Twist-grain-boundary-A* phase stabilisation in confined geometry by the interfaces

ABSTRACT

We report on the appearance and stabilisation of twist-grain-boundary-A (TGB) phase in confined geometry samples of the liquid-crystalline compound CE8, by means of polarised optical microscopy. The chiral liquid crystal (LC) compound was chosen such as to undergo a cholesteric–smectic-A transition with temperature (type-I smectic), and to be close to the triple point between the cholesteric, TGB, and smectic-A phases. We used several types of anchoring conditions and various effective anchoring strengths. The results reveal that (i) the TGB phase exists as a metastable phase with strong fluctuations in the bulk, and (ii) it can be stabilised by the sample boundaries for adequate anchoring conditions. This means that we probably observed a type-I to type-II smectic transition induced by the substrate. Some dependence of the stabilisation on the surface-anchoring conditions and on the cell thickness is reported.

Graphical Abstract

KEYWORDS:

• Liquid crystals
• twist-grain-boundary phase
• anchoring conditions
• optical microscopy

Acknowledgements

M.T. acknowledges the support of the Project PR-05015 of the Slovenian Research Agency. G.C. and I.L. acknowledge the support of the Project PE3-1535 implemented within the framework of the Action ‘Supporting Postdoctoral Researchers’ of the Lifelong Learning, co-financed by the European Social Fund and the State of Greece. G.N. and I.L. acknowledge support and funding by the ARISTEIA Program No. 1125 administered by the General Secretariat for Research and Technology co-financed by the European Social Fund and the State of Greece. The authors would like to thank Janja Milivojević and Miha Škarabot for technical assistance related to the preparation of cells.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Greek Ministry of Education, action ‘Support of Postdoctoral Researchers’ [grant number PE3-1535]; the Greek General Secretariat for Research and Technology, action ‘ARISTEIA’ [grant number 1125]; the Slovenian Research Agency [grant number PR-050515].