Mechanical Measurements of the Smectic-B−ATransition in Liquid-Crystal Films

A low-frequency torsional oscillator has been used to measure the temperature dependence of the in-plane shear modulus and dissipation of freely suspended films of butyloxybenzylidene octylaniline. It has been observed that smectic-$B$ films have a solidlike shear modulus and that the smectic-$B-A$ transition proceeds in at least two separate steps. The lower-temperature transition is the bulk melting while the higher-temperature transition is tentatively identified as surface melting.