  We report filling-fraction dependent dielectric spectroscopy measurements on
the relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silica
nanochannels. In the film-condensed regime, a slow interface relaxation
dominates the dielectric spectra, whereas from the capillary-condensed state up
to complete filling an additional, fast relaxation in the core of the channels
is found. The temperature-dependence of the static capacitance, representative
of the averaged, collective molecular orientational ordering, indicates a
continuous, paranematic-to-nematic (P-N) transition, in contrast to the
discontinuous bulk behaviour. It is well described by a Landau-de-Gennes free
energy model for a phase transition in cylindrical confinement. The large
tensile pressure of 10 MPa in the capillary-condensed state, resulting from the
Young-Laplace pressure at highly curved liquid menisci, quantitatively accounts
for a downward-shift of the P-N transition and an increased molecular mobility
in comparison to the unstretched liquid state of the complete filling. The
strengths of the slow and fast relaxations provide local information on the
orientational order: The thermotropic behaviour in the core region is
bulk-like, i.e. it is characterized by an abrupt onset of the nematic order at
the P-N transition. By contrast, the interface ordering exhibits a continuous
evolution at the P-N transition. Thus, the phase behaviour of the entirely
filled liquid crystal-silica nanocomposite can be quantitatively described by a
linear superposition of these distinct nematic order contributions.
