CHINESE JOURNAL OF PHYSICS VOL. 38, NO. 3-I JUNE 2000

Several Anomalous Thermal Behaviors in Free-Standing
$\bmit N$-(4-$\bmit n$-butoxybenzylidene)-4-$\bmit n$-octylaniline Films

P. J. Wu¹, Y. C. Shen¹, Y. H. Liu¹, C. R. Lo¹, A. J. Jin²,

C. C. Huang², and C. Y. Chao<sup>1

1</sup>Department of Physics, National Central University,

Chung-Li, Taiwan 320, R.O.C.

²School of Physics and Astronomy, University of Minnesota,

Minneapolis, Minnesota 55454, USA
(Received November 24, 1999)

Entirely $\;$novel $\;$phenomena $\;$associated $\;$with $\;$the $\;$phase $\;$transitions $\;$of $\,N$-(4-n- butoxybenzylidene)-4-n-octylaniline (4O.8) free-standing liquid-crystal films are discovered. The hexatic-B ordering transition of the outermost surfaces has only a small thermal hysteresis and exhibits a predominant pretransitional heat-capacity anomaly, in disagreement with the predictions of two-dimensional melting theory. In light of our recently established results of the surface-enhanced two-stage freezing transformation [1], even a single interior layer shows a smectic-A-crystal-B transition and exhibits a drastic thermal hysteresis (about 10 $^\circ$C). The melting transitions are also unique in which, even though the interior crystal-B phase can unusually melt at a much higher temperature than the surfaces, the surface anomaly peaks occur in a layer-by-layer fashion with about the same sizes as in the cooling.

PACS. 64.70.Md - Transitions in liquid crystals.
PACS. 61.30.-v $\;\,$- Liquid crystals
PACS. 64.60.Kw - Multicritical points.

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