Abstract
Orientational order parameters (OOP's) have been determined in the Smectic A, Smectic C1 and Smectic C2 phases of a hockey stick-shaped compound from X-ray diffraction measurements and compared with NMR measurements. While the OOP values from NMR measurements abruptly drop at the Smectic C1 to Smectic C2 transition, those determined from X-ray diffraction measurements decreases sharply at the Smectic A to Smectic C1 transition. This drop in the OOP values from X-ray measurements has been explained using a model where the molecular director is randomly oriented in a cone about the smectic layer normal. OOP's from X-ray diffraction and NMR measurements have been successfully fitted with McMillan's theory, after necessary correction to the potential, incorporating tilt angles, for three homologues with n = 10, 11 and 12. The temperature dependences of the optical birefringence, dielectric anisotropy and OOP values determined from birefringence measurements of compound 11 are also reported.
Acknowledgements
Financial support from Department of Science and Technology, New Delhi (Project No: SR/S2/CMP-20/2005) to MKD and financial support from Department of Science and Technology, New Delhi (Project No: SR/S2/CMP-29/2007) to BD are gratefully acknowledged. The authors would like to thank the referees for their valuable comments and suggestions to improve the manuscript.