Friday, 19th May 2006 at 3.00 pm (117 Hess Conference Room). Please check the details below:

Presentation by: Hemang Shah

Research Advisor: Adam Fontecchio

Topic: "Optical Data Storage using Liquid Crystals and Polyvinylidene Fluoride (PVDF)"

Description: Polyvinlylidene Fluoride (PVDF) is a material that has an inherent distribution of dipoles due to its chemical structure. Addition of copolymers and/or electrical modification of the material make it possible to attain the ferroelectric phase in PVDF. We investigate the influence of the polarization profile in thin films of PVDF polymers on liquid crystal (LC) alignment for the development of optical memory devices.

Previously, we have reported the creation of an analog display based on 5CB deposition on spin-coated films of PVDF and its copolymers with Trifluoroethylene (TrFE) and Hexafluoropropylene (HFP). For this work, we have used corona poling to induce the ferroelectric phase in the polymer films. The application of high electric fields rotates the dipoles in the polymer structure. On the removal of the field, a stable ferroelectric phase with remnant polarization is obtained. The ferroelectric phase was verified using Fourier Transform Infrared (FTIR) Spectroscopy.

The liquid crystal 5CB is used in its nematic state. It is deposited over the poled films in a sandwich cell arrangement and the LC alignment is observed using polarized optical microscopy. The LC alignment depends on the polarization in the polymer film. Thus, an optical memory is created with the “data” stored as ferroelectric polarization, and the readout is provided by the LC state. On application of electric fields to the cell, the internal field of the polymer layer inhibits the LC rotation. Thus, a higher threshold of LC switching is realized through the poling process indicating the locking of LC alignment.

We look forward to your participation in the same.