I measured the viscosity versus shear rate curves of surfactant solutions (non-ionic) and found pseudoplastic nature, which is normal. However, interestingly I found the viscosity to increase very slightly (instead of decreasing) with increase in temperature. Normally liquids show viscosity decrease with temperature due to reduced forces of cohesion among surfactant molecules. But the reverse trend for the non-ionic surfactant solution is noteworthy. Can anyone help me in this regard ?
Are there any earlier papers or manuscripts that report this interesting behavior in which viscosity of surfactant solution increases or remains nearly constant with temperature?
The relationship between viscosity and temperature is inverse in general. It is mathematically defined by a well known equation called the arrhenius equation. So increasing temperature reduced viscosity. However an exception would be if the surfactant has the ability to self-assemble with increasing temperature forming liquid crystalline systems. Then you may experience an increase in viscosity. Look at thermotropic liquid crystalline systems to develop better understanding.
For non-ionic surfactants, increase in temperature may result in clear solution turning to cloudy due to phase separation. This critical temperature is the cloud point (Cp).
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