I have tried to replicate VFT curve fitting results extracted from literature without success. Attached is the excel file. Thank you in advance
The Vogel-Fulcher-Tammann (VFT) correlation is usually given in the form log (|η|) = A + B / (T - To). You may simply solve the corresponding system of (3) equations for just 3 data points (viscosity vs. temperature) to find estimates for the parameters (A, B, To). To find this system solution is straightforward enough, but it can be also found at Horst Scholze's textbook (*). If more data points are available, you may consider to refine this solution by means of iterative (non-linear) least-squares fitting. A plot of log (|η|) vs. B / (T - To) (Fulcher plot) is quite convenient to linearly display the viscosity experimental data while accessing scattering around the trendline.
(*) "Le Verre ― Nature, structure et propriétés", Institut du Verre, Paris, 1980, p. 133.
Oops. For some reason, the temperatures that you have used in your fit are not the same as those in your table of results.
Just copy and paste the temperatures from your results table to the temperature column in your fit. Run Solver again and you will get the correct result...
My bill is in the post :-).
Thank you all for your advices!
@amin, the rheometer software did not contain the facility for this analysis. Appreciate if you could suggest me another software.
@Carlos, i have used the VFT equation as given in the data sheet. Basically, i could not replicate literature data using the VFT fitting.
@Alan, interesting observation and thanks. I tried per your advise but i got zero values for one of the coefficients (A=0) while the literature data suggests otherwise (~-3).
Kindly refer to the attached file.
Strange. I'm sorry that I did not keep my version of your file. The temperatures in your fit table were not the same as in the data table at the top of the spreadsheet. When I corrected them and ran solver with the right temperatures, I got almost exactly the data fit in the literature, by minimizing the sum of the absolute deviations.
I hope this link will help you. Very useful article.
https://pubs.acs.org/doi/abs/10.1021/ma071788%2B?journalCode=mamobx
good luck
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