Static and viscoelastic properties of the various smectic phases of N-(4-n-pentyloxybenzylidene)-4-n-hexylaniline (50.6) determined by dilatometry and acoustic methods

摘要

High resolution dilatometric measurements of the various smectic phase transitions of N-(4-n-pentyloxybenzylidene)-4-n-hexylaniline (50.6) are reported. It is found that the N-A, C-B, B-F and F-G transitions are first-order while the A-C transition is second-order. Hysteresis effects at the B-F and F-G transitions are observed and seem to show that dislocations and defects play a significant rôle at these transitions. Calorimetry measurements show the existence of a new phase between the B phase and the F phase. The dynamic behaviour of the various smectic phases has also been investigated in presence of a shear which is parallel to the layers. The results demonstrate that all the smectic phases have a viscoelastic behaviour. It is shown that a coupling between long-range orientation order (the director) and the shear stress is one of the mechanisms contributing to the viscoelasticity of these phases. Comparison between the data obtained in phases C and F suggests that the director is coupled to the local lattice of the latter. The behaviour of the crystalline-B phase is identical to that observed previously in the crystalline-B phase of N-(4-n-butyloxybenzylidene)-4'-n-octylaniline (40.8).