Thermotropic nematic order upon nano-capillary filling

Abstract

Optical birefringence and light absorption measurements reveal four regimes for the thermotropic behavior of a nematogen liquid (7CB) upon sequential filling of parallel-aligned capillaries of 12 nm diameter in a monolithic, mesoporous silica membrane. No molecular reorientation is observed for the first adsorbed monolayer. In the film-condensed state (up to 1 nm thickness) a weak, continuous paranematic-to-nematic (P-N) transition is found, which is shifted by 10 K below the discontinuous bulk transition at T_IN=305K. The capillary-condensed state exhibits a more pronounced, albeit still continuous P-N reordering, located 4 K below T_IN. This shift vanishes abruptly on complete filling of the capillaries, which we tentatively trace to a 10 MPa tensile pressure release associated with the disappearance of concave menisci in the confined liquid.

6 pages, 3 figures

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• Inhomogeneous Relaxation Dynamics and Phase Behaviour of a Liquid Crystal Confined in a Nanoporous Solid
• High-resolution dielectric study reveals pore size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores
• Adsorption from Binary Liquid Solutions into Mesoporous Silica: A Capacitance Isotherm on 5CB Nematogen/Methanol Mixtures