High Pressure Dielectric Studies of a Substance with the Smectic A1 Phase
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چکیده
The results of dielectric studies of 5-n-hexyl-2-(4'-isothiocyanato)-l,3-dioxane (6DBT) in the smectic A, phase at pressures up to 150 MPa and temperatures up to 340 K are presented. The low frequency relaxation time T\\ (/?, T) yields the activation volume AV|| = RT(d ln Tjj/9/>)rand activation enthalpy A//jj = R(d ln T | | / 3 7 ) p . The calculated values of these parameters are compared with those obtained recently for n-octyl-cyanobiphenyl (8CB) forming the smectic Ad phase. In the case of 6DBT both these quantities are practically constant, whereas those for 8CB decrease, when going away from the phase transitions isotropic smectic A] (6DBT) or nematic smectic Ad (8CB). These differences support our earlier conclusion that increase of pressure leads to a breaking of the antiparallel associations of cyanobiphenyl molecules in the smectic as well as in the nematic phases.
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Study of High Frequency Relaxation Processes in Three Substances with the -CN Groups at the Lateral Positions
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