Isabelle Kraus

Thèse soutenue le 13 janvier 1995

Etude des films librement souspendus de cristaux liquides thermotropes en phase smectique

Can one hear the structure of Smectic Films ?

During her thesis work, Isabelle Kraus has shown that the frequency and the quality factor of eigenmodes of a smectic drum are sensitive to several parameters such as : 1°- the tension of the film, 2°- its thickness h=Nd, 3°- its structure (SmA, SmB, SmI, ...). As an example, we show below the spectra of the same eigenmode (2,1) recorded at the same temperature with two 7O.7 rectangular films having the same lateral dimensions but different thicknesses.

When smectic films are drawn on frames which are not flat, like on the example shown below, they acquire a built-in gaussian curvature. Vibrations of such curved films necesserily involve changes in their metric. As a result, when smectic layers have an in-plane elasticity, the induced elastic stresses contribute to the restoring force and shift up the frequency of modes.

For a given gaussian curvature of the film - (1/R_o)², the frequency shift is proportional to the in-plane elasticity of smectic layers. For example in the case of a 7O.7 film of thickness h = 12400 Å, the shift of the tune of the (1,2) mode at 62 °C is of about 30%. It corresponds to the SmA -> SmB transition. Therefore, this phase transition is audible.

I. Kraus, P.Pieranski, E. Demikhov, H. Stegemeyer and J. Goodby.

"Destruction of a first-order smectic-A→ smectic-C* phase transition by dimensional crossover in free-standing films."

Physical Review E 48, no. 3 (1993): 1916

I. Kraus, P. Pieranski, E. Demikhov, H. Stegemeyer, J. Goodby, A. Slaney, and M. Osipov.

"Surface Ordering and Finite‐size Effects at the First Order Phase Transition SmA‐SmC in Liquid‐crystalline Free‐standing Films."

Berichte der Bunsengesellschaft für physikalische Chemie 97, no. 10 (1993): 1376-1380.

I. Kraus, P. Pieranski, and E. Demikhov.

"Phase transitions induced by a change in the tension of freely suspended smectic films."

Journal of Physics: Condensed Matter 6, no. 23A (1994): A415.

I. Kraus, C.Bahr and Pawel Pieranski.

"Mechanical perturbation applied on freely suspended smectic films."

Molecular Crystals and Liquid Crystals 262, no. 1 (1995): 1-12.

I. Kraus, C. Bahr and Pawel Pieranski.

"Mechanical properties of freely suspended smectic films."

Journal de Physique II 7, no. 11 (1997): 1617-1634.

Ch. Bahr, I. Kraus, J.V. Chikina and P. Pieranski

„Can one hear the structure of smectic films”

Phys. Rev. E. 58 (1998) 610

Page updated

Google Sites

Report abuse