Effects of interactions with the surface on the orientation of the mesogenic monoazacrown-substituted phthalocyanine films

In this paper, the effect of interaction with the substrate surface on the orientation of films' molecules of substituted liquid crystalline phthalocyanines M(II)Pc (M = Cu, Ni, Zn) having monoazacrown ether moieties on the periphery containing long alkyloxyphenyl N-pivotal groups is studied. The phthalocyanine derivatives demonstrate thermotropic mesophase behaviour and show Col_h mesophases over a wide temperature range. The preferential orientation of the phthalocyanine films deposited on glass, silicon and NaCl substrates as well as between two of those substrates is studied by polarized Raman spectroscopy at different temperatures. These phthalocyanines form homeotropically aligned films on the surface of NaCl substrate, whereas planar alignment with a random distribution of the column directors occurs on the glass slides.     

Wide view supertwisted nematic liquid-crystal light shutter

We present a novel concept of a wide viewing angle liquid-crystal display (LCD) light shutter, taking advantage of the highly symmetric 180 degrees -twisted liquid-crystal (LC) configuration and the light propagation starting with a single mode. In a specific case of the high voltage driven LCD light shutter, the resulting very high overall symmetry allows for the efficient angular compensation of the light attenuation in the optically closed state using just a simple, specifically tuned, negative-birefringent c-plate retarder. The latter can be adapted to compensate for the positive optical birefringence of the homeotropically aligned LC molecules as well as also for a great deal of the angular dependence of the crossed polarizers. We show that the additional partial compensation of the angular dependence of the crossed polarizers can be explained by a combined effect of the positive birefringence of the homeotropically aligned LC molecules, negative-birefringence c-plate retarder, and an in-plane residual positive birefringence (a-plate) of the boundary layers of the LC molecules.     

Spatially periodic deformation of a nematic liquid crystal caused by flows near a microcontact in an asymmetric cell

It has been experimentally established for the first time that a steady-state spatially periodic deformation of the director field with an electrically controlled period is formed near a microcontact in a homeotropically oriented 5CB nematic liquid crystal. The periodic distribution of the director is due to its orientation by counterpropagating flows of the nematic material and the wave-shaped profile of the boundary layer.     

The driving force for homeotropic alignment of a triphenylene derivative in a hexagonal columnar mesophase on single substrates

An interesting discotic triphenylene derivative, 2,7-biscarbethoxy-3,6,10,11-tetrapentyloxytriphenylene, can be homeotropically aligned on a large scale as a film on single substrates, i.e. the film with one side on the substrate and the other side freestanding. The alignment is achieved in a controlled condition close to a thermodynamic equilibrium state in a liquid crystal phase when interactions at the substrate surface are limited. Phase changing properties of this material are also a key factor in the alignment processes. The aligned structures are observed with an optical microscope. Within a single domain a hexagonal lattice of a d-spacing 16.3 Å is confirmed by X-ray diffraction measurement.     

Diffraction light modulator based on transverse electro-optic effect in short-pitch ferroelectric liquid crystals

A diffraction modulator that exploits the transverse electro-optic effect in ferroelectric liquid crystals is proposed for applications in displays and in spatial light modulators. Experiments with a short-pitch ferroelectric liquid crystal aligned homeotropically show an achromatic contrast ratio of greater than 100:1 available with oblique readout. The sources of the contrast deterioration and the tolerance of the proposed scheme to this deterioration are analyzed. For selected directions of readout the light output obtains low sensitivity to the polarization of the readout light. Nonlaser light sources can be used in a practical display setup based on the proposed principle.     

The dynamics of the response of an electro-optic cell based on a nematic layer with controlled surface anchoring

We investigate the electrooptical characteristics of a cell based on a nematic liquid crystal layer controlled with the use of modification of the surface anchoring by an ionic surfactant. The inverse mode of the effect is used with the nematic oriented homeotropically in the initial state and transferring to the hybrid homeoplanar structure in an applied dc electric field. We consider the applied voltage dependences of the dynamic parameters of the optical response.     

Orientational control of liquid crystal molecules by reformed poly(dimethylsiloxane) alignment layer via ion-beam irradiation

We introduce an alternative approach to making a reformed PDMS layer as a pretilt controllable alignment layer, which can be used in the vertical alignment (VA) and twisted nematic (TN) modes, by varying the ion beam (IB) energy. Depending on different the dielectric anisotropy of surfaces, PDMS layers have been demonstrated to align LC molecules homogeneously and homeotropically. The electro-optic characteristics of aligned VA and TN-LCD based on PDMS layer were comparable to those of VA and TN-LCD based on polyimide, showing good potential of PDMS film as an alignment layer.     

Cover Picture: Functionalized Gold Nanoparticles Mimic Catalytic Activity of a Polysiloxane‐Synthesizing Enzyme (Adv. Mater. 10/2005)

A system that acts as a biomimetic of the silica‐synthesizing enzyme found in a marine sponge is reported by Morse and co‐workers on p. 1234. Gold nanoparticles (GNPs) are functionalized with the same organic moieties that are found in the enzyme's catalytic site. Interaction between the nucleophilic (OH‐terminated) and hydrogen‐bonding (imidazole‐terminated) GNPs, as shown on the cover, is required for the hydrolysis of a silicon alkoxide precursor and subsequent polycondensation to form silica at a low temperature and near‐neutral pH. Replacement of either of the required functional groups by a non‐reactive methyl group abolishes catalysis in this synthetic system, as it does in the biological enzyme. Cover art provided by Peter Allen.     

Cover Picture: Long,Monomolecular Guanine‐Based Nanowires (Adv. Mater. 15/2005)

The cover picture is an artistic view, designed by Noam Hamou, of a G‐wire, probably a G4‐DNA nanowire, where the schematic spiral and tetrad are emerging from a single molecule deposited on a mica surface, as imaged by AFM. Kotlyar and co‐workers report on p. 1901 on the development of novel long monomolecular G‐wires that, upon self‐folding, form structures of consecutive guanine tetrads with and without metal ions in the inner channel of the molecule. The continuity of the molecule backbone and its improved stiffness suggest that this single DNA‐based structure might be useful for nanoelectronic applications.     

Thermomechanical effect in a hybrid-oriented nematic liquid crystal

The first experimental observation of a thermomechanical effect in a homeotropically planaroriented nematic liquid crystal is reported. The effect consists of the appearance of a hydrodynamic flow induced by a longitudinal temperature gradient. The measured value of the thermomechanical coefficient agrees well with the theoretical estimate. Pis’ma Zh. Tekh. Fiz. 23, 77–81 (September 12, 1997)     

Flexoelectric response of a liquid crystal layer with a temperature-induced orientational transition

It has been confirmed that the flexoelectric polarization model can provide an adequate interpretation of the temperature behavior of the electrical response of homeotropically oriented samples of n-methoxybenzylidene-n-butylaniline nematic liquid crystals at twice the excitation frequency. The temperature dependence of samples with different director orientations has been investigated experimentally. Pis’ma Zh. Tekh. Fiz. 23, 19–23 (May 12, 1997)     

Acousto-optical effect induced by ultrasound pulses in a nematic liquid-crystal film

The reorientation of the director of a homeotropically aligned nematic liquid-crystal film subjected to ultrasound pulses is discussed. The relationship is investigated for the first time, to our knowledge, between the transmitted optical power and the high-frequency (approximately megahertz) pulsed ultrasound intensity. It is evident that there exists a power law governing the ultrasound-intensity-dependent optical transmission. However, the data indicate no existence of a characteristic threshold for the acousto-optical effect. Our results suggest that acoustic streaming, known to be responsible for acousto-optical effects in cw ultrasound experiments, should also play a similarly important role in the case involving a pulsed ultrasound field.     

Inside Front Cover: Construction of Chiral Propeller Architectures from Achiral Molecules (Adv. Mater. 24/2006)

Chiral propeller architectures constructed from achiral molecules via hydrogen bonding self‐assembly, in addition to Frank–Pryce spherulitic droplet and fingerprint textures, are reported on p. 3229 by Cheng and co‐workers. It is found, for the first time, that neither molecular chirality nor a molecular bend is necessary to form a chiral phase, which is of particular interest for next‐generation biological and electro‐optical materials science and technology.     

A functionally separated nanoimprinting material tailored for homeotropic liquid crystal alignment

In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processed by nanoimprint lithography technology (NIL), we propose to design a hybrid-type homeotropic polymer material consisting of two distinct moieties with largely different thermo-mechanical properties and surface activity. Surface contact angle measurements and sum-frequency vibrational spectroscopy allow us to conclude that the polymer film is a functionally separated composite suitable for the homeotropic LC alignment processed by NIL. As one of the potential applications using the hybrid-type homeotropic polymer, we demonstrate that the nanoimprinted grooves at the polymer surface can achieve a zenithal nematic LC bistability.     

Cover Picture: Acceleration of Calcite Kinetics by Abalone Nacre Proteins (Adv. Mater. 22/2005)

Abalone utilizes a system of macromolecular matrices and soluble proteins to produce beautiful and mechanically robust shells. The cover shows work by Qiu and co‐workers reported on p. 2678, in which AP8 proteins isolated from the shell of red abalone are shown to alter the growth of calcite both by accelerating the rate and modifying the shape from the simple rhombohedra seen in the upper left of the scheme to the more complex form seem in the lower right. The changes are made manifest at an atomic scale through alterations in the growth speed and shape of the atomic steps that form the growth hillocks (background).     

Cover Picture: Programmable Motion and Separation of Single Magnetic Particles on Patterned Magnetic Surfaces (Adv. Mater. 14/2005)

Structured magnetic surfaces enabling programmable motion of single micrometer‐sized magnetic particles are reported on p. 1730 by Gunnarsson and co‐workers. Patterns of thin‐film magnetic elements are tailored to form transport lines with junctions for the separation of individual particles. This method has the potential to improve and generate new applications in biotechnology. The cover shows a schematic of the transportation and separation of magnetic particles functionalized with antibodies capable of selectively capturing the corresponding analytes from a sample.     

Simulation of the viewing properties and optical compensation of the biaxial nematic in-plane switching mode

Using Berreman 4 × 4 optical methods and continuum theory, we investigate the theoretical viewing properties of a potential homeotropically aligned biaxial nematic display switched with in-plane fields. We determine the isocontrast, isotransmission viewing characteristics for wide-angle viewing for in-plane switching and consider the necessary requirements for optical compensation to produce a high transmission in the bright state and low transmission in the dark state. We show how compensation can be achieved with biaxial compensation layers using a homogeneous biaxial film or from birefringence.