Werner E. L. Haas

Interaction Between UV Radiation and Cholesteric Liquid Crystals

Abstract Mixtures of cholesteryl iodide and cholesteryl bromide with cholesteryl nonanoafce were exposed to UV radiation and the resultant color shifts were measured as a function of exposure and composition. The formation of images by this process will be described, and the presiding mechanism will be briefly discussed.

Characterization of Molecular Role in Pitch Determination in Liquid Crystal Mixtures

Abstract Pitch versus composition data in a binary mixture of a cholesteric and a room-temperature nematic are used to demonstrate that molecular influence in pitch determination is more linear when credited according to weight percent than when credited according to mole %. It is also shown that the effective rotary power of cholesteryl iodide is influenced by its environment to the extent that it exhibits the chirality of the other constituent in a binary mixture.

Cholesteric Films as Optical Filters

A new class of large‐area optical filters based on the special reflection properties of cholesteric liquid crystals is described. Several filtering functions are provided by various combinations of liquid‐crystal films, polarizers, and retardation plates.

Electric-Field Induced Phase Change in Cholesteric Liquid Crystals

Abstract Optically-negative cholesteric liquid-crystal films can be transformed to an optically-positive state by applying high d-c electric fields. A phase transformation occurs in which the helicoidal cholesteric structure is converted to either a planar smectic, or a linear nematic, structure. The threshhold field for this transformation has been studied as a function of sample thickness, temperature and composition. Bulk fields are responsible for the phenomenon. It is inferred that the compositional dependences are due to size factors and internal molecular dipole moments.

Electrically variable diffraction in spherulitic liquid crystals

An electrically controllable diffraction mode in liquid crystals is described. The variable grating is a stable single layer of small uniform birefringent spherulitic domains imbedded in a homeotropic matrix. The size of the domains is changed by small dc or ac voltages.

Topology of obliquely coated silicon monoxide layers

Silicon monoxide layers, coated at oblique angles of 45°–87° onto indium oxide coated glass substrates, are examined by TEM for angularly dependent surface topology. ’’Striations’’ observed at angles near 81° are discussed in terms of the aligning influence that these features exert upon nematic liquid crystals. Included are photomicrographs of these striations as well as of a ’’scale’’ feature observed at angles greater than 83°. Existence of the ’’scale’’ feature is correlated to previously observed asymmetric diffuse diffraction effects.

Optical storage effects in liquid crystals

Abstract The electro-optic behavior of two chemically identical liquid crystal mixtures was compared. It was determined that ethoxybenzylidene- p ′- n -butylaniline (Eobuta) doped with 10% 1-methanol exhibited pronounced optical storage, whereas Eobuta doped with 10% racemic menthol only exhibited dynamic scattering. Since Eobuta doped with 1-menthol is cholesteric and Eobuta doped with racemic menthol is nematic, it was concluded that optical storage capability is an intrinsic property of the cholesteric state, and in agreement with the observable textures, should be viewed as a reversible plane ⇄ focal-canic texture change.

Liquid Crystal adiSplay Research: The First Fifteen Years

Abstract This paper is a reveiw of thmore sinigicant developments in the liquid crystal display field during the last fifteen years. Major effects and their applications are discussed, and the state-of-the-art is presented.

Pitch Dependence on Composition in Mixtures of Liquid Crystals

Abstract The linear additive law for pitch dependence in binary mixtures of cholesterics (or combinations of ingredients producing cholesterics) is extended to include first order interactive effects. The resulting expression is shown to effectively treat an apparently widely diverse collection of experimental data. The knowledge of the functional form of any given system is of value in predicting pitch sensitivity to heat, vapor, etc.

Light Scattering Properties of Cholesteric Liquid Crystal Films

Abstract It has been observed that cholesteric liquid crystal films exist in two states both of which exhibit characteristic brilliant colors. A transition between the two states can be caused by a variety of disturbances including mechanical perturbation and electrophoretic action.1 Optical scattering data indicate that the fundamental dispersive cause in both the undisturbed state and the disturbed state is the existence of regions of local order characterized by optically anisotropic layers stacked in a helical fashion. Intensity studies indicate that the angular distribution of helical axes is not isotropic in either state. In the undisturbed state the helical axes lie predominantly in the plane of the surface whereas in the disturbed state the helical axes are predominantly normal to the surface. This is confirmed by microscopic observations which show in the undisturbed state regions (with the dimensions of microns) of large birefringence and no optical activity. The disturbed state exhibits one uni...