Nano-objects - sculpting and shape in molecular material design (The Pierre Gilles de Gennes ILCS prize lecture)

ABSTRACT

Early liquid crystal compounds often had relatively simple molecular structures, but with the invention of electro-optical devices, the design of materials became increasingly important. Property-structure correlations have promoted computer-aided rational design to the point where it is becoming a necessity in the selection of compounds for preparation. For simple molecular architectures, allowable electrostatic interactions in the face of steric repulsion were used in a phenomenological way to generate new mesophases, such as the hexatic phase, and to engineer materials with desirable physical properties. Materials chemists, in the creation of substances of greater complexity, have built upon these forms of research. Interestingly, the larger the system often the more simply it becomes as the molecular bulk and shape begin to dominate over the surface interactions. Nano-objects of unique shapes, such as ‘Janus’ grains, created in the process of design can kindle the formation of new mesophases, such as the twist-bend and splay phases generated through the crowding of molecular particles, and minimisation of the free volume. This article explores the development of the shapes of molecular grains and the mesophases they spawn.

GRAPHICAL ABSTRACT

KEYWORDS:

• Hexatic
• TGB
• NTB
• splay nematic
• supermolecule

Acknowledgments

The author thanks Drs Stephen Cowling, Isabel Saez, Richard Mandle, John Moore, Laurence Abbott, Mike Hird, Robert Lewis, Valeri Vaschenko, Tingjun Zhong for their support and collaborations over the years.

Disclosure statement

No potential conflict of interest was reported by the author.

Dedication

This paper is based on the lecture given at the 2018 International Liquid Crystal Conference in Kyoto, Japan. I dedicated the lecture to my friend and work colleague Pat Cladis who had recently passed away. Apart from her outstanding contributions to the science of liquid crystals, as described in her obituary  by Brand and Pieranski, Pat greatly influenced our community through her support of many of our young researchers. When I was President of ILCS Pat was my Chair of the ILCS Awards Committee. Pat’s lead and continued support of the Glenn Brown Prize Program proved to be important to our graduating researchers, and the care she gave to them throughout the Awards ceremonies, and beyond into their careers greatly benefitted the general health of our Liquid Crystal family. Then recently, I learned of the passing of Alan Leadbetter. Alan, like Pat, I had known for over 40 years. Alan was the first scientist working on liquid crystals that I came to know outside of Hull University. He was my PhD examiner and along with George Gray my first post-doctoral supervisor. As described in this paper, through Alan we came to realise that there were two smectic B phases. I often used to write to him about what is now known as the crystal B phase, calling it a modulated B phase, and it was through this work I ended up at Bell Laboratories working on hexatics. Alan was a totally unfazed person to work with; he took things like me losing half of the deuterated pivalonitrile I was making for him in his stride. In those days it cost more than my salary. Because of Alan’s modesty, over the years I came to realise just how important his studies were on the fundamentals of structure in liquid crystals. Indeed he was truly a great scientist. Looking back, I was incredibly fortunate to work with, and for both of, these remarkable people, who sadly are no longer part of the fabric of my life and that of liquid crystals in her obituary.

Additional information

Funding

The author is indebted to the EPSRC for its support of his research through the following grants: EP/J007714/1, EP/K039660/1 and EP/M020584/1, and Platform Grant No. EP/D055261/1; and to the Leverhulme Trust; European Science Foundation; The Wild Fund of the University of York; Defence Evaluation Research Agency and QinetiQ; Kingston Chemicals Ltd.