ELECTRON-DIFFRACTION STUDIES OF PHASE-TRANSITIONS IN 4O.8 FREESTANDING THIN-FILMS

The structural phase transitions of free-standing thin films of N-(4-n -butyloxybenzylidene)-4-n-octylaniline (4O.8), which exhibits smectic- A and crystal-B phases in the bulk, have been studied in detail using electron diffraction. When a smectic-A film is cooled, the outermost l ayer transforms initially to the hexatic-B phase and subsequently to t he crystal-B phase at a lower temperature. The first transition is con sistent with the thermal anomaly in the heat capacity and the second t ransition coincides with the shear response observed in mechanical mea surements. Upon further cooling, the film undergoes additional layer-b y-layer smectic-A-hexatic-B-crystal-B transitions in its interior.