Thermodynamically Anchoring-Frustrated Surface to Trigger Bulk Discontinuous Orientational Transition.

Surface-specific liquid crystal (LC) nanostructures provide a unique platform for studying surface-wetting phenomena and also for technological applications. The most important studies on LC properties are related to bulk alignment, surface anchoring, and so on. Here, we study an LC system with a nematic liquid crystal (NLC) on a perfluoropolymer-coated substrate, in which a discontinuous bulk orientational transition has recently been found.

Stepwise heat-capacity change at an orientation transition in liquid crystals.

During a phase transition in a bulk material, heat is exchanged with matter to balance the changes in the internal energy and the entropy of the system. Here we report on the thermal detection of a surface-mediated anchoring transition, a spontaneous and discontinuous orientation change between planar (P) and homeotropic (H) alignments within a single nematic phase by changing temperature. In this case a stepwise change in the heat flow, similar to a glass transition, is observed by means of high-resolution differential scanning calorimetry.

Local orientational analysis of helical filaments and nematic director in a nanoscale phase separation composed of rod-like and bent-core liquid Crystals using small- and wide-angle X-ray microbeam scattering.

We analyzed the local nanostructure in binary mixtures of rod- and bent-shaped molecules, n-pentyl-4-cyanobiphenyl (5CB) and 1,3-phenylene bis[4-(4-n-octyloxyphenyliminomethyl) benzoates] (P-8-OPIMB), respectively, using small- and wide-angle X-ray microbeam and macrobeam scattering. From the orientational X-ray scattering patterns, we concluded that the nematic director of 5CB is almost parallel to the smectic layers dominated by bent-core molecules in Bx. Moreover, we observed oriented small-angle diffraction peaks (about 300 Å), which is close to the spacing of 5-7 layers, and also consistent with the width of a helical nanofilament textures as observed by freeze-fracture transmission electron microscopy.

Critical anomalies in thermal diffusivity of liquid-crystalline terephthal-bis-(4-n-butylaniline).

A temperature wave method has been applied to observe the thermal diffusivity through the isotropic (Iso)-nematic (N)-smectic Sm-A-Sm-C-Sm-B-crystals VI-VII-VIII phase transitions of terephthal-bis-(4-n-butylaniline) (TBBA). Critical anomalies have been found in the N-Sm-A and Sm-C-Sm-B phase transitions as diplike shaped, consistent with the predictions based on the dissipative couplings between the order parameter and the conserved free-energy density. Singular points with a gap have been observed at the Sm-B-crystal VI, crystals VI-VII, and crystals VII-VIII phase transitions, which show polymorphic behaviors on heating and cooling.

Two transitions between isotropic and nematic phases in confined liquid crystals.

The molecular mean-field theory for the nematic-isotropic (N-Iso) phase transition in the vicinity of the surface is derived. We have shown that the nematic order parameter in liquid crystal near the surface is generally different from that in the bulk. It is never equal to zero if the anisotropic interaction with the surface is present.

Isotropic-nematic transition at the surface of a liquid crystal embedded in an aerosil network.

We reexamined the isotropic-nematic (Iso-N) phase transitions of 4-n-heptyl cyanobiphenyl (7CB) embedded in aerosils of silica nanoparticle dispersions using highly sensitive differential scanning calorimetry (HS-DSC), polarizing optical microscopy (POM), and retardation measurements. We found a simple and very profound relationship between the calorimetric and optical measurements; in addition to double DSC peaks, which have been observed previously, a two-step change of the retardation was clearly observed by varying temperature. From our analysis, there is no doubt that the Iso-N liquid-crystal phase transition certainly occurs in two steps, i.

Observation of two isotropic-nematic phase transitions near a surface.

Using specified conditions, we succeeded in observing the isotropic-nematic (Iso-N) liquid crystal phase transition at surfaces followed by that in bulk for the first time. An additional heat anomaly peak was found at a higher temperature side of a main phase transition peak using highly sensitive differential scanning calorimetry (HS-DSC). The peak is pronounced particularly in the cooling process, since the transition starts at surfaces on cooling.