Phase behaviour and Dynamics of Colloidal Liquid Crystals of Board-like Particles

Colloids consist of particles dispersed in a solvent, whose size, between 10 nm and 10 μm, is small enough to neglect sedimentation with respect to Brownian motion. Colloids can show a very intriguing phase and aggregation behaviour, surprisingly similar to that of molecular and atomic systems. This similarity has a striking relevance in materials science: it is crucial to unveil a number of dynamical processes involving atoms or molecules that are too fast to be detected via conventional microscopy, and provides the opportunity to design functional materials for advanced electro-optical devices. Colloids incorporating anisotropic particles are able to form liquid crystals (LCs), which exhibit properties in between those of crystals and fluids and are classified in terms of positional and orientational order. This project will focus on nematic LCs, showing long-range orientational order, but lacking long-range positional order. In particular, uniaxial nematic (NU) LCs have a single director indicating the preferred direction of the particles, while biaxial nematic (NB) LCs exhibit 3 orthogonal directors.

By molecular simulation, we will first map out the phase diagram of colloidal boardlike particles (BPs), extending the results we observed for monodisperse [1] and bidisperse [2] systems to polydisperse systems, where the stability of the NB phase is expected to be strongly enhanced as indicated by experiments [3] and theory [4].

In the second part of the project, we will focus on the dynamics of these systems and assess the effect of dynamical heterogeneities, collective motion and formation of transient clusters on the structural relaxation decay of the NB phase when an external field is switched on. One of the aims is to follow the rearrangement of the NB phase and how the eventual occurrence of these phenomena might influence its response time and final structural order. Insight into the kinetics of reorientation of the NB phase and into its dependence on the presence of transient clusters upon the on/off switching of an external field, will be crucial to grasp the physics underpinning any potential use of molecular LCs of biaxial nematics in display applications.

The successful candidate will develop computational models to simulate the phase behaviour and dynamics of colloidal suspensions of anisotropic particles. The applicant should be familiar with programming (e.g. Fortran) and ideally have a knowledge of the Monte Carlo molecular simulation technique [5,6].

Applicants should have or expect to achieve at least a 2.1 honours degree in Physics, Chemical Engineering, Chemistry or a related subject.

Successful candidates will be enrolled in the 3-year Ph.D. program of the School of Chemical Engineering and Analytical Science.