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Understanding the Dynamics of Colloidal Particles in Biaxial Nematic Liquid Crystals


Project Description

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 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.

Since its prediction in the 1970s, the NB phase has strongly attracted the interest of the LC community, especially for its appealing applications in LC displays. Unfortunately, the existence of the NB phase at temperatures generally suitable for most display applications is still highly debated. The recent experimental observation of a remarkably stable NB phase of colloidal boardlike particles (BPs) is stimulating new interest on this phase, justified by its potential use in displays with shorter response time. However, prior to exploring the feasibility of this challenging technology, it is crucial to acquire a full picture of the laws underpinning the equilibrium and dynamical properties of colloidal NB phases, whose fundamental understanding constitutes the aim of this project.

By molecular simulation, we will seek the fundamental know-how to rationally ponder the potential of NB phases in future display devices. In particular, we will map out the phase diagram of colloidal BPs and determine the stability range of the NB phase, being strongly enhanced by polydispersity as indicated by experiments and theory. This task is particularly challenging due to the extension of the phase space to explore, but will be addressed by a scientific workforce relying on a specific expertise in molecular simulation and significant human resources. To better understand the formation of the oblate and prolate NU phases, we will study their nucleation from the isotropic (I) phase and calculate the nucleation barriers and the morphology of the growing nuclei at different supersaturations. This is chellenging because the I-N are weakly first-order transitions, but crucial to have an insight into the kinetics of reorientation of BPs. Phase equilibrium and transition are expected to be modified by an external field, whose effect will be addressed for its crucial role in practical applications involving the reorientation of the NB phase.

In the second part of the project, we will focus on the effect of dynamical heterogeneities, collective motion and formation of transient clusters on the 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 biaxial nematics in display applications.

Funding Notes

Applicants should have or expect to achieve at least a 2.1 honours degree in Chemical Engineering, Chemistry, Physics or related disciplines. Familiarity with molecular simulation techniques (Molecular Dynamics and/or Monte Carlo) and experience with programming is highly desirable. Excellent written and oral communication skills in English are required.

This research project is one of a number of projects in the School. It is in competition for funding with other projects.

If you wish to apply for this project, please choose 'PhD Chemical Engineering and Analytical Science' from the list of available programmes.

How good is research at University of Manchester in Aeronautical, Mechanical, Chemical and Manufacturing Engineering?
Chemical Engineering

FTE Category A staff submitted: 33.90

Research output data provided by the Research Excellence Framework (REF)

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