Effect of polymer concentration on stabilized large-tilt-angle flexoelectro-optic switching

In this letter, the uniform lying helix (ULH) liquid crystal texture, required for the flexoelectro-optic effect, is polymer stabilized by the addition of a small percentage of reactive mesogen to a high-tilt-angle (φ>60°) bimesogenic chiral nematic host. The electro-optic response is measured for a range of reactive mesogen concentration mixtures, and compared to the large-tilt-angle switch of the pure chiral nematic mixture. The optimum concentration of reactive mesogen, which is found to provide ample stabilization of the texture with minimal impact on the electro-optic response, is found to be approximately 3%. Our results indicate that polymer stabilization of the ULH texture using a very low concentration of reactive mesogen is a reliable way of ruggedizing flexoelectro-optic devices without interfering significantly with the electro-optics of the effect, negating the need for complicated surface alignment patterns or surface-only polymerization. The polymer stabilization is shown to reduce the temperature dependence of the flexoelectro-optic response due to "pinning" of the chiral nematic helical pitch. This is a restriction of the characteristic thermochromic behavior of the chiral nematic. Furthermore, selection of the temperature at which the sample is ultraviolet cured allows the tilt angle to be optimized for the entire chiral nematic temperature range. The response time, however, remains more sensitive to operating temperature than curing temperature. This allows the sample to be cured at low temperature and operated at high temperature, providing simultaneous optimization of these two previously antagonistic performance aspects. © 2006 American Institute of Physics.

High tilt angle FLC SLM for optical interconnects

The use of high tilt angle FLC SLM for optical interconnects was discussed. The transmissive SLM was designed as a 320×1 pixels glass SLM with 20 μm pitch pixels and 2 μm pixel deadspace. The SLM was fabricated using standard class 100 cleanroom facilities to make a glass on glass 1D SLM. The results show that a N×N optical switch can be built using the two-hologram architecture.

Micro-electro-mechanical resonant tilt sensor

This paper reports a micro-electro-mechanical tilt sensor based on resonant sensing principles. The tilt sensor measures orientation by sensing the component of gravitational acceleration along a specified input axis. Design aspects of the tilt sensor are first introduced and a design trade-off between sensitivity, resolution and robustness is addressed. A prototype sensor is microfabricated in a foundry process. The sensor is characterized to validate predictive analytical and FEA models of performance. The prototype is tested over tilt angles ranging over ±90 degrees and the linearity of the sensor is found to be better than 1.4% over the tilt angle range of ±20°. The noise-limited resolution of the sensor is found to be approximately 0.00026 degrees for an integration time of 0.6 seconds. © 2012 IEEE.

Sources of variability in the free-ball micro-scale abrasion test

In the 'free-ball' version of the micro-scale abrasion or ball-cratering test the rotating ball rests against a tilted sample and a grooved drive shaft. Tests under nominally identical conditions with different apparatus commonly show small but significant differences in measured wear rate. An indirect method has been developed and demonstrated for continuous on-line measurement of the coefficient of friction in the free-ball test. Experimental investigation of the effects of sample tilt angle and drive shaft groove width shows that both these factors influence the stability of the rotation of the ball, and the shape of the abrasive slurry pool, which in turn affect the coefficient of friction in the wear scar area and the measured wear rate. It is suggested that in order to improve the reproducibility of this method the geometry of the apparatus should be specified. For the apparatus used in this work with a steel ball of 25 mm diameter, a sample tilt angle of 60-75° and a shaft groove width of about 10mm provided the most stable ball motion and a wear rate which showed least variability. © 2004 Elsevier B.V. All rights reserved.

Synthesis and properties of a new series of low-molar-mass organo-siloxane derivatives

Two series of ferroelectric liquid crystalline organo-siloxanes containing a laterally attached halogen on the phenyl ring have been synthesised and characterised to determine the impact of the siloxane group and the halogen on the mesomorphism and electro-optic switching properties. Both monomesogenic and bimesogenic compounds have been studied. The monomesogenic derivatives were found to be ferroelectric with high tilt and Ps. The tilt angle of 45° and the Ps of 95nC/cm2 are almost temperature independent. The bimesogenic bromo substituted derivatives showed mainly ferroelectric phases about 60°C wide. Maximum values for the spontaneous polarisation and the tilt angle were only slightly influenced by the length of the siloxane spacer. Altering the halogen to a fluorine shifted the liquid cystalline phase slightly to higher temperatures whilst maintaining the mesophase range of 60°C.

New chiral E- and Z-isomers of the 1R,4R-2-arylidene-p-menthane-3-ones in induced cholesteric and ferroelectric liquid crystals

A novel pair of the E- and Z-isomeric 1R,4R-2-(4-heptyloxyphenyl)-benzylidene-p-menthan-3-ones has been prepared and the influence of distinctions in their molecular geometry on macroscopic properties of liquid crystal systems with the induced supra-molecular helical structure has been studied. The significantly lower helical twisting power of the chiral Z-isomer in comparison with that of E- one has been confirmed in the case of induced cholesteric systems based on 4-pentyl-4-cyanobiphenyl. The phase behavior and ferroelectric characteristics have been investigated for smectic-C* compositions based on the eutectic mixture of the homological 4-hexyloxyphenyl-4'-hexyloxy- and 4-hexyloxyphenyl-4'-octyloxybenzoates containing the novel isomeric chiral dopants. The spontaneous polarisation of the opposite signs induced by the isomeric chiral components has been revealed for the compositions studied. Distinctions in phase states, absolute values of the spontaneous polarization, smectic tilt angle and rotation viscosity of the systems obtained are discussed.

Ferroelectric liquid crystal mixtures containing chiral ether and ester compounds with the 2-arylidene-p-menthan-3-one skeleton

Some 1R,4R-2-(4-phenylbenzylidene)-p-menthane-3-one derivatives containing the ether or ester linking group between benzene rings of the arylidene fragment have been studied as chiral dopants in ferroelectric liquid crystal systems based on the eutectic mixture (1:1) of two phenylbenzoate derivatives CmH2m+1OC6H4COOC6 H4OCnH2n+1 (n = 6; m = 8, 10). The ferroelectric properties of these compositions (spontaneous polarization, rotation viscosity, smectic tilt angle as well as quantitative characteristics of their concentration dependences) were compared with those for systems including chiral dopants containing no linking group. Ferroelectric parameters of the induced ferroelectric compositions studied have been shown to depend essentially on the presence of the linking group between benzene rings and its nature as well as on the number of the benzene rings in the rigid molecular core of the chiral dopants used. For all ferroelectric liquid crystal systems studied, the influence of the chiral dopants on the thermal stability of N*, SmA and SmC* mesophases has been quantified. The influence of the linking group nature in the dopant molecules on the characteristics of the systems studied is discussed taking into account results of the conformational analysis carried out by the semi-empirical AM1 and PM3 methods.

Low Molar Mass Organosiloxane Liquid Crystalline Dyes for Dye Guest Host Ferroelectric Display Devices

In low molar mass organosiloxane liquid-crystal materials the siloxane moieties micro-separate and aggregate in planes that could be regarded as an effective or virtual two-dimensional polymer backbone. We show that if a siloxane moiety is attached to a dichroic dye molecule, the micro-segregation of the siloxane moieties makes it possible to include a high concentration of the guest dye (more than 50%) in a host organosiloxane solution. This effect, combined with the temperature independent tilt angles achievable with ferroelectric organosiloxane liquid crystals, provide an ideal material for high-contrast surface-stabilised ferroelectric display devices. We present dyed ferroelectric materials with a temperature independent tilt angle greater than 42 degrees, a wide (room temperature to over 100°C) mesomorphic temperature range and a response time shorter than 500μs in the dye guest host mode.

Photoisomerising effects in nitroazo flexoelectric dimeric nematic systems

The photoisomerisation of a flexoelectric chiral nematic bimesogen system dyed with an azo dye has been investigated. The host material has a pitch and field dependent tilt angle that are temperature independent. Upon illumination by ultra violet, the azo dye molecules undergo a shape change from their trans to cis isomer. The effect of the shape change of the dye on the mixture is to decrease the I-N* transition temperatures, to increase the response times and to decrease the transmitted optical intensity. For the same reduced temperatures, the tilt angles, pitch and threshold voltages for the transition from focal conic to homeotropic textures are unchanged. The macroscopic parameters observed suggest that the orientational order parameter of the system is reduced by UV illumination. The cis isomers do not appear to separate from the host material or significantly change the flexoelectric coefficient. © 2001 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint, a member of the Taylor & Francis Group.

Low molar mass organosiloxane liquid crystals for telecommunication applications

Mixtures of two proprietary low molar mass organosiloxane liquid crystals were studied in order to improve their alignment and optimize their electro-optic properties for telecommunication applications. Over a certain concentration range, mixtures exhibited an isotropic-chiral smectic A-chiral smectic C (Iso-SmA*-SmC*) phase sequence leading to exceptionally good alignment. At room temperature, the spontaneous polarization of these samples was reduced from 225 nC cm -2 in the pure SmC* liquid crystal to as low as 75 nC cm -2 in the mixture. Within this concentration range, the ferroelectric tilt angle could be varied between 35° and 15°, while the rise time decreased by 69.4%. The rise times were < 45 μs for moderate electric fields of ± 10 V μm -1 in the SmC* phase and ∼ 4 μs, independent of electric field, in the SmA* phase. At λ = 1550 nm, these mixtures exhibited very large extinction ratios of {\sim} 60 dB for binary switching in the SmC* phase and ∼ 55 dB continuous variable attenuation in the SmA* phase. © 2012 IEEE.