EPJ E Highlight - Dowsing for electric fields in liquid crystals

Following the change in orientation of the molecules in the dowser texture yields a shape that resembles the wooden dowsing rods used in previous centuries to locate groundwater. Left: © Pawel Pieranski, Right: Dowsing#/media/File: 18th_century_dowser.jpg

The orientation of the ordered molecules that make up nematic liquid crystals can change under electric fields, and can be used to detect subtle electrical effects.

You may not know it, but you probably spend several hours a day looking at nematic liquid crystals; they are used in virtually every smartphone, computer and TV screen. They are liquids composed of elongated molecules, which in some situations can be oriented in a curious way termed the 'dowser texture', which is sensitive to external conditions. Physicists Pawel Pieranski of the Universite Paris-Sud, Paris, France and Maria Helena Godinho of Universidade Nova de Lisboa, Lisbon, Portugal have now published a paper in EPJ E that shows that the dowser texture responds to electric fields in different ways in different nematic materials.

In a dowser texture, a liquid crystal is squeezed between two glass plates so that the molecules closest to the plates are perpendicular to them but point in opposite directions. In the bulk, on the way from one plate to the other one, the molecules rotate 180° so that if you follow the change in their direction with a line you end up with a pointed shape resembling the Y-shaped wooden rods used by dowsers in centuries past to locate groundwater, hence the name – the dowser texture.

The 'tip' of the dowser texture is free to rotate rather like a weathervane and can thus act as a sensitive probe. Its direction is sensitive to the direction of an electric field, with the tip pointing either from the positive to the negative electrode (parallel) or vice versa (antiparallel).

In their work, Pieranski and Godinho observed different dowser textures in electric fields under polarised light and showed them to be antiparallel to the field in the liquid crystal MBBA, which is in line with previous experiments, but unexpectedly parallel in 5CB. They explained this in terms of the phenomenon of 'electro-osmosis': a liquid flow that is induced by an electric current. Thus, the dowser texture can also be used to detect electro-osmosis.

Pieranski and Godinho also found that the dowser texture can contain defects, which they suggest may have applications as microscopic carriers.

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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