This project will employ molecular simulations and statistical mechanics to determine how reduced molecular symmetry impacts on phase properties. Of particular commercial interest will be high tilt angle antiferroelectric and de Vries smectic phases. It is well known that layer contraction at the Sm A - Sm C transition
leads to the formation of a chevron defect structure which is a major obstacle in the commercialisation of novel electro-optic displays based on ferro- and antiferroelectric liquid crystals.

Recently, materials with practically no layer contraction have been discovered, and we propose to develop a molecular theory of these de Vries smectic phases in order to explain their molecular structure-dependent behaviour.

The key features of real molecules can be mapped onto simple systems and their material properties investigated by means of simulation studies. Simple models with steric quadrupoles such as chiral and achiral zigzag models have been successful in simulating complex phase structures such as anti-parallel phases, cubic phases and now tilted phases. Tilted phases were obtained when the angle of rotation of the central site in the zigzag structure was increased and also when it was moved out of plane to form a chiral system (see Figure 1). This agrees with experimental evidence from Goodby that has demonstrated the importance of angle of rotation of the central aromatic group.

Figure 2 is a snapshot of a typical tilted configuration in a smectic B phase with a central site rotation of 30 degrees and Figure 3 illustrates local bond correlation order in a smectic C phase formed by chiral zigzag molecules with an additional out-of-plane rotation of 0.5 degrees.

Using information from chemical synthesis (Goodby, Merck) these methods will now be employed to investigate low symmetry chiral phases such as the antiferroelectric state as well as de Vries smectic phase. Results of simulation studies will be used to inform molecular theory and thus feed into projects 8, 9 and 10 and compared to experimental results obtained using X-ray diffraction by Profs. Gleeson and Richardson.

Johnston SJ, Low RJ, Neal MP
Computer simulation of polar bent-core molecules
PHYS REV E 66 (6): art. no. 061702 Part 1 DEC 2002

Solymosi M, Low RJ, Grayson M, et al.
Scaled chiral indices for ferroelectric liquid crystals
FERROELECTRICS 277: 483-490 2002

Johnston SJ, Low RJ, Neal MP
Computer simulation of polar rod-like molecules
FERROELECTRICS 278: 663-672 2002

Withers IM, Care CM, Neal MP, et al.
The effects of molecular shape and quadrupole moment on tilted smectic phase formation
MOL PHYS 100 (12): 1911-1924 JUN 2002

Johnston SJ, Low RJ, Neal MP
Computer simulation of apolar bent-core and rodlike molecules
PHYS REV E 65 (5): art. no. 051706 Part 1 MAY 2002

Solymosi M, Low RJ, Grayson M, et al.
A generalized scaling of a chiral index for molecules
J CHEM PHYS 116 (22): 9875-9881 JUN 8 2002

Neal MP, Parker AJ, Grayson M
Computer simulation of liquid crystalline molecular asymmetry and its link to molecular design
MOL CRYST LIQ CRYST 364: 313-322 2001

Neal MP, Parker AJ
Molecular dynamics study of mesophase formation using a transverse quadrupolar Gay-Berne model
PHYS REV E 63 (1): art. no. 011706 Part 1 JAN 2001