Rebecca Walker

Project Title: Chirality and the Twist-Bend Nematic Phase

Liquid crystals constitute the fourth state of matter and have properties intermediate between those of a crystalline solid and a liquid. They flow like a liquid, but have some degree of molecular ordering like a crystal, and are perhaps best known for their use in liquid crystal displays. Different liquid crystal phases exist, depending on the degree of molecular ordering present. The simplest, and technologically most important, is the nematic phase in which the molecules all lie in the same direction, known as the director, while their centres of mass are randomly distributed. Recently, however, it has been discovered that bent molecules can form a nematic phase with a different structure. The bent molecules have a tendency to cause the director to bend, but such an arrangement cannot fill space efficiently. To compensate for this, the director twists forming a helical structure in which the director is tilted with respect to the helical axis. The phase is not chiral because both right- and left-handed helices form with equal probability. This is the twist-bend nematic phase. The proposal addresses the intriguing question as to what happens if the bent molecules are made chiral. This will favour the formation of just one type of helix and so the phase will become chiral. This would constitute a new type of liquid crystal phase. The proposed research involves the synthesis and characterisation of a range of novel chiral liquid crystals designed to exhibit the twist-bend nematic phase. The research will significantly enhance our understanding of the relationships between molecular structure and the observation of this new phase.