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Item type:Publication, Access status: without files , Mesoporous alumina- and silica-based crystalline nanocomposites with tailored anisotropy: Methodology, structure and propertiesWe present several recently synthesized nanocomposites consisting of liquid crystals as well as an organic molecular crystal embedded into the nanochannels of mesoporous alumina and silica. As liquid-crystalline mesogens achiral, nematogen and chiral cholesteric guest molecules infiltrated into nanochannels by spontaneous imbibition were chosen. The molecular ordering inside the nanochannels, which can be tailored by modifying the surface anchoring, was characterized by optical polarimetry (linear and/or circular birefringence) in combination with X-ray diffraction. For the synthesis of the solid crystalline nanocomposites ferroelectric triglycine sulfate (TGS) nanocrystals were deposited into the nanochannels by slow evaporation of saturated water solutions imbibed into the porous hosts. Their textural and physicochemical properties were explored by x-ray diffraction, scanning electron microscopy and dielectric techniques.Publicationtype: Conference Paper148 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Molecular ordering of nematic liquid crystals in tubular nanopores: Tailoring of optical anisotropy at the nanoscale by polymer pore-surface graftingThe optical polarimetry technique is used to explore molecular ordering of nematic liquid crystals 5FPFFPP3 embedded in parallel cylindrical channels of alumina membranes with pore walls covered by a SE-1211 polymer film enhancing normal anchoring. A chemical film deposition from organic solution apparently results in inhomogeneous coverage with local islands on the channels walls. Accordingly, a coexistence of differently ordered LC regions (nanodomains), characterized by positive and negative anisotropy, results in a weak effective (average) optical birefringence. Repeated polymer deposition reduces the size of uncovered pore walls regions and thus leads to a strengthening of negative optical anisotropy observed in the experiments.Publicationtype: Conference Paper59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Application of retardation-modulation polarimetry in studies of nanocomposite materials(2018-04-10); ; ; ; We demonstrate an application of retardation-modulation polarimetry in studies of nanocomposite materials. Molecular ordering is explored on both nonchiral and chiral liquid crystals (LCs) in the bulk state and embedded into parallel-arrays of cylindrical channels of alumina or silica membranes of different channel sizes (12-42 nm). Two arms polarimetry serves for simultaneous measurements of the birefringence retardation and optical activity characterizing, respectively, orientational molecular ordering and chiral structuring inside nanochannels.Publicationtype: Conference Paper125 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A ferroelectric liquid crystal confined in cylindrical nanopores : reversible smectic layer buckling, enhanced light rotation and extremely fast electro-optically active Goldstone excitations(Royal Society of Chemistry (RSC), 2017-11-27); ; ; ; The orientational and translational order of a thermotropic ferroelectric liquid crystal (2MBOCBC) imbibed in self-organized, parallel, cylindrical pores with radii of 10, 15, or 20 nm in anodic aluminium oxide monoliths (AAO) are explored by high-resolution linear and circular optical birefringence as well as neutron diffraction texture analysis. The results are compared to experiments on the bulk system. The native oxidic pore walls do not provide a stable smectogen wall anchoring. By contrast, a polymeric wall grafting enforcing planar molecular anchoring results in a thermal-history independent formation of smectic C* helices and a reversible chevron-like layer buckling. An enhancement of the optical rotatory power by up to one order of magnitude of the confined compared to the bulk liquid crystal is traced to the pretransitional formation of helical structures at the smectic-A*-to-smectic-C* transformation. A linear electro-optical birefringence effect evidences collective fluctuations in the molecular tilt vector direction along the confined helical superstructures, i.e. the Goldstone phason excitations typical of the para-to-ferroelectric transition. Their relaxation frequencies increase with the square of the inverse pore radii as characteristic of plane-wave excitations and are two orders of magnitude larger than in the bulk, evidencing an exceptionally fast electro-optical functionality of the liquid-crystalline-AAO nanohybrids.Publicationtype: Journal ArticleScopus© Citations 25 399 535 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Chiral Phases of a Confined Cholesteric Liquid Crystal: Anchoring-Dependent Helical and Smectic Self-Assembly in Nanochannels(2016-06-02); ; ; ; Chiral liquid crystals (ChLCs) allow a fundamental insight into the interplay of molecular chirality and the formation of macroscopic, self-assembled helices. They also exhibit unique optical properties, in particular huge polarization rotation, which is employed in a wide range of photonic technologies. Here, we present a study of linear and circular optical birefringence in combination with X-ray diffraction experiments on an archetypical ChLC, i.e., the cholesteric ester CE6, confined in cylinders of mesoporous alumina and silica with distinct polymer surface graftings resulting in normal or tangential wall anchoring. The unconfined ChLC exhibits a discontinuous, first-order isotropic-to-chiral nematic (cholesteric) phase transition with the formation of double-twist helices and a discontinuous cholesteric-to-smectic A transition. The thermotropic behavior of the confined ChLC, explored in a channel radii range of 7-21 nm, deviates substantially from bulk behavior. There is no isotropic state. In contrast, a chiral paranematic phase with a preferred arrangement of the ChLC at the channel wall is found. For normal anchoring, a radial-escape structure evolves upon cooling. The phase transition to the smectic phase is completely suppressed. For tangential anchoring, a large optical activity indicates a continuous paranematic-to-cholesteric transition with double-twist helices aligned parallel to the long axes of the cylinders. Upon cooling, these helical structures, known as basic building blocks of blue ChLC phases, transform in a continuous manner to a cylinder-aligned smectic A phase.Publicationtype: Journal Article78