University of Lincoln, UK

CPG seminar on Liquid Crystals from Manchester – Christine Stokes

CPG seminar

5 th December, 2012, at 15:00 in Foster Cinema

Christine Stokes (The University of Manchester)

Christine’s talk will consist of 2 parts:

Part 1: My experience as a NoWNANO DTC student.

After a very short questions and answers session she will continue with

Part 2: Simulations of bent core molecules using molecular dynamics.

NPT_p=110_100000_color

Simulation when pressure of 110 has been applied to six component system. The system coloured according to the molecule type were the bright colours represent the center of mass of each molecule.

Liquid Crystals are a state of matter that lies between the classical liquid and solid state. What defines a liquid crystal is the long-range orientation order similar to a solid and the ability to move translationally like a liquid, which provides the ability to change their configuration. There are numerous types of liquid crystals that each have individual properties. Commonly known liquid crystals are nematic, which has a common orientation but no positional ordering, and smetic, which has a common orientation and positional ordering in one direction and random orientation in the other directions. Due to the physical and optical properties, liquid crystals have been used in technology such as liquid crystal displays of TVs and computers.

20121206-234022.jpg

Christine during her seminar in Preston

The nematic and smetic phases of liquid crystals are usual aligned along one axis so have one distinct optical axis. In some systems however, biaxial phases have been observed were alignment along both the long and short axis occurs, hence ordering in three dimensions, therefore there are three distinct optical axis. The biaxial nematic phase is expected to be a better substitute for current uniaxial nematics in liquid crystal displays.

In this project DLPOLY, a molecular dynamics simulation method, has been used to simulate bent core molecules (V-shaped) for systems consisting of 4-6 bent core molecule types which all vary by the value of the bend angle. In each of the systems, pressure has been applied which has been increased gradually to see the different liquid phases that generate.

The objective of this study was to see if using various bend angles would create a biaxial nematic phase. Currently, 4-6 component systems with a minimum variation in the angles was 5 degrees and a maximum bend angle of 160 degrees and four component systems with smaller bend angles and also larger angle variations have been simulated. The results of these systems have yet to generate a biaxial nematic however biaxial smetics have been generated. For the 4-6 component simulations isotropic, nematic, biaxial smetic, mixed smetic and crystalline phases were seen. Analysis of the other simulations is currently being done to see if a biaxial nematic phase forms.

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