抄録
Phase transitions of freely suspended chiral smectic films exhibiting a first order phase transition in a bulk system are studied in the framework of a phenomenological theory, in which such a widely observed finding that the surface layer orders at a temperature higher than the bulk critical temperature is taken into account. While the inner portion of the film exhibits the first order phase transition at a temperature below that of the surface layer in the system of sufficient thickness, a continuous change occurs for the system with a thickness smaller than a critical thickness. The mechanism of the continuous change is elucidated on the basis of the phase diagram of the bulk system on the field versus temperature plane, where nonuniformity due to the ordered surface layers is replaced by an effective field and the high-temperature phase is connected continuously to the low-temperature one by the insertion of an unstable state between them.
