Motion of heavy particles settle down in response to an exter nal force such as gravity , centrifugal force or electric force
Rate of sedimentation depends on the strength of the field, masses and shapes of the particles
Sedimentation Theory(a) Gravitational sedimentation(b) Centrifugal sedimentation
-Sedimentation velocity-Sedimentation Equilibrium
2.2 Kinetic property
Sedimentation
(a) Gravitational Sedimentation
m
F1
F2Fb (buoyancy)
Fg (gravity)
(a) Gravitational Sedimentation
m
F1 = fVg
F2 = mg(1 - 2/1)
At equilibrium :fVg = mg(1 - 2/1)
m = fVg
g(1 - 2/1)M = fNAVg
g(1 - 2/1)1 = density of particle2 = density of medium
F1
F2
(b) Centrifugal Sedimentation
•sedimentation velocity•sedimentation equilibrium
= angular velocity (rpm)
b.1 Sedimentation velocity
an analytical ultracentrifugation method that measures the rate at which molecules move in response to centrifugal force generated in a centrifuge .This sedimentation rate provides information about both the molecular mass and the shape of molecules .In some cases this technique can also measure diffusion coefficients (D).
b.1 Sedimentation velocity
F1
F1 = fV = f(dr/dt) F2 = m2r (1 - 2/1)
At equilibrium :f(dr/dt) = m 2r (1 - 2/1)
M = sfNA = sRT
(1 - 2/1) D(1 - 2/1)
S = (dr/dt) = m(1 - 2/1) 2r f
r
F2
s = sedimentation coefficient ( Svedberg,1Sv=10-13 s)
~ 80,000 rpm
b.2 Sedimentation equlibrium
M = 2RT ln (C2/C1) (1 - 2/1) 2 (r2
2-r12)
~ 10,000 rpm
=
Assignment-3
GGrouproup P PresentationresentationCComparing to omparing to sedimentationsedimentation
G1 : G1 : precipitation,precipitation, aggregationaggregation G2 : G2 : coagulation,coagulation, flocculationflocculation
(10 students per group)
(5 min)
3.3. O Opticalptical p property roperty
A colloidal system contains particles that affect a light beam by scattering and absorption .
If the particles are of a size comparable to the wavelength () of light or larger, they scatter or absorb light independently .
The same thing happens if they are separated by distances comparable to or greater than the wavelength () of light .
3.3. C Commonommon O Opticalptical pphenomena henomena
the interaction of light from the sun or moon with the atmosphere, clouds, water, or dust and other particulates
Assignment-4
GGroup roup PPresentationresentationG3 : Rayleigh Scattering G3 : Rayleigh Scattering G4 : RamanG4 : Raman ScatteringScatteringG5 : Mie ScatteringG5 : Mie ScatteringG6 : Bragg ScatteringG6 : Bragg Scattering
(10 students per group)
(5 min)
