I. Kraus et al., DESTRUCTION OF A 1ST-ORDER SMECTIC-A -] SMECTIC-C-ASTERISK PHASE-TRANSITION BY DIMENSIONAL CROSSOVER IN FREESTANDING FILMS, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 48(3), 1993, pp. 1916-1923
Shifting and destruction of phase transitions due to the finite thickn
ess of free-standing smectic films are examined. The behavior of smect
ic films is studied as a function of the temperature and the thickness
in a material showing a first-order smectic-A (Sm-A)-->smectic-C (Sm
-C) bulk phase transition. Measurements of the optical reflectivity a
nd direct observations in an inverted polarizing microscope reveal tha
t the first-order phase transition between Sm-A- and Sm-C-like struct
ures takes place in films that are thick enough (N > N(c) = 90). In th
in films (N < N(c)) this transition disappears. For N almost-equal-to
N(c), a critical behavior is detected. A theoretical scheme for interp
retation of phase transitions in smectic films is proposed and on its
basis a conjecture on tension-induced phase transitions is formulated.