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2.2 Kinetic property Sedimentation • Motion of heavy particles settle down in response to an external 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
(a)Gravitational Sedimentation Fg(gravity) F1 m Fb (buoyancy) F2
(a) Gravitational Sedimentation F1 = fVg F2 = mg(1 - 2/1) F1 m At equilibrium : fVg = mg(1 - 2/1) m = fVg g(1 - 2/1) F2 M = fNAVg g(1 - 2/1) 1 = density of particle 2= density of medium
(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 = fV = f(dr/dt) F2 = m2r (1 - 2/1) F1 r At equilibrium : f(dr/dt) = m 2r (1 - 2/1) ~80,000 rpm F2 S = (dr/dt) = m(1 - 2/1) 2rf s = sedimentation coefficient (Svedberg, 1Sv=10-13 s) M = sfNA = sRT (1 - 2/1) D(1 - 2/1)
b.2 Sedimentation equlibrium = M = 2RT ln (C2/C1) (1 - 2/1) 2 (r22-r12) ~10,000 rpm
Assignment-3 (10 students per group) Group PresentationComparing to sedimentation G1 : precipitation,aggregation G2 : coagulation,flocculation (5 min)
3. Optical property 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 distancescomparable to or greater than the wavelength () of light.
3. Common Optical phenomena the interaction of light from the sun or moon with the atmosphere, clouds, water, or dust and other particulates
Assignment-4 (10 students per group) Group PresentationG3 : Rayleigh Scattering G4 : RamanScatteringG5 : Mie ScatteringG6 : Bragg Scattering (5 min)