title: Paranematic-to-nematic ordering of a binary mixture of rodlike liquid crystals confined in cylindrical nanochannels.
abstract: We explore the optical birefringence of the nematic binary mixtures 6CB_{1-x}7CB_{x} (0 ≤ x ≤ 1) embedded into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of 3.4 ≤ R ≤ 21.0 nm. The results are compared with the bulk behavior and analyzed with a Landau-de Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field σ<1/2) or continuously (overcritical regime, σ>1/2), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction x and scales inversely proportionally with R for channel radii larger than 4 nm. The critical pore radius, R_{c}, separating a continuous from a discontinuous paranematic-to-nematic evolution varies linearly with x and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point T_{PN} and of the nematic ordering field σ versus x suggests that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than ∼7 nm.
authors.affiliation: Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
authors.forename: Sylwia
authors.initials: S
authors.lastname: Całus
authors.affiliation: Faculty of Environmental Engineering and Biotechnology, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Jabłońska
authors.affiliation: Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Busch
authors.affiliation: FR 7.2 Experimental Physics, Saarland University, D-66123 Saarbrücken, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rau
authors.affiliation: Materials Physics and Technology, Hamburg University of Technology (TUHH), D-21073 Hamburg-Harburg, Germany and FR 7.2 Experimental Physics, Saarland University, D-66123 Saarbrücken, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Huber
authors.affiliation: Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
authors.forename: Andriy V
authors.initials: AV
authors.lastname: Kityk
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D050866:Liquid Crystals / Q000737:chemistry*; D044085:Microfluidics / Q000379:methods; D008956:Models, Chemical; D008958:Models, Molecular; D058608:Nanopores / Q000648:ultrastructure; D043942:Nanotubes / Q000737:chemistry* / Q000648:ultrastructure*; D044367:Phase Transition; D012031:Refractometry / Q000379:methods*; D012822:Silicon Dioxide / Q000737:chemistry
chemical_list: D012822:Silicon Dioxide; D000537:Aluminum Oxide