I am currently working on cosmetic formulations.
I transferred the samples of emulsion into 50 ml bottles.
They were then held for a week at either room temperature (23 ±1 °C) or -15 ±1 °C before being heated to 23±1 °C.
However, when I measured the viscosity of samples, it appears that the cold sample is more viscous after thawing.
Does anyone have any ideas on the cause of the increase?
Zhi Zhao
When you cool your emulsion, it turns into a jelly. If the jelly was stored for a long time, irreversible changes occurred in it under the influence of bacteria and time. After heating, these changes remain and change the viscosity. Compare the IR spectrum of the jelly immediately and after storage and you will see the difference in the spectrum.
Zhi Zhao
Natural fats are composed of esters of glycerol and fatty acids. They are hydrolyzed, glycerol is polymerized, unsaturated acids have double bonds, through which they are oxidized and polymerized.Hydrocarbons also have molecules with double bonds.
Your viscosity changes are not unusual and may be explained very easily by looking at the fundamentals of thermodynamics, such as GIBBS FREE ENERGY: dG = dH + T dS
During your processing (working conditions), you are changing i.e. the temperature and the entropy (distribution coefficients and the size as well as the number of oil droplets in a thermodynamic instabile O/W-emulsion, etc.). This will have drastic changes in viscosity (without any changes in chemical composition!)
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