Multiple pathways to stabilize/induce an ordered phase in a system exhibiting a reentrant sequence

ABSTRACT

Liquid crystals have served as model materials for observing re-entrant phases, now known among a plethora of condensed matter systems spanning from superconductors to proteins. Sadashiva synthesised the organic compounds for the work from Raman Research Institute that laid the claim for having observed a re-entrant nematic in a single component material at atmospheric pressure. With no exception, the presence of such a re-entrant nematic necessitates the existence of an Intermediate smectic phase. After nearly half a century of this ground-breaking research, chemical and thermodynamic routes are well known for the relative stability of the smectic and re-entrant nematic. Here we describe some recent results and new research looking at other pathways to stabilise the smectic phase at the cost of the re-entrant structure. Specifically, we have employed additives such as carbon nanotubes, a non-aromatic polymer and photoisomerisation associated shape change of the molecules to achieve this target. A judicious combination of the nanophase segregation mechanism and the frustrated spin gas model can explain most of these observations. However, the phase diagram obtained in the temperature – intensity of actinic light phase spaces cannot be fully understood by these explanations, for which we have invoked other possible mechanisms.

Graphical Abstract

KEYWORDS:

• re-entrant phenomena
• CNT
• PMMA
• actinic light
• photoisomerization

Acknowledgements

It is a pleasure to be writing this article as a tribute to Professor B.K. Sadashiva (BKS). Two of the authors had personal interactions with him. One of us (DSSR), although did not have any formal collaboration, but knew him after joining RRI as a doctoral student and recalls interactions on various occasions discussing science as well as other matters. DSSR appreciates that despite the fact that Sadashiva was already a professor, he never kept the distance and always easily approachable. SKP is grateful to BKS for discussions on the reentrant systems, some of which were his initiation to research. He also fondly recalls extensive interactions with this tall cricketer-chemist during the visits to UK (2006) and Sapporo (2007); a more personal account of SKP’s reminiscences have already appeared in Liquid Crystals [58].

One of the authors (SKP) thanks Dr. Geetha Nair, a colleague at CeNS and Dr. Gurumurthy Hegde, a former student and currently a faculty at BMSCE, for being collaborators in an earlier published work that is analysed in the present manuscript.

DSSR and SKP acknowledge funding support from a SERB project (CRG/2019/001671).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Science and Engineering Research Board [CRG/2019/001671].