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Time Dependent Properties

Time Dependent Properties. Viscosity and Creep. Viscosity. Polymers do something when you dissolve them in a solvent: They make the solution viscous. Viscosity

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Time Dependent Properties

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  1. Time Dependent Properties Viscosity and Creep

  2. 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.

  3. Viscosity Demonstration And Select ‘Viscosity Measurements’ for Demonstration

  4. 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

  5. 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.

  6. 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.

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

  8. 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

  9. 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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