Disperse%20and%20colloidal%20systems

1
Disperse and colloidal systems

• Jana Novotná

2
Types of disperse systems

• The term "Disperse System" refers to a system in
  which one substance (the dispersed phase) is
  distributed, in discrete units, throughout a
  second substance (the continuous phase or
  vehicle).
• Each phase can exist in solid, liquid, or gaseous
  state .

3
Types of disperse systems
True solution lt 1 nm
Heterogenous dispersion gt 500 (1000) nm
Colloid dispersion 1 500 (1000) nm
homogenous systems, salt, acid and base solutions
microheterogenous system (plasma, macromolecular
solutions)
heterogenous systems (blood, milk)
coagulation (floculation)
condensation, aggregation
4
Classification of desperse systems
Medium/Phase Dispersed phase Gas
Liquid Solid Gas None Liquid
aerosol Solid aerosol (All gases are
mutually (fog, hair sprays) (smoke cloud,
air miscible) particles)
Liquid Foam Emulsion Sol
(whipped cream, (milk (blood
shaving cream) mayonnaise) pigmented
ink) Solid Solid foam Gel
Solid sol (aerogel, pumice (agar,
gelatine (jewel, gemstone)
polystyrene foam) jelly, opal)
Continuous medium
5
Properties of disperse systems
Heterogenous dispersion Colloid dispersion True solution
Pass through membranes ? Semipermeabil does not pass
Visibility of particles Eye, optical microscope Electron microscope ?
Sedimentation Ultracentrifu- gation ?
Thermal motion Small Middle High
6
Properties of disperse systems
Heterogenous dispersion Colloid dispersion True solution
Colligative properties ? Small High
Difuse ? Slow Fast
Optical properties Frequently opaque Opalescent (Tyndall effect) Transparent
Separability Paper filters Membrane filters None
7
Heterogenous (rough) dispersion

• Suspension - heterogeneous fluid containing solid
  particles that are sufficiently large for
  sedimentation.
• Particle size is gt 1 mm
• Dispersion is made by mechanical agitation (sand
  in the water).
• Aerosol - a suspension of liquid droplets or a
  suspension of fine solid particles in a gas.
• Example smoke, air pollution, smog etc.

8
Heterogenous (rough) dispersion

• Emulsion - a mixture of two or more immiscible
  liquids
• one liquid (the dispersed phase) is dispersed in
  the other (the continuous phase).
• Prepared by shaking oil/water (milk), water/
  oil (butter).

9
Colloids

• Particle size 1 1000 nm.
• Particles have very large surface area
• Homogenous colloidal system - lyophilic
  dispersion.
• Heterogenic colloidal system lyophobic
  dispersion

10
Properties of colloid solutions

• Particles are visible only by ultramicroskop or
  electron microskop Brown motion.
• They do not sedimentate, pass through common
  filters ( but not through semipermeable
  membrane).
• Dispersion of passing light (Tyndall efect).
• Produce osmotic pressure.

11
Properties of colloid solutions

• Colloids are everywhere
• In the human body
• Washing powder, soup, tooth paste, etc.
• Many foods ( yogurt, butter, milk)
• Nanotechnologies are based on chemistry of
  colloids

12
Lyophilic colloids

• Lyophilic particles are mixed with the suitable
  solvent. Particles have high affinity to the
  solvent.
• High force of attraction exists between colloidal
  particles and liquid.
• This result in formation of very stable solution
  called lyophilic sol.
• Attraction forces (solvate cover) stabilize
  lyophilic colloid, defense their clustering to
  the larger complexes
• Cells contain solution of lyophilic colloids

13
(No Transcript)
14
Lyophobic colloid

• Colloid particles do not have affinity to the
  molecules of solvent
• Mostly complexes of inorganic particles which do
  not have affinity to the solvent
• They are prepared by artificial dispersion -
  Fe(OH)3, As2S3

15
Negative charge of S2- or HS- is compensated by
opposite charge from the (H).
16
Emulsions

• Stable coloidal system in which both phases are
  liquids (water and oil)
• Miscible liquid form a solution
• Lyophobic colloids form an emulsion
• Emulsifying agent substance require to form a
  stable emulsion
• Emulsifyin agent is surface-active, i.e.it reduce
  the surface tension (soap, many other detergents.

17
Solutions

• A solution is a homogenous mixture composed of
  two or more substances.
• A solute is dissolved in another substance, known
  as a solvent.
• Types of solutions
• Solvent is gas (mixture of different gases)
• Solvent is liquid
• Gas in liquid (water solution of HCl)
• Liquid in liquid (H2SO4 in the water)
• Solid in liquid (glucose , NaCl in the water)
• Solvent is solid alloys like bronze (Cu and Sn)

18
Solubility

• The ability of one compound to dissolve in
  another compound
• Miscible liquids - liquid is able to completely
  dissolve in another liquid (ethanol, water).
• The solubility of a given solute in a given
  solvent typically depends on temperature
• Solubility of ionic compounds - there is a limit
  to how much salt can be dissolved in a given
  volume of water

19
Solubility
20
Dissolving substances in water

• No-electrolytes do not interact with the solvent
  (oxygen, sucrose).
• Electrolytes interact with molecules of the
  solvent ? dissociate, ionize
• The ions are then surrounded by solvent molecules
  (H2O).
• Hydrated ions then arise.

21
Diffusion

• Diffusion is the spontaneous mixing of two
  substances with different concentrations over a
  semi-permeable membrane.
• The reason of diffusion is the thermal motion of
  molecules.
• The bulk of diffusion is characterized by
  diffusion coefficient (D)
• D amount of diffusing substance per time unit
  through 1 cm3, at a concentration gradient equal
  to 1 .
• Concentration gradient is
• D Dc/l
• c concentration, l - membrane thickness

22
Osmosis

• Two solutions of different concentrations are
  separated by semi-permeable membrane
• Equilibrium occurs
• when the membrane is permeable - the substance is
  distributed equally
• when the membrane is semi-permeable the solvent
  moves
• Osmotic pressure - the pressure applied against
  the transfer of solvents through the membrane

23
Osmotic pressurs

• Proportional to the concentration of substance
  dissolved particles (regardless of size).
• Ionizable substances - participates in the
  osmotic pressure alone
• p iRTc
• i number of ionized particles, c
  concentration in mol.l-1, T temperature in
  Kelvine, R gas constant
• The values of the coefficient i depends on the
  nature of the substance and its concentration
• non-dissociated particles ? i 1
• univalent salts (KCl, NaCl, KNO3) ? i 2
• uni-divalent salts (K2(SO)4, CaCl2) ? i 3
• uni-trivalent salts (AlCl3, K3Fe(CN)6) ? i 4
• Osmotic pressure in colloidal dispersions
  oncotic pressure

24
Osmotic pressurs

• Osmotic pressure is an important factor affecting
  cells.
• Osmoregulation is the homeostasis mechanism of an
  organism to reach balance in osmotic pressure.
• hypertonicity is the presence of a solution that
  causes cells to shrink.
• hypotonicity is the presence of a solution that
  causes cells to swell.
• isotonicity is the presence of a solution that
  produces no change in cell volume.