Viscosity: Other Factors

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Viscosity Other Factors

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Pressure

• The viscosity of most foods does not vary at
  pressures between 0-100 atm

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Solute Molecular Weight

• Typically, viscosity increases with MW
• Non-linear relationship
• The intrinsic viscosity often follows the
  Mark-Houwink relationship
• h KMa

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The slope contains information about the shape of
the molecule a 0.5 ? flexible polymer chain
in ideal solvent 0.5 lt a lt0.8
?flexible polymer chain in good
solvent a gt 0.8 ? stiff chain
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Macromolecule Solvent K x 102 a
Polystyrene Benzene 0.95 0.74
Amylose 0.33N KCl 11.3 0.50
Various proteins 6M guanidine HCl 0.1M b-MeSH 0.716 0.66
PVOH Methanol 0.02 0.76
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Source Viskotek
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• For many polymers, viscosity varies with chain
  length Zw
• A critical chain length (Zc) exists, such as
• Below Zc
• Above Zc

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General Theory

• Albert Einstein (1906) describes viscosity of
  solutions containing rigid spheres
• When particles are introduced to a fluid, more
  force is required to maintain same shear rate.
  Particles dont deform, so fluid must be forced
  around them

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The viscous drag depends on the volume fraction
of particles
Medium f
Low volume fraction f
High volume fraction f
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where n is a shape factor ( 5/2 for spheres)
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For concentrated solutions
Expressed in terms of concentration
h KMa
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Concentration

• Generally, viscosity increases with concentration
  of solute. A power law may apply over limited
  concentrations

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http//www.fao.org/docrep/field
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Akucell cellulose gum
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Ions may interact with polymers
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Suspended Particles

• Particles usually increase viscosity slightly at
  low concentrations
• More effect at higher concentrations, and leads
  to pseudoplastic behavior
• Fruit and vegetable juices, purees

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http//ciks.cbt.nist.gov/garbocz
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