We report a detailed study of the shear mechanical impedance near the crystalline-B-smectic-A transition in butyloxybenzylidene octylaniline (40.8). The measurements were performed at various frequencies from 5 to 85 MHz for shear waves propagating along the normal to the layers. In both phases the material response presents strong relaxation effects. The structure change at the transition is indicated by an increase in the real part of the shear impedance. The results at 85 MHz are those expected for a first-order transition broadened by impurity concentration, whereas the results at 5 MHz reveal a pretransitional effect in a temperature interval of 2-3 °C below the transition
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The behaviour of a smectic B phase (BBOA) has been investigated by means of shear wave reflectance techniques in the case of propagation parallel to the normal of the layers. No transmission of the shear wave has been observed. In addition, the experimental results in the A and B phases show a relaxational process, which leads to an apparent finite value for the shear modulus. Our results are discussed in the frame-work of the de Gennes-Sarma model and appear to support this model
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.Journal de Physique, 1984, 45 (2) solide-B présente un comportement identique à celui déjà observé dans la phase solide-B du N-(4-n-butyloxybenzylidène)-4'-n-octylaniline (40.8).Abstract. 2014 High resolution dilatometric measurements of the various smectic phase transitions of N-(4-npentyloxybenzylidene)-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).
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