Document Type

Thesis

Publication Date

1994

Abstract

Two projects have been investigated in this thesis. One is the transport of ion charges in surface stabilized ferroelectric liquid crystals (SSFLCs), and the other is the coupling of molecular reorientation and mass flow in ferroelectric liquid crystals (FLCs).

Ion transport equations have been set up and solved numerically, and the results agree qualitatively with measurements of current response to applied AC voltage with DC offset. By using a simple model, we clarify the fact that the measured current is different from the ionic flow current at the interfaces. Our calculation shows that, in cells with insulating alignment layers, due to the existence of ions, the fields at the interfaces can be many times larger than applied field.

In liquid crystals flow and molecular orientation are coupled, e.g., the reorientation of the molecules will induce flow, which in turn will affect the molecular reorientation. We expect that this coupling between flow and molecular reorientation be strong in FLCs since the switching in FLC is fast and in SSFLC the flow is more confined. We first derive the elasto-hydrodynamic equations for coupled reorientation and flow in FLCs, starting from Leslie, Stewart and Nakagawa's continuum theory for smectic C liquid crystals. Comparisons with nematic-like dynamic equations are made and the equations are applied to the SSFLC cells. We solve the elasto-hydrodynamic equations numerically and compare the results to the case in which the flow effects are neglected.

Our simulations show that flow generally makes the switching faster in the case of the dipoles being in an unstable equilibrium state in an applied field . Our calculations show that it is important to include the backflow in the reorientation dynamics in order to have the correct switching picture.

We also provide direct experimental evidence to show that mass flow may be generated by molecular reorientations , which we call the "pumping effect". By applying a AC electric field to an SSFLC cell, we are able to completely expel the FLC from a cell. We also use computer simulation to explain the pumping effect qualitatively.

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