Many different methods
have been developed to investigate fluid–solid
interactions in nanoporous systems. These methods either only work
in the liquid phase or provide an indirect measurement by probing
the fluid–solid interaction based on a measured property change
of the fluid or solid under different sample conditions. Here, we
report a direct measurement technique using NMR dipolar cross-relaxation
between the nanoconfined fluids and the matrix solids. The method
was tested using a methyl-functionalized mesostructured silica saturated
with methanol as a model sample. A formal theory was established to
describe the enhanced dipolar cross-relaxation interaction between
the nanoconfined fluids and the matrix solids. Both the experiment
and theory showed that nanoconfinement of the fluids enhances the
dipolar cross-relaxation interaction between the fluid and the matrix
solids, which can be applied to investigate the fluid–solid
interaction for various materials of a similar nanostructure.