I am using weak gels models for food as suggested by Dr. D.Gabriele, and estimated rheological units such as AF (strength of interaction) and z (co-ordination number). Now i would like to plot graphs relaxation spectrum H(λ) and apparent elastic modulus Ge*(ω). For understanding the strength of network (both temporary and permanent). How to obtain these values from any raw frequency sweep data?
I am working in similar things for creep data using TA HR3 rheometer and I am using thier software. You can use in-built software for the instrument. Or mathematically you can do using ant stat package.
Dear Kiran,
The most easiest way is indeed by the rheometer software. If you are dealing with gels be aware of their nonlinearity! To capture these effects, you must ensure that your raw data are really raw and not filtered or processed by the rheometer software. If you have the raw data, there are two main data processing procedures. You may find more informations in PHYSICAL REVIEW E 84, 051502 (2011), http://pre.aps.org/pdf/PRE/v84/i5/e051502.
Dear Javier sir and Andreas sir
First I would like to thanks for your concern.
Prof. Javier sir, Presently I am using Malvern, Bohlin Rheometer. In this there is no direct option available for Relaxation spectrum measurement by using oscillation or any other experiment. So, can u provide more details on ant stat package and its usage for obtaining rheological units.
Andreas sir, please guide me how to obtain real raw data, because as such we do not have any provision to note down data externally. Mostly, I can get instrument numbers such as trust and angular velocity. And by putting formulas in it I can get other data.
The first step is to get G'G"(w) data over a wide frequency range (as wide as possible. There are constraints, obviously). Then calculate the discrete spectrum from that data set. A powerful method is described in
Baumgaertel M, Winter HH (1989) Determination of the discrete relaxation and retardation time spectra from dynamic mechanical data. Rheol Acta 28:511519
Baumgaertel M, Winter HH (1992) Interrelation between continuous and discrete relaxation time spectra. J Non-Newtonian Fluid Mech 44:15-36
The breakthrough came from what I call the Baumgaertel Plot: Figure 17a in the 1992 paper. Baumgaertel realized that there is an intermediate number of discrete modes which gives the best fit and is still meaningful. A higher number of modes would fit the noise in the data but would not represent the the material sample.
Thank You Winter sir, I will certainly go through research articles as suggested by u.
Dear Kiran,
Unfortunately I have never worked with a Bohlin rheometer. You can try to plot Lissajous figures to characterize the nonlinearity of your samples. I think will be a good idea to follow the advice of Henning Winter since he is the expert in the field of relaxation spectra.
The data amnalysis package from ta instruments does it with a single click
Dear Andreas sir,
Thank you for your concern. At present I am slowly working on those concepts. However, Winter sir papers really creating interest for correlating the structural aspects with mechanics.
Dear Calderas sir
I would like to share my personal experience during lab work, I approximately handled more than 2500-3000 sample for rheology. However, many times scholars comes with very innovative ideas for measuring rheology, which I found very interested and it was difficult, as the options were very limited in our rheometer. So, when I go through many references it was TA instrumentation work. Sir, I love to handle TA instrument for rheology.
As far as I know the data analysis software is free to download.
http://www.tainstruments.com/main.aspx?id=292&n=2&siteid=11
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