Hello,
I made 2% xanthan gum solution and measured its viscosity while increasing temperature of the solution.
I guess viscosity of the solution should be decreased while heating, due to degradation of the polymer, according to the previous researches.
But I found that viscosity of my xanthan solution had increased continuously while heating and then suddenly dropped down quickly at 95'c.
Do you think it's normal to have the viscosity increasing while heating??? I want to know why it increases....
Please help! :"(
(+) I made the solution with 80'c water while stirring vigorously and homogenized for 15min at 5000rpm. So I assume all the dry xanthan powders were solublized enough.....
Dear all, the normal behavior is that viscosity decreases upon heating. One possible explanation is that the xanthan was not fully solubilized either to an extremely high molecular weight or the time to achieve good solubility is not respected before testing. If this is the case, upon heating, xanthan solubility is enhanced where chains reach more extended conformations which induce increase in viscosity. My Regards
I suppose that you measured the viscosity of your sample, "AQUEOUS" solution of gum, in a temperature range starting from RT up to 100 C (or higher?). Could you please define your measuring device and conditions? Did you concern the effects of water evaporation issue and use a sealing material like silicon oil? Reason would simply be related to evaporation...
Dear all, the normal behavior is that viscosity decreases upon heating. One possible explanation is that the xanthan was not fully solubilized either to an extremely high molecular weight or the time to achieve good solubility is not respected before testing. If this is the case, upon heating, xanthan solubility is enhanced where chains reach more extended conformations which induce increase in viscosity. My Regards
Dear Lil;
The increase in temperature leads to an increase in viscosity due to the formation of packets or crystallized domains. For further details, please see this thesis en French. https://inis.iaea.org/collection/NCLCollectionStore/_Public/37/038/37038443.pdf?r=1&r=1.
With my best regards
It has been reported that xanthan in water undergoes a conformation transition when heated. At high T (and low ionic strength) it adopts the conformation of a disordered coil, at low T it adopts an ordered conformation (single or double helical, this is a matter of debate). Transition temperature Tm has been reported at 55 degree C (R.O. Mannion et al., Carbohydr. Polym. 19 (1992) 91-97). For the conformational transition, see E.R. Morris et al., J. Mol. Biol. 110 (1977), 1, and I.T. Norton, J. Mol. Biol. 175 (1984) 371. This may well be the cause for the phenomenon observed by you.
There is a rather vast literature on xanthan conformation, especially in what regimes random coil, single and/or double helical conformations prevail. As I am retired I have no access to this literature to advise you in more detail.
Because of these transitions, the preparation of xanthan solutions needs rigorous standardisation.
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