Nature of layer-by-layer freezing in free-standing 40.8 films

Electron diffraction has been conducted in thin free-standing films of N-(4-n-butoxybenzylidene)-4-n-octylaniline (4O.8). The surface smectic-A layers first exhibit a transition to the hexatic-B phase at a temperature where a strong heat-capacity anomaly has been observed, and then undergo a second transition to the crystal-B phase. The surface hexatic-B-crystal-B transition is not accompanied by any detectable thermal signature, but coincides with the onset of shear response. This smectic-A-hexatic-B-crystal-B transition sequence is then repeated in the interior of the films in a novel layer-by-layer manner.