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

properties. Physical-chemical properties of biopolymer solutions.

ass. prof. Yeugenia B. Dmukhalskaass. prof. Yeugenia B. Dmukhalska

LECTURE 5LECTURE 5

Plan1. The main concepts and determination2. Classification of the dispersed systems 3. Preparation methods of the dispersed

systems 4. Purification methods of the dispersed

systems

Classification of the dispersed systems according to the

particle size

Ultramicroheterogeneous10-7 ÷ 10-9 м

Microheterogeneous10-4 ÷ 10-7 м

Coarse-dispersion>10-4 м

Sols and emulsions are by far the most Sols and emulsions are by far the most important types of colloidalimportant types of colloidal dispersion.dispersion.

Classification of dispersed systems according to the particle-dispersion medium

interaction

Lyophilic (liquid-loving)

good interaction of dispersed particle with dispersed medium

emulsion and a water-in-oil

Lyophobic (liquid-

hating)

(no any interaction of dispersed particle with dispersed medium)emulsion an oil-in water

Classification of dispersed systems according to the particle-particle interaction

Free dispersion or Free dispersion or no no sharp line of sharp line of demarcation demarcation (particles moving free)

sols

Not free dispersion or Not free dispersion or sharp line of sharp line of demarcationdemarcation

(particle-particle interaction between

themself)

gels, foams

CColloidal particlesolloidal particles can be classified can be classified according to shape as according to shape as

corpuscular,corpuscular, laminar laminar or or linearlinearMManyany colloidal systems do, in fact, colloidal systems do, in fact, contain spherical orcontain spherical or nearly sphericalnearly spherical particles. Emulsions, latexes, liquid particles. Emulsions, latexes, liquid aerosols, etc., contain sphericalaerosols, etc., contain spherical particles. Certain protein molecules are particles. Certain protein molecules are approximately spherical. Theapproximately spherical. The crystallite crystallite particles in dispersions such as gold particles in dispersions such as gold and silver iodide solsand silver iodide sols are sufficiently are sufficiently symmetrical to behave like spheres.symmetrical to behave like spheres.

Some model representations for Some model representations for non-spherical particlesnon-spherical particles

Dispersion method of the preparation of colloid solution

Mechanical

Using crusher, mill, mixer

Electrical

using the instruments for electrolytic spraying

Acoustic

using ultrasound

PeptisationPeptisation – chemical dispergation is transfering the sediment in the state of

sol

BallBall (а) (а) andand colloidcolloid ( (bb) ) mill

а)а) bb))

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

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.

Physical Physical Condensation from a pair, the

substitution of a poor solvent

ChemicalChemicalFeCI3+3H2O → Fe(OH)3 +3HCl

AgNO3 + KCl → AgCl + KNO3

2H2S + SO2 → 3S + 2H2O

Ag2O + H2 → 2Ag + H 2O

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 Electro-dialysis).

Dialysis

A further modification of dialysis is the technique of electrodialysis

Electro-dialyser

The most important application of dialysis is in the purification of blood in

the artificial kidney

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

а) b)

Molecular-kinetic and optical properties of the colloidal systems

Brownian motion The motion of

colloidal particle in dispersed medium

Direction of the particle

AverageBrownian displacement

Diffusion

is the tendency for molecules to migrate from a region of high concentration to a region of lower concentration and is a direct

result of Brownian motion.

Osmotic pressureof colloid solutions:

1. Osmotic pressure is very low:

aN

RT

V

2. Osmotic pressure is inversely proportional to the cube of radius of particles and is directly proportional to raise to the cube (third) power of its dispersion in the same dispersed medium:

32

31

31

32

2

1

D

D

r

r

Properties1. Physical Properties

• Heterogeneous character• Stability• Filterability • Visibility 2. Colligative properties - osmotic pressure3. Mechanical properties – Brownian movement 4. Optical properties – Tyndall affect 5. Electrical properties

Kinetic stability• 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.

On placing а colloidal solution under the influence of an electric field, the particles of the dispersion medium move

towards oppositely charged electrode, provided the colloidal particles is called electro-osmosis.

The movement of colloidal particles under the influence of an electric field is called

electrophoresis or cataphoresis.

а) Before electrophoresis

(b) After electrophoresis

Flocculation (coagulation)

Aggregation of the particles arising from the stabilizing effect of this secondary minimum is called flocculation.

Hardy-Schulze Law

• Greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation.

Sedimentation

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

Physical-chemical properties of biopolymers.

The high-molecular compounds (HMC) are compounds – polymers, which have 10000 – 10000000 Da (Dalton – unit of atomic mass) molecular mass.

А polymer is а large molecule formed by the covalent bonding of repeating smaller molecules.

For example natural macromolecules: polysaccharides: glycogen, cellulose, starch, proteins, nucleic acids: RNA, DNA.

Biological role of polymers• Biopolymers, have a lot functions:

• Catalytic effect– enzymes;

• As regulators – hormones;• is the storage and transfer of genetic information.

(DNA);• Storage energy (Starch, glycogen);

• Protection - immunoglobulin;

• Structural (collagen, keratins, fibril).

CLASSIFICATION HMC • Polymers are classified by different possible:• Classification by source;• Classification by structure;• Classification by synthesis;• Classification by molecular forces.

Classification by source

• Natural (nucleic acids, polysaccharides, protein, natural rubber (polyisoprene));

• Synthetic (polyethelene, teflon, polyvinilchloride, polystyrene).

Classification by structureLinear polymers. In these polymers, the

monomers are joined together to form long straight chains of polymer molecules. Because of the close packing of polymer chains, linear polymers have high melting point, high densities and high tensile (pulling) strength.

Branched chain polymers. In these polymers, the monomer units not only combine to produce the linear chain (called the main chain) but also form branches along the main chain

Three-dimensional network polymers. In these polymers, the initially formed linear polymer chains are joined together to form а three-dimensional network structure.These polymers are also called cross-linked polymers

Classification by molecule form

• Globular. • Fibril.

Classification by nature atoms, which are in molecule of polymer

• Carbon contain polymers

• Hetero polymers

• Element organic

• Inorganic

Synthesis of polymers• Addition

polymerization occurs when unsaturated monomers react to form а polymer. It is а specific type of addition reaction.

Condensation Condensation polymers are formed by the head-to-tail joining of monomer units. This is usually accompanied by the loss of а small molecule, such as water.

Properties • Properties HMC solution, which same as true solutions:

• Solutions of high-molecular compounds are stable as molecular solutions;

• Solutions of high-molecular compounds are convertible. If high-molecular compound was solved that the molecular solution will be farmed. And if this solution to strip to dryness, so high-molecular compound was stat, which can solve again.

• Between high-molecular compound and solvent has not boundary.

Properties HMC solution, which same as colloidal solutions:Size of disperse phase in solutions of high-molecular compounds are same as in colloidal solutions (10-7 - 10-9 m);High-molecular compounds can not permeate through semipermeable membrane;High-molecular compounds slowly are diffused in solutions.Specific properties HMC solution:For solutions of high-molecular compounds are characteristic the swelling and high viscosity

• Swelling it is process solubility high-molecular compound in solvent.

• Swilling degree (α):

• α = (m – m0)/m0 = mp/m0

• or α = (V – V0)/ V0 = VP / V0

• Where: m0 and V0 – mass or volume polymer before swilling;

• m and V – mass or volume polymer after swilling;

• mp, Vp – mass or volume of solvent, which is absorbed polymer.

• Some time used mass-volume swilling degree: α= (V0 – V)/ m = cм3/g

• or α = (V0 – V)100%/m