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.