I have a question about the viscosity of beta-glucan solutions. I have made 1% of beta-glucan solution and pour it in the rheometer cylinder. The results I have achieved are different than those from literature. Does anybody could tell me why the viscosity in my samples increase from 0.01 to 1000/s (red color on chart) and basing on the same MM section the results achieved by authors were different (other charts)?
It is possible that you have secondary flow. That is, you are outside the laminar flow regime. Look at the geometry used for the published measurements. Check your Reynolds number is below 100 for laminar flow. If you have cone and plate or parallel plate geometry you could compare.
Hi Marcin,
Could there have been an issue with sample loading? Unexpected flow curves may be generated if there are bubbles within the sample, or evaporation or edge fracture occur during the course of the measurement.
The geometry used is cylinder. The problem is that the sample has totally different diraction than those from literature. I am going to check Reynolds numer. However, could it be caused with preparation of the solution as well?
Viscosity is too low (1-5 mPa s) to measure in that device. You must use a double gap geometry or a cone (1 degree) and plate system with a big radius (7.5 cm). Try water first in a 100-300 1/s shear rate range to verify that the rheometer is ok.
The change in viscosity is smaller (i.e nano Pa.S),sample may not be homogenized before test or you can check same behavior using cone and plate rheometer or capillary viscometer . If you still get same curve then your sample shows Dilatant nature of rheology. Dilatancy may occur due to some formation built up during increasing shear rate. You may justify this formations by composition of your fluid.
first of all you have to check that you are using exactly the same conditions as the references you have consulted, such as:geometry and dimensions, temperature, beta glucan concentrations and working shear range. Then you have to see whether you you really have "shear-thickenning", as a result of "structure formation" during your tests, this might be caused by enhancing components interactions by shearing during the measurement, meaning that your sample might be different to that of other colleagues
Almost certainly the cause of what you see are inertial effects, i.e. your apparent "viscosity" is not the true sample viscosity, as indicated by previous replies. For water-like viscosities like this you could even consider capillary viscometry if you have access to such devices, as long as you do not have significant shear thinning (low conc.) you should have very accurate results.
Since you are using concentric cylinder attachment for measurement of shear stress/viscosity. However sample concentration is low their may be a chance of Taylor vertex problem associated with concentric cylinder attachment. This problem arises at low concentration or high temperature studies at higher shear rates. This factor increase the viscosity of samples
Beside of already shared information above I do remember an article by Chrstian Clasen, who also worked with Glucane: Rheo-optical studies of barley (1->3)(1->4)-β-glucan solution: detection of the flow behavior of aggregates in the sol state Christian Clasen, Werner-Michael Kulicke Journal of Rheology 47, 321-335 (2003)