1. Micro geterogeneous systems. Colloidal solutions.
Kharkiv National Medical University
Department of
Medical and Bioorganic chemistry
«Medical Chemistry»
Lecture № 9
Micro geterogeneous systems.
Colloidal solutions.
Coarsely dispersed systems
Lecturer: As. Professor,
Department of Medical and Bioorganic Chemistry,,
Ph.D. Lukianova L.V.

2. Plan of lecture
1. Dispersed systems: general aspects, classification. 2. Methods of preparation of colloidal solutions. 3. Methods of colloidal solutions purification. 4. Properties of colloidal solutions. 5. Structure of micelles. 6. Stability and coagulation of the dispersed systems. 7. Coagulation by means of electrolytes. 8. Coagulation in the biological systems. 9. Coarsely dispersed systems.

3. The most important biological liquids such as blood, urine and spinal fluid contain slightly soluble substances in colloid state: cholesterol, carbonate, phosphate, urate, and salts of other acids. Break of their stability causes their precipitation resulting in arteriosclerosis, holelithiasis, urolithiasis, etc. Knowledge of coagulation and stability of the dispersed, systems is necessary to understand processes taking place in the human organism, because a large number of biological fluids in the organism are colloidal systems. One of the most important characteristics of blood is red corpuscles sedimentation rate (RCSR) which increases if some kind of pathology takes place. Coagulation phenomena become clearly seen in the process of blood coagulation. The nature of blood coagulation must be taken into account during the blood conservation as well as in the process of creation of new medicinal materials possessing antithrombotic properties.

4. Colloidal chemistry
Colloidal chemistry – the science of surface phenomena and dispersed systems.
Surface phenomena – a set of phenomena associated with the physical characteristics of the interfaces between contiguous phases.
Dispersed Systems – heterogeneous system in which one phase is dispersed in the (fragmented state).

5. Dispersed phase (fractured part dispersed system)
Colloidal solution
Dispersed phase (fractured part dispersed system)
Dispersion medium
(continuous part of the dispersion system)
Dispersed
phase
Dispersion
medium

6. Dispersed systems are classified according to:
Dispersed system – is a system consisting of dispersed particles and the medium in which these are suspended.
Dispersed systems are classified according to:
their dispersity;
the state of aggregation of the dispersed phase and the dispersion medium;
the intensity of the interaction between them;
the absence or formation of structures in the dispersed systems.

7. Classification of dispersed systems on the base of particles size
True solutions – size of particles is < 10-9 m, particles of solute are molecules or ions
Colloids – size of particles is m, particles of intermediate size
Coarsely dispersed systems – size of particles is > m, particles of solute are insoluble in a given solvent (suspensions, emulsions).

8. Classification of the state of aggregation
of the dispersed phase and the dispersion medium
Dispersed phase
Dispersion medium
Type of dispersed system
Example
Gas
Liquid
Foam
soap lather, whipped cream, soda water
Solid
Solid foam
bread, pumice, slag, foam concrete, lava
Aerosol
fog, cloud, spray
Emulsion
milk, mayonnaise, oil in water
Solid emulsion
pearls, cheese, curd, jelly, butter
Aerosol, powder
smoke, haze, dust-laden air, flour
Suspension (coarsely dispersed) or sol (highly dispersed)
paints, clay, starch dispersed in water
Solid sol
alloys, colored glass, gems (ruby, emerald, black diamond)

9. Depending upon the nature of interactions between dispersed phase and dispersion medium, the colloidal solutions can be classified into two types as: lyophilic and lyophobic sols.
Lyophilic colloids – the colloidal solutions, in which the particles of the dispersed phase have a great affinity for the dispersion medium.
Lyophobic colloids – the colloidal solutions in which there is no affinity between particles of the dispersed phase and the dispersion medium.

10. Dispersed systems are very widely spread in nature!
Soils, clays, natural water, air, clouds, dust, minerals (including precious stones), bread, milk, butter – are colloidal systems.
Cells, genes, viruses – are colloidal particles.
Biological liquids – blood, lymph, urine, cerebrospinal fluid – are colloidal dispersions. In these liquids substances, e.g. proteins, cholesterine, glycogen and others are present being in colloidal state.
Finely dispersed substances easily penetrate through the pores of skin. Medicines in the form of colloids (emulsions, ointments, pastes, aerosols) are widely used in medicine.

11. Obtaining of colloidal solution
1. By the dispersion, i.e. comminution of large bodies. Comminution by crushing, grinding, or attrition yields comparatively coarsely dispersed powders (over 60 mm size). Finer comminution is achieved with the aid of special equipment named colloid mills, or by employing ultrasound.
2. By the condensation of substances forming molecular or ionic solutions. The condensation method consists in the obtaining of insoluble compounds by chemical reactions of exchange, hydrolysis, reduction, or oxidation.

12. 3. Methods of colloidal solutions purification
1. Dialysis – the process of separating the particles of colloids from impurities by means of diffusion through a suitable membrane. Its principle is based upon the fact that colloidal particles cannot pass through a parchment or cellophane membrane while the ions of the electrolyte can pass through it. The ordinary process of dialysis is slow. To increase the process of purification, the dialysis is carried out by applying electric field. This process is called electrodialysis. 2. Ultra-filtration. It is the process of removing the impurities from the colloidal solution by passing it through graded filter papers called ultra-filter papers.

13. Properties of colloidal solutions
Colligative properties are negligible small.
Optical properties. Colloidal systems scatter the light (Tyndall effect).
Molecular-Kinetic properties:
a) Brownian movement;
b) diffusion;
c) sedimentation
4. Electrical properties:
a) electrophoresis;
b) electroosmosis

14. Structure of colloidal particle (micelle)
Pb(NO3) NaCl → PbCl2↓ + 2NaNO3
NaCl
Pb(NO3)2
[PbCl2]m
nucleus

15. {[PbCl2]mnCl-(n-x)Na+}-xxNa+
nucleus
potential-
determining ions
inner layer of ions
granule
Na+
[PbCl2]m
Cl-
gegenions
diffuse layer of ions
nucleus
potential-determining
ions
gegenions
diffuse layer of
inner layer of ions
granule
{[PbCl2]mnCl-(n-x)Na+}-xxNa+

16. Electrical double layer
Micelle has electrical double layer.
{[PbCl2]mnCl-(n-x)Na+}-x xNa+
ε-potential
(electrothermodynamic potential)
ζ-potential (electrokinetic potential)
ζ-potential determines the rate of movement of particles in the electric field. The granule of given micelle will move to the anode, while ions of diffuse layer will move to the cathode.

17. If all gegenions are in the inner layer, ζ-potential becomes equal zero and micelle is said to be in isoelectric state.
{[PbCl2]mnCl-nNa+}0
The thickness of electrical double layer and the value of ζ-potential depend on concentration of solution. ζ-potential decreases with increase in concentration. In isoelectric state colloidal systems are unstable.
The movement of dispersed phase particles in electric field is called electrophoresis. The rate of movement depends on ζ-potential value.
Electrophoresis is widely used for aminoacids, antibiotics, enzymes, antibodies and other objects separation. It is also used for plasma proteins investigations with diagnostic purposes.

18. {[PbCl2]mnCl-(n-x)Na+}-xxNa+
Micelles with different charges of granule can be obtained depending upon the substance which is present in surplus.
Pb(NO3) NaCl → PbCl2↓ + 2NaNO3
NaCl
Pb(NO3)2
{[PbCl2]mnCl-(n-x)Na+}-xxNa+
Negatively charged sol
surplus
NaCl
Pb(NO3)2
{[PbCl2]mnPb2+(2n-x)NO3-}+x xNO3-
Positively charged sol
surplus

19. Conditions for colloidal systems obtaining
1. An essential condition for colloidal systems obtaining is the mutual insolubility of the substance being dispersed and the dispersion medium.
2. One reagent (it is stabilizer) must be in a small surplus
3. Nucleus of a colloidal micelle – is an insoluble product
4. Potential-determining ions are common for the nucleus and for the stabilizer
5. Gegenions come from the stabilizer.
FeSO4 + Na2S → FeS↓ + Na2SO4
surplus
FeSO4 + Na2S → FeS↓ + Na2SO4
surplus
{[FeS]mnFe2+(n-x)SO42-}+x xSO42-
{[FeS]mnS2-(2n-x)Na+}-x x Na+

20. Emulsions
The various pharmaceuticals widely used in medicine are colloidal or coarsely dispersed systems. These are: suspensions, ointments, aerosols, powders, emulsions, pastes.
Emulsions are the coarsely dispersed systems of two immiscible liquids in which the liquid acts as the dispersed phase as well as the dispersion medium. They are obtained by mixing an oil with water. Since the two do not mix well, the emulsion is generally unstable and is stabilized by adding emulsifier or emulsifying agent (gum, soap, glass powder, etc).
There are two types of emulsions:
1. Oil-in-water emulsion (aqueous emulsions)
2. Water-in-oil emulsion (oily emulsions)

21. Stability and coagulation of dispersed systems
Stability – constant in time the main parameters of the disperse system: the degree of dispersion and uniform distribution of the dispersed phase in the dispersion medium.
Coagulation – the process of destruction of colloidal systems by sticking particles form larger aggregates and loss of stability, followed by separation.

22. Rules electrolyte coagulation
Coagulation of sols with electrolytes
Rules electrolyte coagulation
All electrolytes at certain concentrations can cause coagulation of the sol.
The rule of sign of the charge: the coagulation of the sol causes the ion electrolyte, the sign of the charge which is opposite to the charge of the colloidal particles. This ion is called an ion-coagulator.
Each electrolyte relative to the colloidal solution has a threshold of coagulation (coagulating ability).

23. Coagulation ability (P) – the inverse of the threshold of coagulation
Coagulation threshold (γ, C) – the lowest concentration of the electrolyte sufficient to cause coagulation of the sol
Coagulation ability (P) – the inverse of the threshold of coagulation
Effect of ion charge-coagulator (Schulze-Hardy rule): coagulation ability of the electrolyte increases with increasing ion charge-coagulator
n = 2 ÷ 6

24. Thank you for your attention!