for the degree of Doctor of Philosophy in the Faculty of Scieace

EXPERIMENTAL STUDIES O N LIQUID CRYSTALLINE P H A S E S

A N D PHASE TRANSITIONS

A thesis submitted to the Bangal ore Ui~i versi ty

for the degree of Doctor of Philosophy in the Faculty of Scieace

by

GEETHA

G .

NAIR

Licpitl Chy,st;a.ls Labom tory Ritillili~ ROSC;IL'C~ Institute

Bangalo1.e 560080, INDIA

Deceinber 1992

DECLARATION

I hereby declare tliat the entire work enibodied in this thesis is the result of the inves tigalions carried out by me indepelideiitly in the Liquid Crystal Lab~rat~ory, Raiiian Research Institute, Bangalore, and that no part of it has bee11 s~ibniitted for the award of ally Degree, Diylonia, Associateship, Fellowship or ally other siiiiilar title.

GEETHA G. NAIR

"CERTIFIED"

Professor N .V.MADHUSUDANA Head, Liquid Crystal Laboratory

R a ~ i i a ~ i Research 111s tit ute BANGALORE 560080

CERTIFICATE

We certify that tliis tliesis lias beell coliiposecl by Ms. Geetlla G. Nair based on tlie illves tigatiolis carried out by lier a t tlie Liquid Crystal Laboratory, Raman Researcli Institute, Bangalore, under our supervision. Tlle subject matter of this tliesis lias not previously formed tlie basis of tlie award of any Degree, Diploma, Associatesliip, Fellowsliip or otlier similar title.

Professor S. CHANDRASEKHAR Liquid Crystal Laboratory Raman Research Institute BANGALORE 560080

Dr. R. CHANDRAMANI ^.C Department of Physics

Bailgalore University BANGALORE 560056

Acknowledgements

I express 1 1 1 ~ ~ deep sense o f gratitude to Professor S . Cl~andrasekhar for his stimulating guidance and constant encourageinent. I a m grateful t o him for

providing m e this opportunity t o work with him and his group.

I ail1 dccl>lvv iutlcbtctl t o Prof. R . Shashicihar for his g~lidauce ailcl llelp, especialluv during tile initial part o f this project. I thank him for introducing m e t o i l ~ e field o f licprid crystals.

I ail1 estrenlely g a t eful to Dr. S , Iirisllna Prasad for his help with my exper- inients. I3u t for llis t inlely grridance and friendivy advice, this work would never have been coml,leted.

h l y tllanks are title to Dr. B. R . Ratna for her help and t o Dr. V . N . Raja for nlauy usefrll discussions.

I thank Dr. R . Clhandramani, Department o f Phyvsics, Bangalore University, for her guidance and keen interest in illy 11r01.k.

I espi'ess illy sincere thanks to Prof. N . V. Madhusudana for t h e interest h e has s h o ~ t ~ n in tile progress o f nly work.

A4y thanks are also due to Prof. G . Heppke and Dr. C ~ I . Bahr, Gerinanyv, for ~ x o ~ ' i t l i n g tile co1nl)oilnds studied cstensively i n this tllesis and also t o Prof. llf. E. Ncubcrt, U S A , P i v f . J . fir. G o o d l ~ ~ y U.Ii., Dr. 13. I<. Sadashiva and Adr. B. Sl~ivakrrn~ar for giving s o n ~ e o f the materials.

I an1 tliailkfulto Ah. V. Nagaraj, Mr. A. hlani, Mr. H. S u b r a m ~ n ~ v a m , Mr. I<. Subminanya, A h . Ad. Ishacl, Mr. Dhason and A h . Majid for their tech- nical assistance; lo Mr. C. R. Ranlachandra Rao and Mr. R a j u Verghese for their help in obl aining good pllo t o g a p l ~ s and for designiilg the cover o f the the- sis; t o Dr. A . Ratnakar and t l ~ c lil~rary s t a f f ' for their valuable support and t o Mr. S . Rag-l~avachar for his kind help i n official matters.

Ad-v colleagues i'vli.. D. S. Shailkar Rao and Mr. S. h1. I<heued have helped m e a lot at 17ario11s stages o f illy work. I tllank t h e m botll ~vlloleheartedl~v. I ~vould like t o thank Als. I<. Usha for her illost e n j ~ ~ v a b l e coinpanvv througl~out, and all mvv friends and colleagrzes at R.R.I., for being nice t o me in ever-v .cvavv.

I thank m y parents, illy sister, n l y bi.otller and illy husband rvl~o have al\vavvs bee11 a constant source o f enconi.agement drrring tile course o f niy work.

Mv

very special t llai~ks are due t o niyv f i t her, brr t for ~vllose loving support I never ~vould have been able t o complete tdis project, and t o illy husband, hlr. G. Raju, for his cooperation and irnde~st anding dlrriiig the period o f this work. I also thank 111y i n - l a w wllo relicred n w o f 1111zcl1 o f illy clonicstic- responsibilities, ~ v l l i c l ~ 111ade it possible for 111e to yu~.~sue 111y st izdies.

Contents

Chapter 1 Illtroduc ti011

Chapter 2 First order A-C* /A-C transition

Chapter 3 Mean-field to tlricritical cross-over behaviour near the A-C* T C P

Chapter 4 Polarisat ion- tilt coupling and thermal variation of pitch in the C* phase

Cllap t er 5 Phase diagram involving the TGB phase

in the vicinity of

a

virtual Ch-A-C* point 85

Cllap t er

6

High pressure studies on some liquid crystals exhil~iting llexatic Bfcrystal B pliases

Cover Picture:

Fan shaped texture of smectic A liquid crystal as seen under a polarising microscope.