Disperse systems. The methods of preparing of colloidal solutions. Their properties.

1. LECTURE Disperse systems. The methods of preparing of colloidal solutions. Their properties. ass. prof. Iryna R. Bekus

2. Plan 1. The main concepts and determination 2. Classification of the dispersed systems 3. Preparation methods of the dispersed systems 4. Purification methods of the dispersedsystems

3. Dispersed Systems • A kinetically stable mixture of one phase in another largely immiscible phase. Usually at least one length scale is in the colloidal range.

4. Dispersed Systems Dispersed phase Continuous phase Interface

5. Classification of dispersed system in agreement with particles scale Molecular dispersions is a true solutions of a solute phase in a solvent. The dispersed phase (solute) is in form of separate molecules homogeneously distributed throughout the dispersion medium(solvent). The molecule size is less than 1 nm (4*10-8 inch). [The examples : air (a molecular mixture of Oxygen, Nitrogen and some other gases), electrolytes (aqueous solutions of salts)]. Colloids are micro-heterogeneous dispersed systems, in which the size of the dispersed phase particles is within the range 1 - 1000 nm (4*10-8 - 4*10-5 inch). The colloids phases can not be separated under gravity, centrifugal or other forces. Dispersed phase of colloids may be separated from the dispersion medium by micro-filtration. The examples of colloids: milk (emulsion of fat and some other substances in water), fog (aerosol of water micro-droplets in air), opal (colloidal silica), Silica aerogel monolith, Alumina aerogel monolith]. Coarse dispersions (suspensions) are heterogeneous dispersed systems, in which the dispersed phase particles are larger than 1000 nm (4*10-5“). Coarse dispersions are characterized by relatively fast sedimentation of the dispersed phase caused by gravity or other forces. Dispersed phase of coarse dispersions may be easily separated from the continuous phase by filtration.

6. Classification of the dispersed systems according to the particle size Molecular-dispersion <10-9м Ultramicroheterogeneous 10-7 ÷ 10-9 м Microheterogeneous 10-4 ÷ 10-7 м Coarse-dispersion >10-4 м

8. http://www.youtube.com/watch?v=q96ljVMHYLo

9. Sols and emulsions are the most important types of colloidal dispersion.

11. Fog Fog

12. Classification of dispersed systems according to the particle-dispersion mediuminteraction Lyophilic (liquid-loving) good interaction of dispersed particle with dispersed medium emulsionan a water-in-oil Lyophobic (liquid-hating) (no any interaction of dispersed particle with dispersed medium)emulsionan oil-inwater

13. Types of Emulsion A fine dispersion of one liquid in a second, largely immiscible liquid. In foods the liquids are inevitably oil and an aqueous solution. mm Water Oil Emulsions are an example of colloids composed of tiny particles suspended in another immiscible (unmixable) material. Oil-in-water emulsion Water-in-oil emulsion

15. Classification of dispersed systems according to the particle-particleinteraction Free dispersion or no sharp line of demarcation (particles moving free) sols Not free dispersion or sharp line of demarcation (particle-particleinteraction between themself) gels, foams

16. Colloidal particlescan be classified according to shape as corpuscular,laminar or linear Manycolloidal systems do, in fact, contain spherical ornearly sphericalparticles. Emulsions, latexes, liquid aerosols, etc., contain sphericalparticles. Certain protein molecules are approximately spherical. Thecrystallite particles in dispersions such as gold and silver iodide solsare sufficiently symmetrical to behave like spheres.

17. Colloidal solution Colloidal solutions have dispersed phase particle, which size from 10-9 to 10-7m or 1 nm to 100 nm.

18. http://www.youtube.com/watch?v=-jZyqqN4uqc&feature=related

19. Dispersion These methods involve the breaking of the bigger particles to colloidal size.

20. Dispersion method of the preparation of colloid solution

21. Peptization - is a process of passing of a precipitate into colloidal particles on adding suitable electrolyte. The electrolyte added is called peptizing agent.

22. Condensation methods of the preparation of the colloidal solutions. It bases on the appearing of a new phase in the homogenius phase according to the joining of molecules, atoms, ions.

23. Dialysis • The process of separating the particles of colloids from those of crystalloids by diffusion of the mixture through semipermeable membrane (а parchment or an animal membrane) is known as dialysis. • The above process can be quickened if an electric field is applied around the membrane (the process is then called Electrodialysis).

24. Dialysis

25. A further modification of dialysis is the technique of electrodialysis

26. Electro-dialyser

27. The most important application of dialysis is in the purification of blood in the artificial kidney

28. Hemodialysis In hemodialysis, the patient's blood is pumped through the blood compartment of a dialyzer, exposing it to a partially permeable membrane.

29. Ultrafiltration:а) vacuum; b) preassure c) gel permeation chromatography а) b)

30. Diffusion is the tendency for molecules tomigrate from a region ofhigh concentration to a region of lowerconcentration and is a directresult of Brownian motion.

31. Properties 1. Physical Properties • Heterogeneous character • Stability • Filterability • Visibility 2. Colligative properties - osmotic pressure 3. Mechanical properties – Brownian movement 4. Optical properties – Tyndall affect 5. Electrical properties

33. Osmotic pressureof colloid solutions: 1. Osmotic pressure is very low:

34. http://www.youtube.com/watch?v=k5HMVIb4J7A&NR=1

35. Kineticstability • А major source of kinetic stability of colloids is the existence of an electric charge on the surfaces of the particles. On the account of this charge, ions of opposite charge tend to cluster nearby, and an ionic atmosphere is formed.

36. The movement of colloidal particles under the influence of an electric field is called electrophoresis or cataphoresis. а) Before electrophoresis (b) After electrophoresis

37. Flocculation (coagulation) Aggregation of the particles arising from the stabilizing effect of this secondary minimum is called flocculation.

38. Hardy-Schulze Law • Greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation.

39. Sedimentation • In а gravitational field, heavy particles settle towards the foot of а column of solution by the process called sedimentation.

40. Thank you for attention