Small effort to sum up the properties of colloids.

1. Praveen Suthar & naagendra
dewasi
B.pharm student
E mail:
praveensuthar123@gmail.com

2. TYNDALL EFFECT
When a beam of light falls at right angles to the line of view
through a solution, the solution appears to be luminescent
and due to scattering of light the path becomes visible
strong in lyphobic colloids while in lyophilic colloids it is
quite weak

3. Explanation
The Tyndall Effect is due to scattering of light by
colloidal particles. The colloidal particles first absorb
light and then a part of absorbed light is scattered
from the surface of the colloidal particles. Maximum
scattering intensity being in a plane at right angles to
plane of incident light, the path becomes visible when
seen from that direction. The particles of pure solvents
or true solution are too small to scatter light.

4. Light scattering
When a beam of light is directed at a colloidal
solution or dispersion, some of the light may be
absorbed (colour is produced when light of certain
wavelengths is selectively absorbed), some is
scattered and the remainder is transmitted
undisturbed through the sample.

5. Dark-field microscopy-the ultramicroscope
Dark-field illumination is a particularly useful technique for
detecting the presence of, counting and investigating the
motion of suspended colloidal particles. It is obtained by
arranging the illumination system of an ordinary microscope
so that light does not enter the objective unless scattered by
the sample under investigation.
Lyophobic particles as small as 5-10 nm can be made indirectly
visible in this way.
The two principal techniques of dark-field illumination are the
slit and the cardioid methods.
1) In the slit ultramicroscope of Siedentopf and Zsigmondy
(1903) the sample is illuminated from the side by an intense
narrow beam of light from a carbon-arc source

6. The transmission electron microscope
To increase the resolving power of a microscope so that
matter of colloidal (and smaller) dimensions may be observed
directly, the wavelength of the radiation used must be
reduced considerably below that of visible light. Electron
beams can be produced with wavelengths of the order of
0.01 nm and focused by electric or magnetic fields, which act
as the equivalent of lenses. The resolution of an electron
microscope is limited not so much by wavelength as by the
technical
difficulties of stabilising high-tension supplies and correcting
lens aberrations.
The useful range of the transmission electron
microscope forparticle size measurement is c. 1 nm-5
μm diameter.

8. There are continuous collisions between the
colloidal particles and molecules of dispersion
medium which are in constant motion and passes
kinetic energy to colloidal particles by striking it
from all sides. This results into zigzag movement
of colloidal particles. This zigzag movement of
colloidal particles is known as Brownian
movement
BROWNIAN MOTION

13. Electrical properties
of colloids

14. Zeta potential (ζ-potential)
Zeta potential
is the
electrokinetic
potential
difference
between
the dispersion
medium and
the stationary
layer of fluid
attached to
the dispersed
particle.
Diagram showing the ionic concentration
and potential difference as a function of
distance from the charged surface of a
particle suspended in a dispersion
medium.

15. The significance of zeta potential is that its value
can be related to the stability of colloidal
dispersions (e.g., a multivitamin syrup).
The zeta potential indicates the degree of
repulsion between adjacent, similarly charged
particles (the vitamins) in a dispersion.
For molecules and particles that are small
enough, a high zeta potential will confer stability,
i.e., the solution or dispersion will resist
aggregation. When the potential is low, attraction
exceeds repulsion and the dispersion will break and
flocculate.

16. Electrophoresis (or Cataphoresis):
Since the colloidal particles are electrically charged (+ or -)with
respect to the dispersion medium, hence on passing electric
current through colloidal solution the charged particles move
towards oppositely charged electrodes and get discharged to
give precipitate. So, this migration of colloidal particles under
the influence of electric field is called electrophoresis.

17. Electro-osmosis:
molecules of dispersion medium are allowed to move under
influence of electric field
Coagulation or flocculation:
which involves coming together of colloidal particles so as to
change into large sized particles which ultimately settle as a
precipitate or float on surface.it is generally brought about by
addition of electrolytes
GOLD NUMBER:
Covering up of lyophobic particles by lyophilic particles is known
as its protective action and such colloids are called protective
colloids.
Gold number is defined as amount of
protective sol that will prevent the
coagulation of 10 ml of a gold solution
on the addition of 1 ml of 10% NaCl
solution.

18. THANK
YOU