The instrument pictured above is a Dynamic Mechanical Analysis apparatus (DMA).  From the term dynamic, we see that the technique is ever-changing in analysis or there is an oscillatory strain or stress applied to the sample to probe molecular motion while temperature is increased during the experiment.  The experiment can also hold temperature constant while altering the oscillatory frequency.  Regardless, the mechanical strain energy generated can be stored elastically or dissipated as thermal energy (by molecular motion) during the mechanical strain cycle.

       A few things to think about in DMA are as follows:

1.  The ability of a material to store or dissipate mechanical energy is a function of temperature and time.
2.  During a mechanical relaxation, the frequency of molecular motion matches the frequency of the oscillatory mechanical strain
     cycle.
3.  DMA probes the bulk properties of materials.
4.  For polymers, many relaxations can occur because of the size, shape, spatial arrangements, and interactions of the polymer
     chains.

      These relaxations of viscoelastic (elastic yet viscous materials) are represented in the following expanded DMA spectrum.  Treat E, Young's modulus, as the stiffness of the sample for simplicity's sake.

      How does this fit into the IPN scheme of things?  Well, since IPN's are the best materials for producing a broad Tg which will subsequently increase the materials ability to absorb energy, DMA will be a primary technique to analyze this absorption.  IPN's are frequently used as damping or energy absorbing materials.  DMA provides an energy at certain frequencies and is thus a good technique for the characterization of the materials.  Depicted below is a DMA spectrum which will provide us with a good feel for the information which can be generated with the technique.  Take note of the change in Tg for the materials as we go from a polyurethane homopolymer to a PU/PVE IPN.

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