Colloid chemistry презентация

disperse systems

- a systems, where interaction of the particles of the dispersed phase with the solvent is highly expressed.
Lyophobic - dispersion phase interacts weakly with the dispersion medium.

Hydrophilic (a) and hydrophobic (b) surface in a three phase system - water - solid - air; 1 - Water 2; - Solid; 3 - air; a - wetting angle.

IONS
OF ELECTROLYTE ALSO USED FOR MORE SUSTAINABLE
DISPERSE SYSTEMS

The mechanism of action is in the formation on
the interface environment-particle adsorption
layers.

Intensification of dispersion

used to obtain highly dispersed systems;
do not require the cost of external work;
emergence of a new phase occurs at a supersaturation environment.

Condensation methods

stabilizer (DEL).

consists of 2 parts:

Micella - colloidal structural unit, surrounded by an electric double layer.

Intermicellar fluid - the dispersion medium, separating the micelles, where the electrolytes, non-electrolytes and surfactants are soluted.

approximation, because it has no specific composition.

forming a so-called adsorption layer counterions; nucleus together with adsorbed thereon are called counterions colloidal particles or granules. The remaining counter, the number of which is determined on the basis of the rules of electrical micelles constitute a diffuse layer of counterions; counterions adsorption and diffusion layers are in a state of dynamic equilibrium adsorption - desorption.

Charged core attracts ions from the solution with the opposite charge - counterions; interfacial electrical double layer is formed.

I

With an excess of one reactant microchip adsorbs its ions, which do not form a precipitate.
As a result of this microchip acquires a charge, ions, informing him that the charge potential-called, and he charged crystal - core micelles.

obtained by the reaction:
АgNО3(s) + КI(s) = АgI(cryst.) + KNO3(s)

а) nАgNО3 = nКI : surface sediment is not charged;
б) nАgNO3 > nКI : в) nАgNО3 < nКI :
excess АgNO3 ⬄ Аg+ + NО3- excess КI ⬄ К+ + I-

АgI + АgI -
+ -
+ -

2H2O

Micelle structure :

↓ + 3HCl

Micelle structure :

low molecular weight impurities sols through a semipermeable membrane.

Methods of cleaning of disperse systems

begin to move: positive –
The cathode to the anode and the negative

Low molecular weight impurities destroy colloidal systems.
Electrodialysis - dialysis, accelerated by an external electric field.

Methods for cleaning of disperse systems

electrodialysis under pressure (hemodialysis).

Methods for cleaning of disperse systems

true solutions. Weighted particles in the solution are in constant random thermal motion.

as a result the average kinetic energy is set, same for all particles.

volume of solution or gas under the influence of thermal motion.
Einstein studied the Brownian motion, he established the diffusion coefficient - D connection with an average shift:

Einstein showed that the diffusion coefficient D is related to the size of the diffusing particles equation:

r – the radius of the spherical particles whose size is much larger than the size of the solvent molecules

amount, it is difficult reproducible experiments.
Osmotic pressure in colloidal systems is inversely proportional to the cube of the particle radius:

– osmotic pressure in a total sols same substances with different particle dispersion

of dispersed particles in a liquid or gaseous medium under the influence of gravity.
Emergence of particles is called reverse sedimentation.
Sedimentation rate of the particles obeys the law Stokes :

ρ, ρ0 - and medium density particles;
ή viscosity of the medium;
r - radius;
g- acceleration of gravity

If the difference ρ-ρ0 has the sign «-» medium particles are lighter and float

size and mass of the particles is not enough force gravity.
Russian scientist AV Dumanskiy (1912) proposed to expose colloidal systems centrifugation.
Swedberg (1923) developed a special centrifuge with great speed, called the ultracentrifuge.

the acceleration of gravity 105.
Modern ultracentrifuge - complex apparatus central part rotor of which (with speed 20-60000 rev / min and up).

colloidal systems. The light is scattered in all directions.
This phenomenon was observed Faraday (1857) in the study of gold sol. The phenomenon Tyndall in 1868.
Through pure liquids and molecular solutions light just passes.
Through colloidal dispersions light ray meeting on the way a particle is not reflected, as if it skirts, and rejected several changes its direction (diffraction).

Faraday

Tyndall

light ray path it is visible when viewed side as a luminous cone - Tyndall cone.

the potential jump at the interface of the two phases plays an important role in many phenomena important for theory and practice .
These include: the electrode processes , electrocapillary and electrokinetic phenomena , phenomena associated with the electrostatic interaction of colloidal particles , largely determine the stability of the dispersed system .
All these phenomena are interconnected through DEL , called Electrosurface .
There are three possible mechanisms for the formation of DEL :
Due to the transition of electrons or ions from one phase to another ( 1st variant );
As a result of the selective adsorption of ions in the electrolyte interphase layer ( 2nd variant );
As a result of the orientation of the polar molecules conjugated phases in their interaction ( third variant ) .

ions, which are located in the crystal lattice as a result of interaction with the dipoles of water will go into solution.

by reaction between AgNO3 and KI at AgI microcrystals adsorbed ions (Ag +, I-). If an excess of silver nitrate, the silver ions are adsorbed. When this solid phase is positively charged (variant b). Excess anions NO3-ions are attracted to the Ag +

Salt

Salt

the interface in the presence of metal ions. At the same potential-anions are polar (example) fatty acids

metal ions

fatty acid

solid surface

and developed in the works of Helmholtz (1879).
DEL theory was developed in the works of scientists of the USSR A.N. Frumkin and B.V. Deryagin.
The first theory was the theory of the structure of DEL Helmholtz:
DEL consists of two flat charges located at the molecular distance from one another and interact with each other only by electrostatic forces of attraction.

of forces acting in opposite directions: the electrostatic forces of attraction to the surface and forces the thermal motion of the ions.

The theory introduces the concept of the diffusion layer, the ions are treated as point charges that do not have their own size.

ions are included in the solid phase, form the inner lining of the double layer, ions of opposite sign, i.e. counterions forming an outer lining, wherein the counterions part is in direct contact with ions of the solid phase, forming a dense layer, and another part is counterions diffused layer.

of which is characterized by the value potential. The potential change in DEL depending on the distance shown in pic. In this case the potential drop within the dense layer is linear, and in the diffusion layer - exponentially.

Potential at the interface Δ and potential so-called plane as close as possible (within a distance of the order of molecular dimensions δ) φ0 belong to the category of almost immeasurable value.

On a solid surface charge arises, called φ-potential. Sign φ-potential coincides with the sign of the charge and its potentsal-forming ions calculated by the Nernst equation. φ-potential is the work of a single transfer (elementary) charge from infinity far place to the surface of the solution volume of the solid phase

sliding phases determined experimentally by various methods. ζ-potential can be represented as the work necessary for the transfer of charge from the unit element of an infinitely distant volume of solution on the sliding surface. ζ-potential sign coincides with φ-potential

ξ = η*U0/ε0*ε*E

U0 – velocity of the fluid, ε0 – constant, ε - dielectric permittivity a liquid, E – the electric field strength,
ξ - potential, η- fluid viscosity.

phases under the influence of the potential difference

Electrokinetic phenomena 2nd kind - the emergence of a potential difference due to the forced displacement relative phases

Electrophoresis - motion of dispersed particles in an electric field

Electroosmosis - the movement of the dispersed medium in the electric field of the dispersed phase relative to the stationary

Potential sedimentation - the emergence of a potential difference in the motion of particles in a stationary liquid

Potential flow - the emergence of a potential difference in fluid motion relative to a stationary solid surface

In 1808 a professor at Moscow University F.F. Reuss in studies of water electrolysis.

Reiss put two experiments. In the first he used a U-shaped tube, in the second dipped two glass tubes in the clay. By passing a DC clay particles move toward the positive electrode. Electrophoresis mechanism is that under the influence of an electric field ions double layer is torn at the boundary of the slip, the particle acquires a charge, and moves to the oppositely charged electrode, counter ions move in the reverse direction.

when electroosmosis directly proportional to the electric field E and the dielectric constant ε of the dispersion medium and inversely proportional to the medium viscosity η. Particle velocity of the dispersed phase electrophoresis U related to the value ζ-potential of the equation Helmholtz-Smoluchowski

U0 = ε0*ε*E*ξ/η

Electrophoresis allows to deliver the drug directly to the affected area and gradually establish there a sufficient concentration.

U-shaped glass tube with powdered quartz, poured water, loaded electrodes and passed the direct current through. After some time, the water level in the knee with increased negative electrode, and the second knee - dropped. This phenomenon is called electroosmosis.

phenomenon of the potential difference in the dispersion medium motion relative to the fixed dispersion phase.

Sedimentation potential (Dorn effect) - the emergence of a potential difference in induced motion of the dispersed phase relative to the fixed dispersion medium.

chemistry

stability of disperse systems are divided into two types: Kinetic stability - property dispersed particles held in suspension without collapsing.

Aggregate stability - the ability of the dispersed phase provide blocking resistance and thus maintain a certain degree of dispersion of this phase as a whole.

larger aggregates with consequent loss of kinetic stability, can be caused by:


introduction of electrolytes;
heating or freezing of the dispersed system;
mechanical action;
high-frequency oscillations;
ultracentrifugation.

the sol.

Usually charge sign: sol coagulation that causes ion electrolyte sign of the charge which is opposite to the charge of the colloidal particle. This ion-ion called coagulator.

Each electrolyte in relation to the colloidal solution has a threshold of coagulation.

as protective colloids. In case of violation of protein metabolism shell flat out, which leads to the top of their adhesion. With further development of the disease protein shell disappear completely.