Currently I am gathering data to make viscosity-temperature curves on a Brookfield LVT. I keep running into a problem of inconsistent viscosity readings from my LVT. I generally work from 70-100 degF and take data points within this range. The problem is that as I increase the temperature there is not always a distinct trend in the data i.e. viscosity is increases with temperature. Sometimes I will increase the temperature by 5 degF and I will get a value higher in viscosity. This shouldn't be the case as liquids have an inverse viscosity-temperature relationship. Attached are some example graphs of the data I collected. The LVT gets calibrated weekly with Brookfield calibration fluid. The products are highly non-Newtonian (shear thinning, thixotropic). Could this be a problem with shear history of the fluid or the complex non-Newtonian nature? I have thought of solvent evaporation as an explanation but I am not convinced this is the case, yet. As I have faith in the reliability of the viscometers/thermometer calibration.
I multiple Brookfield RVTs and LVTs available as well as a R/S-CPS+ rheometer.
Dear Chad Anthony Keyser, the key parameter in Brookfield viscosity measurements is the judacious choice of the appropriate spindle. On the other hand I don't think this technique is suitable to study thèse shear phenomena. Other thing to consider when raising temperature is to give time to reach equilibrium. My Regards
Dear Chad,
how do you set your sample temperature? The device you use cannot actively control temperature, even if you sample is pre-heated it will change (decrease) during the measurement.
Abdelkader already mentioned the necessity to equilibrate temperature of the sample (and the spindle!) for at least something like 10 minutes before the measurement.
Even assuming correct temperature of your sample, data scatter shows that it is hardly possible to resolve a temperature effect here. I do not know your sample, but many samples would show a viscosity decrease that is far beyond the at best ~10% decrease you observe for this temperature change (70-100 F).
As a side note, an apparent increase of viscosity with temperature is sometimes observed for very low viscosity liquids (like water) due to turbulent effects (vortices) that are more likely for higher rotational speed (here: constant) and lower viscosity values (resulting from higher temperatures).
Best wishes
Christopher
I do not seem to find the fluid that you are testing. Different fluids have diverse time and temperature-dependent behavior. It could also be that the fluid you are testing requires a more advanced rheometer than a Brookfield viscometer and you may even go to the extent of needing oscillatory dynamic rheology. The sample preparation and shear history also must be reproduced with accuracy to reproduce results.
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