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S edimentation T heory (a) Gravitational sedimentation (b) Centrifugal sedimentation

2.2 K inetic p roperty. S edimentation. 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. S edimentation T heory

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S edimentation T heory (a) Gravitational sedimentation (b) Centrifugal sedimentation

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  1. 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

  2. (a)Gravitational Sedimentation Fg(gravity) F1 m Fb (buoyancy) F2

  3. (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

  4. (b) Centrifugal Sedimentation • sedimentation velocity • sedimentation equilibrium  = angular velocity (rpm)

  5. 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).

  6. b.1 Sedimentation velocity F1 = fV = f(dr/dt) F2 = m2r (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)

  7. b.2 Sedimentation equlibrium = M = 2RT ln (C2/C1) (1 - 2/1) 2 (r22-r12)  ~10,000 rpm

  8. Assignment-3 (10 students per group) Group PresentationComparing to sedimentation G1 : precipitation,aggregation G2 : coagulation,flocculation (5 min)

  9. 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.

  10. 3. Common Optical phenomena the interaction of light from the sun or moon with the atmosphere, clouds, water, or dust and other particulates

  11. Assignment-4 (10 students per group) Group PresentationG3 : Rayleigh Scattering G4 : RamanScatteringG5 : Mie ScatteringG6 : Bragg Scattering (5 min)

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