F. Schneider

Bio: F. Schneider is an academic researcher from Folkwang University of the Arts. The author has contributed to research in topics: Liquid crystal & Rotational viscosity. The author has an hindex of 12, co-authored 33 publications receiving 479 citations. Previous affiliations of F. Schneider include Technical University of Berlin.

Determination of the Viscosity Coefficients of the Liquid Crystal MBBA

Abstract: An experimental procedure is described which allows the determination of the viscosity coefficients η1, η2, η3 and η12 for nematic liquid crystals as a function of temperature. Errors which arise from the surface and the flow alignment are discussed in detail. The measurements are performed on the nematic liquid crystal 4-methoxybenzylidene-4'-n-butyl-aniline (MBBA). At 25°C the viscosity coefficients are η1 = 0.1361, η2 = 0.0240, η3 = 0.0413 and η12 = -0.0181 Pa s.

Induced smectic phases

Abstract: Mixtures of terminal polar with terminal non-polar nematic liquid crystals usually produce induced smectic phases (ISP). This is shown by the investigation of a great number of systems using the contact method.In general, SA phases are induced. By means of X-ray investigations SB and SE phases were also established. No solid molecular complex was found. The layer spacing for the induced smectic phases becomes minimal for mixtures about 1 : 1 at which the maximum thermal stability of the induced smectic phases was found as well. The effects observed indicate a close relation between the induction of smectic phases and the formation of the double layer structure in the smectic phases of terminal polar liquid crystals.

Reentrant Nematic Mixtures

Abstract: Binary mixtures of some terminal non-polar liquid crystals with the two terminal polar liquid crystals 4-cyano-4′-n-octyloxy-biphenyl (8 CBP) and 4-cyano-benzylidene-4′-n-octyloxyaniline (CBOOA) exhibit reentrant nematic phases. The phase diagram of the system 8 CBP/CBOOA indicates that the pure components show this effect too. X-ray data on layer thickness and transition enthalpies are presented.

Rotational viscosity of nematic liquid crystals and their shear viscosity under flow alignment

Abstract: The influence of molecular properties on the rotational viscosity, γ1, of nematic liquid crystals is studied. The shear viscosity under flow alignment, ηs, is determined for the same liquid crystals. A significant correlation between both quantities is found. An equation is presented which allows the calculation of γ1 from ηs with an error of about 20 per cent for the liquid crystals studied.

Flow of a Nematic Liquid Crystal Around a Sphere

Abstract: The flow of an incompressible nematic liquid crystal around a sphere is studied for arbitrary angles between the director and the flow velocity at infinite distances. We assume low Reynolds numbers and a fixed director orientation for the calculation on the basis of the Leslie-Ericksen equations. The calculations are performed with a finite difference method which is a combination of the artificial compressibility method for the pressure determination and a simultaneous over-relaxation (SOR, SSOR) for the solution of the momentum equations. We find strong differences in the stream line patterns of a usual liquid crystal as compared with those of an isotropic liquid if the direction of the director is perpendicular to the flow velocity. The force on the sphere is calculated. Equations are presented which allow the determination of the force for a broad range of anisotropies of the viscosity coefficients. The falling direction of a sphere deviates from the direction of gravity by 25° for a liquid c...

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Abstract: 6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Recent Advances in Singlet Fission

Abstract: A survey is provided of recent progress in the understanding of singlet fission, a spin-allowed process in which a singlet excited molecule shares its energy with a ground-state neighbor to produce two triplet excited molecules. It has been observed to occur in single-crystal, polycrystalline, and amorphous solids, on timescales from 80 fs to 25 ps, producing triplet yields as high as 200%. Photovoltaic devices using the effect have shown external quantum efficiencies in excess of 100%. Almost all the efficient materials are alternant hydrocarbons of the acene series or their simple derivatives, and it is argued that a wider structural variety would be desirable. The current state of the development of molecular structure design rules, based on first-principles theoretical considerations, is described along with initial examples of implementation.

Rotational viscosity γ1 of nematic liquid crystals

Abstract: The rotational viscosity coefficients γ1 are measured with the rotating field method as a function of temperature in the nematic phases of 4‐methoxybenzylidene‐4′‐n‐butylaniline, 4‐n‐pentyl‐, and 4‐n‐octyl‐4′‐cyanobiphenyl, of the eutectic mixture of two 4‐n‐pentylphenyl 4‐alkoxybenzoates and of the eutectic mixture of the two isomers of 4‐methoxy‐4′‐n‐butylazoxybenzene. Equations are proposed which describe the temperature dependence very well. The Leslie coefficients αi are calculated from the γ1 values and recently measured shear viscosity coefficients.