Anticlinic-synclinic transitions in superthin free-standing smectic films

Anticlinic-synclinic transition was studied in superthin smectic films using polarized light reflected microscopy. The measurements were made in a compound exhibiting the Sm$C_{FI1}^*$ subphase in a narrow temperature interval between antiferroelectric Sm$C_A^*$ and ferroelectric Sm$C^*$ phases. In films we observed series of transitions which numbers increases with increasing film thickness. Surface ordering leads to increasing transition temperatures with decreasing film thickness and to change of orientation of the molecular tilt plane in layers. Succession of transitions results from the competition between the surface and the bulk ordering. We found that line string defects may form in film, their orientation and collective behavior result from elastic deformation of molecular ordering.