摘要:

This article describes the state of and progress in experimental studies of liquid crystals of naturally occurring nucleic acids and synthetic polynucleotides. The areas considered in this review include: (i) the liquid-crystalline phase of nucleic acids in aqueous salt solutions, (ii) the liquid-crystalline phase of nucleic acids in aqueous polymer solutions, (iii) the liquid-crystalline phase of nucleic acids in living systems. Some unsolved problems which are of interest from both a physicochemical and a biological point of view are discussed.

ISSN:0267-8292    

DOI:10.1080/02678298808086687

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

We report X-ray diffraction, density, ultrasonic velocity and refractive index studies in theN(p-n-pentyloxy benzylidene)p-n-alkylaniline compounds, viz. 50.5, 50.6 and 50.7. The nematic-smectic A (NA) transition is found to be weak first order in 50.6 while it is second order in 50.5 and 50.7. The salient features observed are cybotactic clusters in the nematic phase in all the compounds, molecular tilt which was inferred due to the end alkyl chains tilt causing orienta-tional disorder (smaller orientational order parameters ‘s’ than expected) in smectic A phase, smectic F phase and large tilt angle variation in smectic C phase in a small temperature range in 50.5. The observed results are discussed in the light of available data in othern0.mcompounds.

ISSN:0267-8292    

DOI:10.1080/02678298808086688

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A driven voltage-controlled reversible electrooptic effect in a smectic A phase with a preceding twisted nematic phase or a large-pitch cholesteric phase and SiO anchoring has been discovered. The unique feature of this novel electrooptic effect in a smectic A is that it reverses by relaxing when the electric field is removed. The conditions permitting the observation of such an effect are described in detail. On the basis of the smectic A textures observed a simple topological model is given. The influence of the polyvinyl alcohol anchoring is studied in the following paper. The main advantages and disadvantages of this novel electrooptic effect for a display device are briefly discussed.

ISSN:0267-8292    

DOI:10.1080/02678298808086689

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The driven voltage-controlled reversible electrooptic effect in a smectic A phase with a preceding nematic phase twisted by SiO anchoring, previously discovered (cf. the previous paper) has been studied with polyvinyl alcohol (PVA) anchoring. The unique feature of this novel electrooptic effect in smectic A phases is that it reverses by relaxing when the electric field is removed. For the case of PVA anchoring the reversibility of the effect only occurs near the smectic A-nematic phase transition in the smectic A phase. The temperature region of the reversibility of this effect can be widened with a higher voltage. A comparison with the case of a reversible electrooptic effect in a smectic A with a preceding twisted nematic phase and SiO anchoring is made. The possible application of this electrooptic effect in liquid crystal displays with storage is discussed briefly.

ISSN:0267-8292    

DOI:10.1080/02678298808086690

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The synthesis and liquid crystal properties of some bis(N-p-(n-alkoxy)phenyl,p-(n-alkoxy)salicylaldiminato)copper(II), of a homologous series of bis(N-p-(n-alkanoyloxy)phenyl,p-(n-alkanoyloxy)salicylaldiminato)copper(II), and of some corresponding palladium(II) complexes are reported. All of the compounds examined exhibit enantiotropic smectic mesomorphism, predominantly of the C type. Palladium(II) complexes are mesomorphic up to higher temperatures than the copper(II) homologues.

ISSN:0267-8292    

DOI:10.1080/02678298808086691

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Low molar mass analogues of liquid-crystalline polyesters were prepared in which two α-methylstilbene groups are joined through an alkyl spacer. Their mesogenic behaviour was investigated using differential scanning calorimetry, X-ray diffraction and optical microscopy. The experimental results show that the formation of smectic phases is favoured by increasing the length of the terminal chains and by decreasing the length of the flexible spacer. For a given flexible spacer, the melting point and the nematic-isotropic transition temperature are enhanced by decreasing the length of the terminal chains. The terminal chains seem to have no substantial effect on the large odd-even effect exhibited by the thermo-dynamic properties associated with the nematic-isotropic transition.

ISSN:0267-8292    

DOI:10.1080/02678298808086692

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The smectic I, F, J and G phases of the chiral ferroelectric compound (+)-(4-(2′-methylbutyl)phenyl 4′-n-octylbiphenyl-4-carboxylate) (+ 2M4P8BC) were studied by means of optical microscopy and X-ray diffraction. The free-standing film method was used. The films were additionally ordered with a d. c. electric field and true monodomain samples were prepared and examined.

ISSN:0267-8292    

DOI:10.1080/02678298808086693

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The electro-optical dynamics, hysteresis effects, and microscopic structure of polymer-dispersed films of nematic liquid crystal are probed in order to gain insight into the operation of this new class of liquid crystal light valves. In tracking the rise and decay response times of these devices, it appears that there are both ‘fast’ (0·1·l.0ms) and ‘slow’ (10-1000ms) processes that occur in the film. A model is proposed which explains these results, in which the reorientation of the nematic droplets takes place in two stages: a fast reorientation by the nematic within the bulk of the droplet, followed by a slower rotation of the nematic nearer the droplet surface (including the point disclinations). This model agrees with a similar proposal made by Doaneet alin a previous study of related films. This model is also used to explain both the behaviour of the films in response to short voltage pulses and hysteresis effects present in the film. The response time of these films can be tailored by adjusting the droplet size within the film, as well as the choice of the drive waveform and voltage. The non-spherical shape of the nematic droplets in the film is proposed to be the most important factor controlling the electro-optic properties of these devices. Data is presented which shows that the more distorted the nematic cavity, the more quickly the film decays, and the higher the field required for reorientation. It is proposed that the minimization of deformation energy of the nematic in a non-sperical cavity is the primary driving force for relaxation in these films, rather than previously postulated ‘surface interactions’

ISSN:0267-8292    

DOI:10.1080/02678298808086694

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The kinetics of band formation has been followed during the relaxation of anisotropic solutions of poly(n-hexylisocyanate) in toluene previously subjected to a shear rate, for a time ts. There is a threshold at low, or ts, below which bands do not appear (formation timetb→ ∞). Past the threshold,tsdecreases with either orts, and eventually bands are seen immediately after stopping the flow (tb= 0). However, for still larger particularly for the more viscous solutions and when the flowing solution is well oriented, tbmay increase again. The results are similar to those already reported for hydroxypropylcellulose in water and support a previous suggestion for the origin of the banded texture.

ISSN:0267-8292    

DOI:10.1080/02678298808086695

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A variety of homologous 1-deoxy-1-(N-methylalkamido)-D-glucitols were prepared and their liquid crystal phases characterized. In this study the thermotropic liquid-crystalline properties of these materials are investigated. The mesophases formed are shown to be of the smectic A class with an interdigitated bilayer ordering of the constituent molecules. This ordering is thought to be stabilized by hydrogen-bonding between neighbouring carbohydrate moieties. The properties of these materials are compared with those of other closely related acyclic carbohydrates.

ISSN:0267-8292    

DOI:10.1080/02678298808086696

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor