Time Dependent Properties

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Time Dependent Properties

• Viscosity and Creep

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Viscosity

• Polymers do something when you dissolve them in a
  solvent They make the solution viscous.
• Viscosity
• The internal resistance to flow existing between
  two liquid layers when they are moved relative to
  each other. This internal resistance is a result
  of interaction between liquid molecules in
  motion.

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Viscosity Demonstration
And Select Viscosity Measurements for
Demonstration
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Viscosity

• You see this all the time
• Polymers are used as thickeners in things like
  shampoo and even ice cream.
• This thickening effect can be used to estimate a
  polymer's molecular weight.
• Temperature can have an effect

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Why do polymers make solutions viscous?

• Polymers move very slowly, or at least, they move
  a lot more slowly than do small molecules.
• The faster molecules in a liquid move, the more
  easily the liquid will flow.

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Do polymers make the solvent molecules move
slowly, too?

• Yes.
• Ex. Getting stuck behind a huge slow truck on a
  one lane highway.
• And intermolecular forces
• If there are any attractive secondary
  interactions between the polymer and solvent
  molecules, the small solvent molecules can become
  bound to the polymer and they move with the
  polymer.

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Viscosity

• Bigger polymer molecules make a solution more
  viscous than small ones do.

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Creep

• Creep the gradual deformation of a material
  under a load that is less than the yield strength
  of the material
• Significant deformations with small loads but
  over long periods of time

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Creep

• The amount of creep is strongly dependent upon
  the amount of the load, the time the load is
  applied and the temperature of the material.
• Increases in any of these parameters will cause
  the creep deformation to be greater

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