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Abstrakty
The absorption and velocity of ultrasonic longitudinal waves in the nematic liquid crystal 1-(trans-4-hexylcyclohexyl)-4-isothiocyanatobenzene (6CHBT) have been measured as a function of temperature between 24°C and 55°C at 5.2 MHz. The temperature dependence of ultrasonic absorption has a sharp maximum, whereas that dependence of velocity shows a local minimum in the region of the nematic-isotropic (N-I) phase transition. Additional temperature measurements of density have been done to calculate the thermal coefficient of expansion and the temperature coefficient of adiabatic compressibility. Both these parameters exhibit critical behaviour at the transition which has been analysed. The values of the exponent determining the growth of the order fluctuations have been calculated and compared with references.
Wydawca
Czasopismo
Rocznik
Tom
Strony
373--378
Opis fizyczny
Bibliogr. 8 poz., tab., wykr.
Twórcy
autor
- Institute of Fundamental Technological Research, Polish Academy of Sciences, Świętokrzyska 21, 00-049 Warszawa, Poland, abalcerz@ippt.gov.pl
Bibliografia
- [1] DE GENNES P. G., PROST J., Physics of liquid crystals, Clarendon Press, Oxford 1998.
- [2] KAWAMURA Y., MAEDA Y., OKANO K., IWAYANAGI S., Anomalous ultrasonic absorption and dispersion of nematic liquid crystals near the clearing point, Jap. J. Appl. Phys., 12, 1510-1521 (1973).
- [3] SPERKACH Y. V., SPERKACH V. S., ALIOKHIN O., STRYBULEVYCH A. L., MASUKO M. , Temperature dependence of acoustical relaxation times involving the vicinity of N-I phase transition point in 5CB liquid crystal, Mol. Cryst. and Liq. Cryst., 366, 183-202 (2001).
- [4] NATALE G. G., The contribution of ultrasonic measurements to the study of liquid crystals. I. Nematics, J. Acoust. Soc. Am., 63, 1250-1278 (1978).
- [5] A. DRZYMAŁA, M. CIEŚLAK, D. WILK, Investigations of the thermotropic liquid crystals and epidian 3 by an application of acoustic methods [in Polish], Proceedings of XLVII Open Seminar on Acoustics, Rzeszów 2000.
- [6] GEORGE A. K., On critical phenomena in liquid crystals, Acustica, 73, 287-290 (1991).
- [7] E. P. PAPADAKIS, Ultrasonic phase velocity by the pulse-echo-overlap method incorporating diffraction phase corrections, J. Acoust. Soc. Am., 42, 1045-1051 (1967).
- [8] P. H. KEYES, J. R. SHANE, Tricritical exponents for the isotropic-nematic transition: an experimental verification, Phys. Rev. Lett., 42, 722-725 (1979).
Typ dokumentu
Bibliografia
Identyfikator YADDA
bwmeta1.element.baztech-article-BAT3-0025-0025