J. Phys. II France
Volume 7, Numéro 11, November 1997
Page(s) 1693 - 1707
DOI: 10.1051/jp2:1997210
J. Phys. II France 7 (1997) 1693-1707

Effect of a Strong Electric Field on the Reentrant Nematic to Smectic A $_{\rm d}$ Phase Transition

Geetha Basappa1, A.S. Covind1, 2 and N.V. Madhusudana1

1  Raman Research Institute, C.V Raman Avenue, Bangalore 560 080, India
2  Department of Physics, Vijaya College, Basavanagudi, Bangalore 560 004, India

(Received 27 February 1997, revised 20 May 1997, accepted 3 July 1997)

We report experimental studies on the effect of a strong electric field on the nematic-smectic A $_{\rm d}$ (N-A $_{\rm d}$) and A $_{\rm d}$-reentrant nematic (A $_{\rm d}$-N $_{\rm R}$) phase transitions in a binary mixture. Both the transition temperatures increase with field. The A $_{\rm d}$-N $_{\rm R}$ transition point changes much more rapidly than that of A $_{\rm d}$-N transition, indicating that the A $_{\rm d}$ phase will get bounded at a sufficiently high field. We have included the effect of the electric field in our molecular model of reentrant phases in highly polar compounds, in which the mutual orientation of near neighbour molecules changes from an antiparallel to a parallel configuration as the temperature is lowered. It is argued that the cross-over temperature increases with field which accounts for the observed trends. For suitable parameters, it is also predicted that either a nematic-nematic transition line can branch off from the A $_{\rm d}$-N $_{\rm R}$ line or a smectic A-smectic A transition line can meet the A $_{\rm d}$-N $_{\rm R}$ line at an appropriate field. In the latter case, the A $_{\rm d}$-N $_{\rm R}$ line has an associated slope change which is consistent with the experimental data.

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