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We report filling-fraction dependent dielectric spectroscopy measurements onthe relaxation dynamics of the rod-like nematogen 7CB condensed in 13 nm silicananochannels. In the film-condensed regime, a slow interface relaxationdominates the dielectric spectra, whereas from the capillary-condensed state upto complete filling an additional, fast relaxation in the core of the channelsis found. The temperature-dependence of the static capacitance, representativeof the averaged, collective molecular orientational ordering, indicates acontinuous, paranematic-to-nematic (P-N) transition, in contrast to thediscontinuous bulk behaviour. It is well described by a Landau-de-Gennes freeenergy model for a phase transition in cylindrical confinement. The largetensile pressure of 10 MPa in the capillary-condensed state, resulting from theYoung-Laplace pressure at highly curved liquid menisci, quantitatively accountsfor a downward-shift of the P-N transition and an increased molecular mobilityin comparison to the unstretched liquid state of the complete filling. Thestrengths of the slow and fast relaxations provide local information on theorientational order: The thermotropic behaviour in the core region isbulk-like, i.e. it is characterized by an abrupt onset of the nematic order atthe P-N transition. By contrast, the interface ordering exhibits a continuousevolution at the P-N transition. Thus, the phase behaviour of the entirelyfilled liquid crystal-silica nanocomposite can be quantitatively described by alinear superposition of these distinct nematic order contributions.

Inhomogeneous Relaxation Dynamics and Phase Behaviour of a Liquid Crystal Confined in a Nanoporous Solid