Biomedical subjects

P Sonntag

Publications and source records attributed to P Sonntag.

7 recordsLinked to original sources

PubMed2000

Critical behavior of the de gennes elastic constants near the nematic-smectic- A transition of TBBA

We have studied the behavior of elastic constants A, B, and C deduced from ultrasound velocity anisotropies in the vicinity of the nematic-smectic- A transition of terephthal-bis- p- p(')-butylaniline. A is associated with compressibility, B with layer compression, and C with the coupling between compressibility and layer compression. We show that the exponent of A is of the preasymptotic 3D- XY type, whereas those of B and C are in between the 3D- XY values and those associated with the anisotropic fixed point. This behavior is consistent with the extended crossover regime predicted by Patton and Andereck [Phys. Rev. Lett. 69, 1556 (1992)].

Journal Article↗

PubMed2000

Dynamic scaling of ultrasonic damping near the nematic-smectic- A transition of TBBA

We report a detailed study of the ultrasonic damping near the nematic-smectic- A phase transition of terephtal-bis- p-p(')-butylaniline (TBBA). Two mechanisms contribute to the damping. One is isotropic; it is associated with the critical fluctuations, and leads to a scaling behavior of the 3D- XY type which is observed up to 15 degrees C from the transition, even though the transition is first order. The other is anisotropic; it appears only in the smectic- A phase, and is associated with the relaxation of the order-parameter modulus.

Journal Article↗

PubMed1997