dispersed system or its formation method, the polydisperse system can be divided into three types: associative dispersed system, molecular dispersed system and liquid-phobic dispersed system. When the particle size is in the colloidal range, the above three systems are respectively called associative colloids, molecular colloids and dispersed colloids.

In the surfactant solution, due to the polarization of the active agent molecules, it is easy to associate to form micellar particles, and the size of the micelles is often in the colloidal size range. Therefore, the dispersion system formed in this way is called associative colloid. For example, soapy water in the oil-in-water system, micelles in emulsions, cell membranes in organisms, etc., as well as moisturizers in the water-in-oil system and micelles in drilling fluids are all association colloids. Even though the micelle diameter exceeds the range of colloids, we still call them associative colloids.

Molecular colloids are macromolecular solutions in which natural or synthetic macromolecules are dissolved in a medium to form molecular dispersions. Since its dispersed particles exist in the form of molecules, it is actually a solution, that is, a polymer solution. However, due to its large molecular weight, the molecular size has reached the size of the colloidal particle, so in many properties, such as the colligative property of the solution, viscosity, conductance, etc., are different from the small molecule solution, but similar to the colloid system, in the molecular Size and its dynamic properties, optical properties, rheological properties and other aspects also have properties and research methods similar to colloids. Therefore, polymer solutions have historically been discussed in colloid chemistry, known as molecular colloids. From the point of view of the affinity between the particle and the medium, there is a strong interaction between the polymer and the solvent, and the solvent can dissolve the polymer body to form a molecularly dispersed state. Therefore, there is an affinity between the polymer and the solvent, so this system is also called a lyophilic colloid. From a thermodynamic point of view, a polymer solution is a thermodynamically stable system, that is, when the external conditions such as temperature change cause the solute to precipitate and precipitate, once the external conditions such as temperature return to the original state, the precipitated macromolecular solute Redissolution is still possible and the process is reversible. For example, polyvinyl alcohol aqueous solution, butanone solution of epoxy resin, etc. are molecular colloids. But in this book, polymer solution is still used to represent this system, instead of molecular colloid, lyophilic colloid and other names.

Disperse colloid is a colloidal system formed by dispersing insoluble matter as a dispersed phase in a dispersion medium. This system has a large phase interface and is easily destroyed and coagulated. After coagulation, it often cannot return to its original state. Molecular colloids are essentially different. Dispersion colloids are irreversible systems that are thermodynamically unstable. When the external conditions such as temperature change and cause the colloidal particles to grow and settle, once the external conditions such as temperature return to the original state, the dispersed particles that have settled or grown cannot be automatically resolved and redispersed into the original colloidal particles and particles. In a decentralized state, the process is irreversible. Because there is no good affinity between the particle and the medium to make it stable, therefore, as opposed to the lyophilic colloid, this dispersoid is also called a lyophobic colloid. It is mainly this class of colloids that we are going to discuss. Hereinafter, those who only refer to colloids refer to such dispersed colloids.

Foam and emulsion are two special dispersion systems, which are respectively polydisperse systems composed of insoluble gases and insoluble liquids in the liquid phase. Their properties, especially interface properties, are closely related to colloidal dispersion systems. But it has some unique behavioral characteristics, so we discuss it in a separate chapter.

According to the aggregation state of the dispersed phase and the dispersed medium, the colloid can be divided into eight kinds of dispersed systems (below). Customarily, the dispersion medium is called aerosol, the dispersion medium is called solid sol, and the medium is called liquid sol. When the liquid medium is water, it is called a hydrosol.

The characteristic of colloidal dispersion system is that the specific surface area of ​​the particles in the system is large, and there is an obvious interface between the dispersed phase and the dispersion medium. The system is a two-phase or multi-phase inhomogeneous system, so many properties of the colloid are related to the interface properties.