Issue 8, 2012

Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

Abstract

The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature Tc is dominated by smectic elastic compressibility distortions. The observed anomalous Tc(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1st order I-SmA phase transition tends to be replaced by a 2nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.

Graphical abstract: Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

Article information

Article type
Paper
Submitted
03 Oct 2011
Accepted
18 Nov 2011
First published
18 Jan 2012

Soft Matter, 2012,8, 2460-2470

Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

S. Kralj, G. Cordoyiannis, D. Jesenek, A. Zidanšek, G. Lahajnar, N. Novak, H. Amenitsch and Z. Kutnjak, Soft Matter, 2012, 8, 2460 DOI: 10.1039/C1SM06884A

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