Albert Magnin

Hi! thanks for your coments and answers.

The samples are Newtonian fluids, and we use to measure in Brookfield a spindle and the rheometer we use it with plane-plane system.

My problem is that in the industry where this resines and adhesives are producided (and where are they sent as raw material out of the industry) they occupy viscosimeter of Brookfield, and is very difficult that they change to rheometer.

This is why that i need related both measurements.

Thanks again!

I think for a comparison between the mesured viscosity from these devices you should choice a Newtonian sample having a constant viscosity since the viscosimeter that you use it is dedicated only the newtonian solutions. If it is not the case you can not make a such comparison.

The usual Brookfield spindles do not give a well-defined shear rate. Unlike the cone-plate geometry, the shear rate is not constant throughout the sample. For a newtonian liquid this does not matter much. If the sample is non-newtonian, the effective viscosity will be different in different places. The details of this effect will depend on the rheology of the liquid, so it is not possible (or at least very difficult) to convert accurately from Brookfield to cone plate.

You can, however, calculate an approximate conversion that will apply to the sort of samples you investigate. Take a standard or model sample and measure the viscosity vs. shear rate with cone-plate. Then measure it with the Brookfield spindles and rotation rates that interest you. A comparison gives the effective shear rate for the Brookfield measurement.

I did this once using a model shampoo (laureth sulphate + NaCl); it was shear-thinning and fairly similar to the samples we were interested in. This method only works for non-newtonian liquids, as there has to be a significant change of viscosity with shear rate.

I was wrong, and they are NOT Newtonian liquids, in fact I have curves, they are thixotropic pseudoplastic liquids.

With all of this COVID-19 contingency, I can't go to the lab for testing (but I expect standard measurements on both equipments), so I'd be very interested to know what correlation I use and how you did it experimentally. Dennis John Miller

Unfortunately I don't have the exact details, as the work was done in my previous firm and I am now semi-retired. But I have a recipe for a model shampoo used in a related test:

9.2 % Laureth sulphate, 2.8 % cocamidopropyl betaine, 2.3 % NaCl. It is shear-thinning, but without a yield point. The limiting viscosity of about 44000 mPa.s. The viscosity stars to decrease above about 5rpm with the Brookfield measurements. In principle, one could use a commercial shampoo instead of making up the model mixture. However, I would recommend using a reference that is similar to the samples you need to measure.

The experiment is quite easy: make a set of measurements with Brookfield at various rotation speeds and a set with the rheometer at various shear rates (or rotation speeds). Then you just read from the plots to get the shear rate equivalent to any Brookfield rotation rate.

Hope this works with your setup when you manage to get back to the lab.

I have used both Brookfiled viscosimeter and conventional rotating rheometer. Unfortunately, Brookfield viscosimeter provides a relative viscosity which is qualitative and depends on several parameters such as : the spindle size and the used viscosimeter. Indeed, using 2 spindles may give 2 different viscosities. Brookfield viscosimeter are used as qualitative devise in industry.

In the other hand, The MCR72 Anton Paar rheometer (or another commercial one) allows measuring the intrinsic viscosity which is real and independent of the device. It is intrinsic to the sample.

There are devices with which the absolute values of rheological parameters can be measured, but others do not. The latter is the Brookfield viscometer. It is impossible to compare the absolute value of a given rheological parameter with its relative value. There are many such devices related to a specific industry.