The phase behavior of a mixture of
isobutyric acid and water confined
in mesoporous SBA-15 silica material is studied by a combination of
solid-state NMR spectroscopy and molecular dynamics (MD) simulations.
The combination of these two techniques shows that the iBA-rich phase
is close to the pore wall and the water-rich phase is in the center
of the pores. The MD simulations reveal that this surprising phase
behavior is mainly the result of the minimization of the hydrogen-bonding
enthalpy. Moreover, the simulations show also that upon increasing
temperature the relative water concentration increases at the pore
surface, which is attributed to entropic contributions which lead
to a more thorough miscibility. These results solve a long-standing
problem of the microphase separation inside these materials.
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