BIOL 2020 Lecture Notes - Lecture 6: Angular Velocity, Centrifugal Force, Viscosity
20 Apr 2020
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4. sedimentation method density & particle size affect how fast particle can fall & distance. Gravity: 10um- 1000um; centrifugal: 0. 1-500um, strokes diameter, weighted average diameter. One method where you put particles dispersed in medium w/viscosity and density. Equivalent diameter from method is stroke diameter equivalent to sedimentation speed diameter. Wet: gravitational method: 10um-1000um, gravitational takes long. Velocity is proportional to square of strokes diameter, different in density of particles and density of medium and acceleration constant of gravity. we can increase viscosity of suspension, so particles settle down slowly. To increase viscosity, we can add polymers or sugars. But with centrifugal method, this method has detector to measure mass & get weighted average. Other caveats: particles must be completely insoluble in media you"re using, particle concentration must be kept low to allow reaching terminal velocity, very large particle will disrupt flow through fluid. Laser for larger particles; dynamic laser for very smaller particles. Dry/wet samples (aerosols, powder, suspensions, emulsions) broader applications.
