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Fundamental Physics and Chemistry Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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3. Gravitational Destabilization of Stationary States
Pages 71-76

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From page 71...
... Einstein showed that for dilute suspensions of spheres the shear viscosity depends linearly on the volume fraction. Data on such systems deviate from linear behavior, with much scatter at high concentrations; there is still no convincing theoretical description of such behavior.
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From page 72...
... Obviously, working with smaller gravitational levels allows ~ to be increased without encountering significant sedimentation problems, thus enabling us to work closer to the critical concentration. SHEARED SUSPENSIONS OF GRANULAR MATERIALS Suspension mechanics ~ the description of the theological behavior of all sorts of suspensions, but the focus over the past 200 years has been on rigid particles suspended in liquids or gases.
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From page 73...
... Since the particles themselves vary in their density and elastic properties, have rough surfaces, and need not be spherical, there are many interesting aspects to any experimental or theoretical study. It is crucial that the various mechanisms be separated in an experimentally meaningful way, but in the terrestrial environment particle behavior is dominated by gravitational effects, making such separations impossible.
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From page 74...
... Even the simplest diffusion mechanism presents a major theoretical challenge, especially when the condensing phase occupies a nonnegligible fraction of the volume of the system and the droplets are close enough to each other SO that deformation of their shapes may be important. At present, the state of our understanding of these processes is so rudimentary that a metallurgist, using the most modern tools of analytic microscopy, cannot tell
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From page 75...
... Even when attempts have been made to use working fluids for which the two separating phases have nearly the same density, it has not been possible to prevent precipitation patterns from breaking down under gravity for long enough times to span the theoretically interesting range of behavior. It ~ quite possible that this observational problem could be solved ~ a microgravity environment; thus, the results would be of fundamental significance.
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From page 76...
... Once stable aggregates of macroscopic size have been oh tained, a host of exciting experiments on a single fractal become possible: elastic, electrical, and thermal transport properties can be measured. At present, these measurements are impossible because the medium dominates bulb measurements on aggregate ensembles.
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Key Terms

  • gravitational effects
  • thermal energy
  • stable aggregates
  • condensing phase
  • aggregation process

  • precipitation pattern
  • fractal growth
  • mechanism involves
  • surface tension
  • growth law

  • pseudo thermal
  • neutrally buoyant
  • theological behavior
  • suspension mechanics
  • shear viscosity

  • fractal gel
  • involve direct
  • material flows
  • viscosity depends
  • viscosity diverges

  • theoretical challenge
  • separating phases
  • particles suspended
  • volume fractions
  • aggregates join

  • binary mixtures
  • mechanisms resemble
  • phase tend
  • work closer
  • medium dominates


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