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Viscoelastic properties of hydrogels (DMA)

  1. May 25, 2014 #1

    I am a Bachelor Student of biomedical engineering and I have a question regarding the complex compressive modulus. I am really a newbie in this field, hopefully somebody can help me.
    I have measured four different hydrogel films to compare with the same conditions using a dynamic mechanical analyzer (DMA, measured in compression mode with a sinusoidal deformation of constant amplitude, ε=0.1%).
    Now the results show that the materials that have the highest storage modulus also have the highest tan δ, which is a bit confusing to me as I though when measuring viscoelastic materials with a DMA it should always the other way round (so the ones with the highest E' should have the lowest tan δ). I am attaching E', E'' and tan delta graphs so you see what I mean.
    Thank you!

    https://dl.dropboxusercontent.com/u/38703467/storageModulus.gif [Broken]
    https://dl.dropboxusercontent.com/u/38703467/lossModulus.gif [Broken]
    https://dl.dropboxusercontent.com/u/38703467/tanDelta.gif [Broken]
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. May 28, 2014 #2
    The storage modulus is an absolute quantity, and tan δ, the ratio of the loss modulus to the storage modulus is a relative quantity. So it isn't really relevant to compare the storage modulus of a given material to its tan δ . The tan δ in the figures appears to be roughly decreasing with frequency, which is what would be expected.

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