Observation of Pretransitional Divergence of Shear Viscosity near a Smectic-A—Smectic-BPhase Transition

Strong pretransitional divergence of shear viscosity was observed for the first time near a smectic-A---smectic-B phase transition by capillary shear flow with the layer normal perpendicular to both the flow velocity and velocity gradient. The results are inconsistent with a single power-law type of critical exponent and are suggestive of an essential singularity. Possible implications of the results for recently proposed models of the smectic-B phase and mechanisms for smectic-A---smectic-B phase transitions are discussed.