Lakhasly

Stability of colloidal solutions

There are two types of stability for colloid solution: sedimentation stability and aggregation stability.Coagulation threshold is the minimal concentration of a given electrolyte that

causes visible coagulation of a certain sol.So, the coagulation threshold (C) is calculated from the molarity of electrolyte solution (C) and its volume (V), and from the volume of sol (V).Ccoagulation(CV)/(V+V)

The higher the coagulation threshold, the weaker the coagulative ability; and the lower the coagulative threshold, the stronger the coagulative ability of a given electrolyte.Electrostatic factor is determined by the electrokinetic potential (4).

Stability of colloidal solutions

There are two types of stability for colloid solution: sedimentation stability and aggregation stability. Sedimentation stability is the ability to overwhelm the gravity with the help of Brownian movement. Sedimentation stability is determined by: the size of particles (the smaller the better), and the viscosity of the medium (the higher the better).

Aggregation stability is determined by: electrostatic factor and adsorption- solvatation factor. Electrostatic factor is determined by the electrokinetic potential (4). The higher the value of 4, the stronger the repulsion between granules (because they have the same charge).

Coagulation of a colloid solution

One can cause coagulation of a colloid solution: by the increase in concentration of a solution, by the increase or the decrease in temperature, by different types of radiation, by the addition of an electrolyte.

Coagulation threshold is the minimal concentration of a given electrolyte that

causes visible coagulation of a certain sol.

To calculate this concentration one should take care aboutthe dilution of the sol. So, the coagulation threshold (C) is calculated from the molarity of electrolyte solution (C) and its volume (V), and from the volume of sol (V).

Ccoagulation(CV)/(V+V)

The higher the coagulation threshold, the weaker the coagulative ability; and the lower the coagulative threshold, the stronger the coagulative ability of a given electrolyte.

Coagulation includes three phases: hidden coagulation, visible slow coagulation and visible fast coagulation. As it is shown in figure 5.3, during the hidden coagulation the rate of coagulation is slowly increasing with the growth of concentration of added electrolyte. One cannot see that coagulation is already started during the hidden phase by the naked eye. However, in the ultramicroscope one can see that the size of particles is growing.