Designing Novel High-Performance Shale Inhibitors by Optimizing the Spacer Length of Imidazolium-Based Bola-Form Ionic Liquids

The alkyl chain lengths of ionic liquid shale inhibitors are critical to their inhibitive properties. To design high-performance shale inhibitors with bola-form molecular structures, a series of imidazolium-based bola-form ionic liquids (IBFILs) with different spacer lengths (s), denoted as MsM (s = 2, 4, 6, 8, 10), were synthesized, and their inhibitive properties were evaluated through linear swelling tests and hot-rolling recovery tests. The results indicated that the optimized IBFILs with a proper spacer length that had six carbon atoms performed best in linear swelling rate tests and hot-rolling recovery tests. Based on the investigation of interaction modes between MsM and clay materials via contact angle measurement, ζ-potential measurement, X-ray diffraction, and molecular electrostatic potentials calculation, the possible explanation for the effects of spacer lengths on the inhibitive performance of MsM was proposed. The IBFILs with medium spacer lengths decreased the montmorillonite (Mt) ζ-potential close to zero, and the intercalated MsM in the clay interlayer acted as a binding bridge to reduce the Mt interlayer distance. This work demonstrates that the optimization of spacer lengths is crucial to the inhibitive property of IBFILs, which could be inspiring to the designing of other novel shale inhibitors.