Dual Arrhenius model is well known to be good for predicting viscosity at different time /temperature for thermoset adhesives. However I realized that it does not work properly and it vastly deviates from experimental viscosity values when low temperature ranges (below 50C) are used. Is there any solution for this? any suggestions?
There are other empirical equations. The "Arrhenius" eqn, really the Andrade eq as Arrhenius did not study viscosity, fits very few materials. It is just a matter of finding which fits best with the smallest number of coefficients.
2 parameter: eta=exp(a+b/T^n). n=3 is the Litovitz eq but other values up to 4 have been used. [Litovitz, T. A. Temperature dependence of the viscosity of
associated liquids. J. Chem. Phys. 1952, 20, 1088-1089, 1980]
3- parameter: VFT or Vogel-Fulcher-Tammann eta=exp(A+B/(T-T0)) works well with high-viscosity materials but you need a 80-100K temperature range and a non-linear least squares program to obtain reliable estimates of the parameters .
I totally agree with Pr. Kenneth R. Harris
Generally, The Arrhenius model is reliable in a certain range of temperature. When you go far away, the model fails, ...
You must use non linear model [ln(viscosity) = f(1/T)]. The most used is VFT, because it can give you the interesting T0 parameter which it can have a physical significance for your studied system.
I have offered some specific empirical models adapted to their studied systems in different domains out of my specialty, maybe I can suggest you an expression if I see the plot of your experimental data, maybe it's a complex system!
Thank you all
Dear Noureddine it is an exponential graph (viscosity vs time) and by increasing the temperature the adhesive cures faster so the graph becomes exponential at lower time when you increase the isothermal temp.
Mohammad Tasooji,
any news for this topic? just working on my bachelor and have a similar struggle...
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