Improving thickening and emulsification performances of cellulose nanocrystals by alkylation modification for enhanced oil recovery

Improving the thickening and emulsification performances of cellulose nanocrystals (CNCs) is crucial for their effective application in enhanced oil recovery (EOR). In this study, three kinds of amphiphilic Cn-CNCs (n = 8, 12 and 16, n represents the number of carbon atoms in the alkyl chain) were successfully prepared by alkylationmodified CNCs. Compared to CNCs, Cn-CNCs exhibited a stronger performance of thickening the viscosity of aqueous phase, especially C12-CNCs. When the concentration was 1 wt% and at a fixed shear rate (10 rad/s), the viscosity of CNC dispersions was 13.1 mPa center dot s, while the viscosity of C12-CNC dispersions was 33.7 mPa center dot s. The enhanced thickening was attributed to hydrophobic association in addition to hydrogen bonding. In addition, C12-CNCs also exhibited superior emulsification performance due to the lower interfacial tension (IFT) and the thicker oil-water interfacial film. Furthermore, the oil displacement performance of C12-CNC dispersions was better than that of CNC dispersions, which was attributed to the improvement of sweep efficiency and oilwashing efficiency. This study provided the guidance for the effective application of CNCs in EOR.