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)