Viscoelastic properties of hydrogels (DMA)

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In summary: Bachelor Student of biomedical engineering and is looking for help understanding the complex compressive modulus. He performed measurements on hydrogel films using a dynamic mechanical analyzer and is confused by the results. The materials with the highest storage modulus also have the highest tan δ, which goes against his expectation. However, it is important to note that the storage modulus is an absolute quantity while tan δ is a relative quantity. Additionally, the figures show that the tan δ decreases with frequency, which is expected behavior.
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neejam
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Hi,

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]
 
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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.

Chet
 

1. What is the significance of studying the viscoelastic properties of hydrogels?

The viscoelastic properties of hydrogels play a crucial role in their mechanical behavior and performance. Understanding these properties is essential for various applications such as tissue engineering, drug delivery, and biomedical devices.

2. How are the viscoelastic properties of hydrogels characterized?

The viscoelastic properties of hydrogels are typically characterized using dynamic mechanical analysis (DMA), which measures the changes in their mechanical properties as a function of frequency and temperature.

3. What factors affect the viscoelastic properties of hydrogels?

The viscoelastic properties of hydrogels are influenced by several factors, including the type and concentration of crosslinking agents, the degree of swelling, and the molecular weight of the polymer chains.

4. How does the water content of hydrogels affect their viscoelastic properties?

The water content of hydrogels has a significant impact on their viscoelastic properties. Higher water content leads to increased swelling and a decrease in the stiffness and strength of hydrogels, resulting in a more viscoelastic behavior.

5. What are the applications of studying the viscoelastic properties of hydrogels?

Studying the viscoelastic properties of hydrogels has various applications, including designing and optimizing hydrogels for specific biomedical applications, predicting their behavior under different environmental conditions, and developing new materials with tailored properties.

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