Prof Maureen P Neal

Research interests lie in the field of simulation and theoretical studies of condensed matter at the molecular level with particular application to the field of liquid crystals. Recent theoretical work has proposed chiral indices which link molecular and phase properties. Again, recently, advances in simulation algorithms have been made using symplectic methods. There is a range of publications from the group covering all these areas.

The liquid crystal research group currently comprises R.Low@coventry.ac.uk (Website) and H.Kamberaj@mmu.ac.uk.  Recent students are S. Johnston and M. Solymosi.

Typical liquid crystal molecules are shown below. Molecules such as TBBA that form a smectic C phase have a zigzag geometry.

Minimised structure for TBBA using the Biosym package in filled form and in stick form

The achiral phenylpropriolate shown below forms an antiferroelectric-like phase on cooling. It has an overall triangular lath-like shape.

Snapshot of a typical configuration of the smectic phase for the triangle geometry

Key features of real molecules identified by statistical mechanics can be mapped on to simple systems and their phase and material properties investigated by means of simulation studies. Early simulation studies were undertaken of a steric model and of an electric model.

Simulation Studies

The steric study comprised a comparison of two models: a zigzag and a triangle model formed from three rigidly joined Gay-Berne sites. This led to the first simulation of an anti-parallel phase, shown here. The zigzag model demonstrated a rippled structure but no overall tilt in the layers was seen at this stage

The second simulation study investigated the addition of a longitudinal electric quadrupole to a single-site Gay-Berne molecule, and was found to lead to the simulation of a smectic C phase seen here. This is of particular importance in molecular design. In contrast when a transverse electric quadrupole was added cubic smectic phases were stabilized rather than the more usual hexagonal smectic B phases

Tilted phases were obtained in the simulation of the zigzag model, a steric quadrupole, when the angle of rotation of the central site was increased. When it was moved out of plane to form a chiral system, as shown in the simple model illustrations opposite, a smectic C phase was obtained.

This agrees with experimental evidence that has demonstrated the effect of angle of rotation of the central aromatic group with a link established between the angle of rotation and large phase tilt angle molecules with a central site rotation of 30^o and with an additional out-of–plane rotation of 0.5.

The graph shown here illustrates local bond correlation order in a smectic C phase. The movie clip here shows the time evolution of the smectic C phase.

Animated movie clip.(6.83 MB) Right click to download.

Chiral indices

Chirality plays an important role in phase structures of many materials and is a key molecular characteristic. The challenges of moving from a statement that a molecule is chiral to a quantitative measure of chirality and to providing a link between molecular chirality and bulk phase characteristics such as the pseudoscalar helical twisting power  have been addressed in part with the development of a scaled chiral index.

This provides a measure of the contribution of each atom to the overall index as shown for biphenyl, two binapthyl derivatives and two ferroelectric molecules as illustrated here. A high correlation has been found between the scaled index and helical twisting power for a range of chiral dopants.

Comparison with theories of Nordio et al shows similar predictive power for a range of helicene and binapthyl derivatives as shown in the graph here.

Symplectic and/or  Time reversible Algorithms

Algorithms have been developed   allowing the time step to be increased up to 0.0025 (in reduced units) with an insignificant drift shown apparently.

A list of my publications and current research projects is to be found here

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