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### Topic: Rheology - Arrhenius Equation  (Read 1612 times)

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#### apetroro

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##### Rheology - Arrhenius Equation
« on: July 05, 2023, 03:22:46 PM »
Hi guys, how are you???

I need some help, I'm new to this forum.

I did some rheology experiments (oscillatory tests) to determine G', G'' and complex viscosity during the formation of a polyurethane-elastomer.

I have G' G'' data and complex viscosity for 60C, other data for 70C and other data for 80C.

How do I determine the Arrhenius parameters??? I'm not understanding how to plot the graph with this data to have ln(viscosity) versus 1/T.

Big hug!

#### Enthalpy

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##### Re: Rheology - Arrhenius Equation
« Reply #1 on: July 21, 2023, 05:49:29 PM »
Welcome, apetroro!

An Arrhenius plot uses the absolute temperature (in Kelvin usually), or rather its reciprocal 1/T.
The other axis needs to take some reference value that divides the measures before you take a log, usually in base 10.

However:

I don't expect straight lines for G' nor G" on an Arrhenius plot. Only at extreme values of G". G" tends to show a maximum, not a line, around the glass transition temperature. It's even a standard way to sniff where Tg is. It's also a way to check if the polycondensation is finished.

But once you figured out what the curves do, over some limited domains the plot is linear and you can model the values with different Arrhenius expressions. After noticing the domains on the curves, you best determine the Arrhenius constants from the data, not the curves.