What is it about nature that we find so beautiful? Maybe it is its colours and compositions, or the emotions and thoughts it provokes. This book will explore not only the vibrant visual aesthetic of liquid crystals, but also the deeper beauty that emerges as we come to understand their science and involvement in life.
The often untold story of liquid crystals lies somewhere between chemistry and biology. Most people are familiar with phase transitions like those between ice and water, and water and steam. In some materials, which are common in biological systems, there exist extra phases of matter called liquid crystals. Unlike crystals or liquids, they have a unique combination of fluidity and structure that enables them to spontaneously self-assemble into complex forms while remaining sensitive to environmental changes—key features of biological machinery—with mesmerising visual effect when viewed under a polarising optical microscope. Their fluid clockwork has been critical to the functioning of every biological cell since life began. The lipids, proteins, DNA and chromosomes in your body silently play out their dramas hundreds of billions of times every day.
Considering the shape-shifting, dynamic forms of liquid crystals when viewed under a microscope, it is not surprising that early researchers thought they may be some form of life. Over the last handful of generations, scientists have uncovered many different types of liquid crystals. We have come to understand why they exist, the laws that govern how they interact with themselves, with other materials, with light, and with fields. We have found them in the silk dope of spiders and worms, in the membranes of biological cells and many other biological systems. Chemists have engineered liquid crystals to exhibit new and unusual physical properties. And we have exploited liquid crystals in technology, mainly, thus far, for liquid crystal displays (LCDs) such as those in television and smartphone screens. It turns out that evolution has also worked out how to use liquid crystals for display purposes, as in the iridescence of beetles. We, however, have only just begun to understand the wider implications of imitating how biology exploits liquid crystals for our own technology.
Most people first hear the term 'liquid crystal' in relation to LCDs. Under normal circumstances, the kinds of liquid crystal structures useful for technology tend to be uniform, controlled, stationary, and boring. Some, out of curiosity, may have poked the screens of computers and calculators and been delighted by the strange liquid-like behaviour they saw. By making them flow, a fascinating aspect of their behaviour is revealed. The pretty structures you see throughout this book have come out of the same impetus of curious exploration, taking liquid crystals into conditions that are outside of their use in technology. Messing around with floating pools of liquid crystal near their melting temperature, inducing flow, adding additional chemicals like detergent, and playing with unusual liquid crystal phases—misspent hours of mucking around doing things you're not supposed to just for the thrill of seeing nature doing something intricate and amazing.
In chapter 2 we will build a basic understanding of matter, from the sub-atomic world of quarks to the solids, liquids and gases we experience in everyday life, and we will come to understand what a liquid crystal is. Chapter 3 will introduce light, and how it interacts with matter. These first chapters will form the basis upon which we will understand how matter can produce the images in this book. The remainder of the book chapters will explore the unique features and visual qualities of a series of different liquid crystals. Chapter 4 will explore nematic liquid crystals. The molecular properties that lead to the special physical properties of nematics are discussed. We will introduce key concepts related to the topology and symmetry of liquid crystals, and describe how they are used in LCD technology. Chapters 5 and 6 will introduce the concept of chirality in liquid crystals and explore a range of phenomena related to the twisted structures they form at different length scales. Chapter 7 follows, describing a range of less common and more complex structures, including the cubic-structured blue phases, the lyotropic liquid crystals most commonly seen in biological systems, and the layered smectic and twist-grain-boundary phases, and we will describe how spiders exploit liquid crystals to produce silk with extraordinary physical properties. Finally, chapter 8 will explore the discotic and columnar liquid crystal phases. On our journey, we will learn how liquid crystals interact with light and electric fields, the wonderful structures that liquid crystals can form, and some ways in which biology exploits the unique properties of liquid crystals.