Ionic Interface-effects in Electro-optical LC-cells

• Published in: Molecular crystals and liquid crystals (Philadelphia, Pa. : 2003) Pa. : 2003), 2002-01, Vol.375 (1), p.659-677
• Main Author: Sierakowski, Marek
• Format: Article
• Language: English
• ISSN: 1542-1406; 1563-5287
• DOI: 10.1080/10587250210568

The work discusses ionic electrode processes in LC-cells driven by voltage. Ions in LC-material are generated by dissociation of residual impurities or (dye) additives, but by ageing of LC-material as well. Therefore even in carefully purified electro-optical cells temporal decomposition of the base material causes slow, but permanent increase of ion concentration. It is apparently manifesting in non-linear electrical response of LC-cell in the case of quick switching by pulse driving. Every change of voltage on cell electrodes induces re-charging process and causes flow of the space-charge limited current across LC-layer. Existence of the ions influences electro-optical performance of LC-cell. The ionic flow changes field distribution in LC-layer and can temporary distort molecular ordering. Ionic processes may superimpose an undesired intrusion on optical switching response of LC-cell and may result either in faster or in slower switching, depending on driving source parameters. In this paper we propose a simple model of ionic processes to explain the mechanism of non-linear ionic polarisation. Observed voltage - polarisation characteristics, space-charge current flow and an anomalous electro-optical behaviour of LC-cell can be explained by the model assumed. Concentration of the considered ions, their mobility, and activation energy is also evaluated.