摘要:

The switching process in ferroelectric liquid crystal devices takes place through the formation and evolution of domains, which can be modelled using a three variable approach. Here we discuss details of the model which are necessary in order to reproduce the domain nucleation and switching times as a function of applied voltage for both monopolar and bipolar pulses. We show that in order to reproduce data correctly the model must incorporate a complex empirical elastic stress term.

ISSN:0267-8292    

DOI:10.1080/026782997208893

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Scanning tunnelling microscopy (STM) can be used to image adsorbed organic molecules in real space and real time. The technique seems especially well suited for imaging 2-D crystalline monolayers formed under liquid crystal films. In addition to observing perfect 2-D crystals, STM provides the ability to observe crystal defects, and to observe how these defects evolve over time. In this study two different vacancy defects in 2-D lamellar monolayers of chiral liquid crystal molecules under bulk smectic films were observed in situ. Both vacancies showed dynamic behaviour and an unexpected transport anisotropy.

ISSN:0267-8292    

DOI:10.1080/026782997208901

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The liquid crystalline systems studied consisted of non-chiral mesomorphic esters [the eutectic mixture of 4-n-hexyloxyphenyl 4-n-octyloxybenzoate and 4-n-octyloxyphenyl 4-n-hexyloxybenzoate] and structurally similar chiral dopants (N-arylidene derivatives of S-1-phenyl- and S- 1-benzyl-ethylamine). Twist grain boundary phases occur between the cholesteric and smectic C* or smectic A phases in all the investigated systems. The different structures of these TGB phases (TGBA and TGBC) are proved by small angle X-ray scattering and textural studies. The concentration and temperature ranges of the TGB phases are defined by the twisting power of the chiral dopants and their own mesomorphic peculiarities. The experimental dependences of TGB phase temperature range on cholesteric helical twist are influenced by a ratio change of the optically active and racemic forms of the dopant at a constant total concentration. The results obtained are discussed within Renn's theory.

ISSN:0267-8292    

DOI:10.1080/026782997208910

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The behaviour of the mesophase directors when a sample with a negative anisotropy Deltachi in the magnetic susceptibility is rotated at a speed omega in a magnetic field B0 about an axis inclined at an angle beta is investigated by deuterium NMR spectroscopy. There are combinations of beta and omega which lead to the directors aligning along the spinning axis (stable region), and other combinations where the directors are either unaffected by the rotation, or have a timedependent distribution (unstable region). These two regions are separated by a line (the q line) whose position depends on beta and omegac DeltachiB02/2mu0gamma1, where gamma1 is a twist viscosity coefficient. Experiments on 4-n-propyl-4-cyanobicyclohexane (CCH3) are used to demonstrate how the q line, and hence omegac may be determined. Combining this result with a measurement of the anisotropy in the magnetic susceptibility, Deltachi, yields a value for gamma1.

ISSN:0267-8292    

DOI:10.1080/026782997208929

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The strong prolate anisotropy of the backbone conformation observed in the nematic phase of ‘side-on fixed’ LCP is found to be as great as for main chain LCP. From this remark originated this SANS study of a ‘jacketed’ polymer PA4,4,4. A form factor of cylinders is used to model the experimental scattering data as in the case of main chain LCPs. The data are well fitted by this model and the backbone appears as a long and very thin rigid rod.

ISSN:0267-8292    

DOI:10.1080/026782997208938

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new series of ferroelectric liquid crystal materials containing a lateral methyl group on the aromatic ring of the alkoxybenzoate unit has been synthesized and investigated. These materials exhibit a wide temperature range of ferroelectric SmC* phase on cooling (including supercooling) with a very high spontaneous polarization. All phase transition temperatures are lower when compared with those of similar non-substituted materials. In comparison with the compounds containing the lateral methoxy group, only the SmC*-Cr transition changed significantly. The values of spontaneous polarization are mostly increased compared with both non-substituted and methoxy substituted compounds.

ISSN:0267-8292    

DOI:10.1080/026782997208947

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The three isomeric guanylic acids (5'-GMP, 3'-GMP and 2'-GMP) and the 3':5'-cyclic derivative (cGMP) form, in water solution, left-handed columnar aggregates which, at higher concentration, pack to give left-handed cholesteric mesophases. The self-assembly process and liquid crystal formation are discussed in relation to the behaviour of the 2'-deoxy analogues.

ISSN:0267-8292    

DOI:10.1080/026782997208956

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In previous work [1-4] we found, for the first time, that the selectively reflected light band from cholesteric liquid crystals depends on the physical sorption properties of their supports, and we now use them to differentiate nickel electrodeposits with different grained texture and NixOy with various thicknesses. The different nickel oxide thicknesses were prepared by dipping the nickel electrodeposit samples into H2O2 solution for different time intervals. The selectively reflected light measurements from using the above samples were compared to each other, as well as to those from samples not dipped in H2O2 solution. All the experimental results were correlated with the properties of the deposits, as well as with the results derived from SEM. It is concluded that cholesteric liquid crystals can provide an efficient technique to identify surfaces with different grained texture and thickness of formed oxide.

ISSN:0267-8292    

DOI:10.1080/026782997208965

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We study in detail the influence of deviations from the molecular cylindrical symmetry on the fundamental elastic properties of uniaxial nematic liquid crystals. Results for the elastic constants are obtained for a range of molecular length-width ratio, temperature, density and molecular parameters. We compare calculated values with the experimental data of 8 OCB. It is observed that the effect of non-cylindrical molecular symmetry on the values of elastic constants of uniaxial of a nematic phase is small.

ISSN:0267-8292    

DOI:10.1080/026782997208974

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A supramolecular mesophase was prepared from molecular recognition directed self- assembly of two complementary molecular components, namely 5-(4-dodecyloxy- benzylidene)-2,4,6-(1H,3H)-pyrimidinetrione and 4-amino-2,6-didodecylamino-1,3,5triazine. Differential scanning calorimetry measurements indicate a mesophase having liquid crystalline properties. Infrared studies suggest that not only hydrogen bonds but also pi-aromatic stacking and van der Waals interactions direct the formation of the mesophase.

ISSN:0267-8292    

DOI:10.1080/026782997208983

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor