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Understanding the Dynamics of Colloidal Particles in Biaxial Nematic Liquid Crystals

   Department of Chemical Engineering

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  Dr A Patti  Applications accepted all year round  Competition Funded PhD Project (European/UK Students Only)

About the Project

Anisotropic colloidal particles, such as rod-, plate- and board-like particles, are able to spontaneously self-assemble into a variety of liquid crystalline phases when brought in suspension. Since its first prediction in the early 1970s [1], the biaxial nematic (NB) phase, comprising two distinct optical axes, has strongly attracted the interest of the liquid crystal (LC) community and today is foreseen to be the preeminent candidate for the next generation liquid-crystal displays (LCDs) [2].

LCDs incorporate an LC layer in between two polarizing films and two electrodes. When a voltage is applied, the particles react predictably to the electric current and reorient in such a way that the polarized light crossing the LC layer can be controlled and eventually pass through the second polarizing film. The time taken by the particles to reorient is a crucial parameter affecting the performance of an LCD, which is usually quantified in terms of response time, being the time a pixel takes to go from one value to another and back to the original one. The response time is a critical parameter to measure the ability of a screen to portray clear images with well-defined edges. LCDs incorporating biaxial LCs are expected to reduce the response time because the reorientation of the particles' minor axes with an electric field should require less energy than reorienting their main axis. A remarkably stable NB phase has been recently discovered in a suspension of mineral board-like particles [3]. This pronounced stable biaxiality in between uniaxial nematic and smectic states was due to a rather significant size polydispersity, as also confirmed theoretically [4]. Such an exciting result is expected to pave the path towards the application of colloidal LCs in cutting-edge optical technology by providing LCDs with an exceptionally short response time that would further reduce motion blur. Although most of the LCDs are made of thermotropic (molecular) LCs, whose biaxial phases are still highly debated, the discovery of very stable colloidal NB phases coupled to their high thermal stability and enhanced susceptibility to external fields, make lyotropic (colloidal) LCs promising candidates for next generation LCDs.

Motivated by the impact of LCDs on our everyday life and by the appealing features of colloidal LCs, by molecular simulation and modelling we aim to unveil the dynamics of colloidal board-like particles in (polydisperse) biaxial nematic LCs and hence address their potential applicability for the next generation LCDs. More precisely, we aim to (i) predict and control the alignment of the minor and main optical axes under an applied electric field, (ii) understand how fast the minor directors rotate as compared to the main director, and (iii) study the ability of the external field to heal eventual structural defects in the material. We also aim to (iv) address how the phase behaviour is influenced by the electric field with focus on undesired phase transitions. Due to the difficulty to exclude the effect of surfaces, studying biaxial LCs is very challenging experimentally. By computer simulation, we will switch off this effect and address the dynamics under the mere effect of an electric field.

Funding Notes

Candidates should have a degree in chemical engineering, chemistry, physics or related disciplines. Familiarity on molecular simulation techniques (Molecular Dynamics and/or Monte Carlo) and experience with programming is highly desirable.

This research project is one of a number of projects in the School. It is in competition for funding with other projects. The funding is available to citizens of a number of European countries (including the UK). In most cases this will include all EU nationals. Overseas applicants are welcome to apply, but will need to apply for their own funding or pay their own tuition fees.


[1] M. J. Freiser, Phys. Rev. Lett. 24, 1041, 1970.
[2] G. R. Luckhurst, Nature 430, 413, 2004.
[3] E. van den Pol, A. V. Petukhov et al., Phys. Rev. Lett. 103, 258301, 2009.
[4] S. Belli, A. Patti, M. Dijkstra, R. van Roij, Phys. Rev. Lett. 107, 148303, 2011.
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