Step-by-step thinning of free-standing films above the smectic-A–nematic phase transition

Optical reflectivity of free-standing films at the smectic-A–nematic (Sm-A–N) phase transition has been studied. The Sm-A films thin in a stepwise manner in the nematic temperature interval. The film thickness can be described by a power function of maximal temperature at which this thickness is stable. The value of the exponent correlates with ${\nu }_{\mathrm{\parallel }}$ for the smectic fluctuations in the nematic phase determined by x-ray diffraction. The step-by-step thinning is a universal phenomenon for the smectic-A–nematic phase transition.