摘要:

The soft mode dielectric response of three ferroelectric chiral smectic C* substances is studied in the vicinity of the smectic C*-smectic A* phase transition. For some substances the soft mode dielectric strength exhibits a pronounced anomaly in the C* phase just below the phase transition. We show how this anomaly can be systematically correlated with a corresponding anomaly in the experimentally determined ratio of spontaneous polarization over tilt. By comparing the experimental results with the theoretical predictions of an extended Landau model, we demonstrate how the crossover behaviour of the system can be interpreted as being the consequence of the presence of a biquadratic coupling between tilt and polarization in the Landau free-energy of the system.

ISSN:0267-8292    

DOI:10.1080/02678299408029155

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

By means of high pressure differential thermal analysis we measured the pressure/temperature phase diagrams of several nematic compounds with different molecular structures. Using pressures up to about 500 M Pa we found strongly nonlinear clearing curves. This behaviour is interpreted as changes from ‘weak’ intermolecular potentials to ‘hard’ potentials, or using thermodynarmic arguments, strong pressure dependence of the volume discontinuity at the clearing transitions.

ISSN:0267-8292    

DOI:10.1080/02678299408029156

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nine members of the octa-n-alkanoyloxy-9,10-anthraquinone series, ranging from octanoyloxy (n= 8) to hexadecanoyloxy (n= 16) (wherenis the number of carbon atoms per chain), were prepared and their mesomorphic properties studied by differential scanning calorimetry and optical microscopy. All the compounds studied are mesomorphic with the higher homologues exhibiting two (forn≧ 12) or even three (forn≧ 14) columnar mesophases. Forn= 8 to 11, the phase sequence is C-DB-I, where DBis an optically biaxial mesophase with a two-dimensional pgg symmetry. Forn= 12, 13, the phase sequence is C-M3-DB-I, where M3is a highly ordered phase whose structure has not been identified. Finally forn= 14 to 16, the phase sequence is C-M3-DB-DA-I, where DAis an hexagonal phase. In all cases, the phases change from high to low order with increasing temperature and all transitions are first order. Compared with the corresponding hexa-substituted naphthoquinones the present series generates larger mesomorphic ranges and the higher homologues exhibit a uniaxial phase which is lacking in the hexa-substituted series. The increase in volume occupied by the aliphatic chains in the octa-substituted series is evidently sufficient to reduce the interaction between the aromatic cores of the different columns to permit the stability of a uniaxial phase.

ISSN:0267-8292    

DOI:10.1080/02678299408029157

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The transmission electron microscope technique enables direct visualization of disclination core structure of main chain liquid crystalline polymers. Generally, the lamellar structure, that is a function of type of polymer and molecular length, and of which the thickness is 10–200 nm, can be observed. In terms of distortions in the director field produced by a disclination, the elastic anisotropy, ε, can easily be calculated. However, the ε does not indicate the molecular distortion produced by the disclination. Continuum mechanics is used to describe the relationship between the elastic anisotropy, εa, measured from the lamellar director and that, εb, of the molecular director in main chain liquid crystalline polymers. The relationship is εa= −εb, indicating that lamellar distortion is completely different from the molecular distortion.

ISSN:0267-8292    

DOI:10.1080/02678299408029158

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0267-8292    

DOI:10.1080/02678299408029159

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0267-8292    

DOI:10.1080/02678299408029144

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor