摘要:

Pyramidic mesogens forming thermotropic liquid crystal bulk phases were spread in an air-water interface. Pressure surface measurements and polarizing microscopy on the Langmuir films were used to characterize the various states of these pyramidic-like molecules. For two compounds bearing short lateral aliphatic chains, the surface pressure isotherms exhibit a large plateau region corresponding to a metastable monolayer in which the molecules may adopt an ‘edge-on’ arrangement. The coexistence of multilayered, anisotropic, slowly growing domains with the monolayer in the plateau region has been observed at long time scale. The film area relaxation kinetics at constant surface pressure show the existence of two nucleation mechanisms for the formation of these domains.

ISSN:0267-8292    

DOI:10.1080/02678299308027699

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The structure of Langmuir-Blodgett (LB) diacetylene films CH3‒(CH2)11‒C≡C‒C≡C‒(CH2)8‒COOCd1/2(DA1) and CH3‒(CH2)20‒CO2‒CH2‒C≡C‒C≡CH2OH (DA2) was studied by X-ray small angle scattering and electron diffraction methods prior to and upon their polymerization. It has been established that Langmuir films have layer packing. The periods of the constituent layers were determined as 58 Å (for DA1) and 69 Å (for DA2). This indicates the existence of a vertical bilayered packing of molecules. It has also been established that polymerization of LB diacetylene films due to the action of UV irradiation does not change the layer thickness appreciably and the structural rearrangement reduces to a slight redistribution of the electron density along the molecules which is explained by a break of the triple bonds during the UV irradiation.

ISSN:0267-8292    

DOI:10.1080/02678299308027700

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The homogeneous alignment of a liquid crystal material, 4′-n-octyl-4-cyanobiphenyl (8CB), was achieved by polyimide Langmuir-Blodgett (LB) films. Scanning electron microscopy and scanning tunnelling microscopy measurements show that the alignment of the polyimide LB films with a grooveless surface occurs due to the orientation of the polyimide chains. We directly observe 8CB monolayers on oriented polyimide LB films. We find that the monolayers form a two dimensional crystalline structure and the 8CB molecules are always aligned along the chain direction of the polyimide. The results show that the alignment of 8CB molecules arises by an epitaxial growth on the oriented polyimide LB films.

ISSN:0267-8292    

DOI:10.1080/02678299308027701

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Langmuir-Blodgett films of a discotic mesogenic pyrylium tetrafluoroborate salt (1) have been investigated from the point of view of their in-plane anisotropy, i.e. considering the average molecular orientation with respect to the dipping direction. The molecules are found to stand on edge with their flat polycyclic core more or less perpendicular to the dipping direction. Mixing1with N(C4H9)4+TCNQ−in the spreading solvent leads to a different behaviour of the monolayer at the air-water interface, involving the formation of the Pyrylium-TCNQ salt. In contrast to the films of pure1, these films do not exhibit any in-plane anisotropy after deposition on a solid substrate. The temperature dependance of the molecular anisotropy of both films has also been investigated. The results are presented and discussed in the framework of their mesomorphic properties together with the influence of the anion associated with Pyrylium.

ISSN:0267-8292    

DOI:10.1080/02678299308027702

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A mean field theory for cholesteric polymers based on the elastic model is presented. The effect of flexibility and the biaxial order and nematic order parameters are studied. The biaxial order and nematic order parameters are increasing functions of chirality and vary slightly with flexibility. Biaxiality is shown to be important for the transition temperature and the cholesteric pitch as well as the latent heat of transition.

ISSN:0267-8292    

DOI:10.1080/02678299308027703

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The synthesis of side chain-type polyurethanes is described. Their thermal properties were investigated by differential scanning calorimetry and polarizing microscopy and are discussed in terms of the dependence of the polymer backbone on temperature as shown by FT-infrared spectroscopy. The hydrogen bonding which arises from the rather flexible polymer backbone plays a more important role in determining the thermal stability than does the rigid polymer backbone.

ISSN:0267-8292    

DOI:10.1080/02678299308027704

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effect of thermal treatment on the thermodynamic properties and structure of a nematic thermotropic main chain polymer with mesogenic groups containing 3,3′-biphenylene units and octamethylene flexible spacers (BF8) has been studied by DSC and X-ray scattering. We have found that BF8 samples do not crystallize even on very slow cooling from the isotropic state, and possessed a glassy nematic structure at room temperature. The strong influence of the cooling rate on both the enthalpy of the nematic-isotropic transition and the rise of specific heat at the glass transition for BF8 samples was observed. It was attempted to explain this result in terms of the improvement of the nematic structure during cooling.

ISSN:0267-8292    

DOI:10.1080/02678299308027705

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Several series of liquid crystalline polyaroyl-bis-oxyarylates containing 1,4-phenylene, 4,4′-biphenylene and 2,6-naphthylene units have been synthesized with the use of aroyl-bis-oxyaroyl dichlorides. Melting and clearing temperatures of every polymer under investigation were compared with those of corresponding polyterephthaloyl-bis-4-oxybenzoates.

ISSN:0267-8292    

DOI:10.1080/02678299308027706

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Structural studies of a series of laterally attached side chain liquid crystalline polysiloxanes have been made by X-ray diffraction. All but one exhibit a nematic phase with SC-like short range ordering. The diffraction has been interpreted in terms of a model in which the mesogenic units form a ‘jacket’ around the polymer backbone. The backbone conformation has been studied by small angle X-ray scattering from oriented samples of mesomorphic solutions and by infrared dichroism measurements on oriented samples of the polymers. In both cases the results were consistent with the mesogens being oriented parallel to the backbone which is consistent with the ‘mesogen jacket’ model.

ISSN:0267-8292    

DOI:10.1080/02678299308027707

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We have measured the angular distribution of light scattered from PDLC films with micron-sized droplets as a function of film thickness and applied voltage. We find that a single scattering picture does not give a good description of the observed scattered intensity. In particular, the intensity falls off much more weakly with scattering angle than one would predict from the anomalous diffraction cross-section calculated by Zumer. We present a simple model for describing double and higher order scattering events that gives a better quantitative description of the experimental observations. The model can be combined with a model for the switching behaviour of PDLC films to describe the scattering as a function of the applied voltage.

ISSN:0267-8292    

DOI:10.1080/02678299308027708

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor