THERMODYNAMIC INSIGHTS INTO THE AGGREGATION OF CARBOXYLATE IMIDAZOLIUM IONIC LIQUIDS WITH HYDROXYPROPYL CELLULOSE

Mixtures based on cellulose derivatives/ionic liquids (ILs) have been used in the food, pharmaceutical, cosmetic, and petroleum industries. One of the main applications of these mixtures in the oil industry includes their use as viscosity modifiers in enhanced oil recovery (EOR)¹. This work investigates the aggregation thermodynamics of 1-alkyl-3-methylimidazolium carboxylate ILs (CnMIMCmCOO-, n = 12, 16 and m = 3, 6) with hydroxypropyl cellulose (HPC) and the modification of its rheological properties in the dilute and semi-dilute regimes, respectively. The effects of the alkyl chain length of ILs, type of anions (butanoate or heptanoate), and concentration of ILs on the binding to HPC were evaluated by conductivity, surface tension, and viscosity. The results indicate that the auto organization occurs by hydrophobic interactions between the alkyl chain of ILs and HPC, which are proportional to the length of the alkyl chain length of ILs and the hydrophobicity of the anions. The rheological results showed that the addition of carboxylate ILs produced a significant increase in the viscosity of HPC solutions, which varied depending on the concentration, alkyl chain length, and type of anion of the ILs. Moreover, the presence of ILs produces a salt-in effect, delaying the HPC phase separation. These findings are consistent with the group's previous studies involving homologous ILs (CnMIMBr)^2,3, highlighting the role of ILs in the modification of rheological properties of HPC, and creating new possibilities for the design of complex mixtures that can be used in several industrial applications.

Acknowledgment: The authors are grateful for the financial support from CAPES, FAPERGS, and CNPQ.

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