摘要:

A number of binary systems comprising a liquid crystalline Schiff's base, viz.p-acetoxybenzal-p-phenetidine and a non-liquid crystalline Schiff's base are studied. In all these cases, the liquid phase, be it anisotropic or not, is a single homogeneous phase. There is no indication of two distinct liquid phases, one anisotropic and the other isotropic, coexisting side by side over a range of temperature, for a binary system of a given composition.

ISSN:0369-1152    

DOI:10.1080/15421406608083065

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

Previously published data concerning ultrasonic absorption and dispersion at phase transitions in liquid crystals are reviewed. Extensions of the quantitative interpretation of such data are proposed. The similarities between the ultrasonic behavior of liquid crystalline compounds near the isotropic-nematic transition and that of simpler compounds in the critical region leads to the application of Fixman's (1965) expressions to the data forp-azoxyanisole. Fixman's theory provides as satisfactory a fit to experimental data at temperatures just above the transition point,Te'as Frenkel's heterogeneous fluctuation theory (1955). Furthermore, it has the advantage of treating a specific mechanism of absorption, namely, the temperature-dependent oscillation of the spatial decay constant,kin the approximation of Ornstein and Zernicke to the radial distribution function. A value of Debye's short range ordering parameter,l, equal to 11.2 Å is found forp-azoxyanisole andTc. In the nematic state (T Te) Maier and Saupe's (1960) theory appears to be inadequate to account for the measured ultrasonic absorption. This conclusion is tentative. A combination of Maier and Saupe's expressions and Fixman's expressions withl+8.1 Å can bring about agreement with the experimental data of Hoyer and Nolle (1958) just below the transition point. In this case Fixman's expressions are considered to be applicable to transition regions between adjacent domains having different orientations of the local optic axis.

ISSN:0369-1152    

DOI:10.1080/15421406608083066

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

Effects of strong electric fields upon cholesteric liquid crystals have been studied. Increased intensity of light selectively scattered from the plane texture at d.c. and up to 3 kc have been found, as well as a temperature-dependent minimum in the average intensity as a function of frequency. An effect somewhat like hysteresis is shown by retention of the acquired brightness in the absence of field. Curious effects such as three classes of dark spots, some of which metamorphose into bars, light maltese crosses, and bright cross-hatchings are regularly observed.

ISSN:0369-1152    

DOI:10.1080/15421406608083067

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

摘要:

Chairman:As a result of opinions obtained through prior discussion with a cross-section of participants at the conference, the meeting was asked to consider the advisability of standardizing nomenclature and symbols relating to liquid crystals, particularly with regard to achiving an unambiguous means of recording the number of crystalline and liquid crystalline states exhibited by a compound and the temperatures at which transitions between these states occurred.

ISSN:0369-1152    

DOI:10.1080/15421406608083068

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor

ISSN:0369-1152    

DOI:10.1080/15421406608083069

出版商:Taylor & Francis Group    

年代:1966

数据来源: Taylor