UMR 5672

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Flexo-electricity and electro-osmosis in the dowser texture

Pawel Pieranski (Université Paris Sud)
Flexo-electricity and electro-osmosis in the dowser texture

Spatio-temporal cross section of a wound up dowser texture submitted to an alternating electric field

Quand ? Le 04/02/2019,
de 11:00 à 12:00
Où ? Amphi. Schrödinger
Participants Pawel Pieranski
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The persistent quasiplanar nematic texture known also as the dowser texture is characterized by a 2D unitary vector field d. The orientation of the dowser field has been shown previously to be sensitive to thickness gradients (cuneitropism) and to Poiseuille flows (rheotropism). We will show now that the dowser field is also sensitive, in first order, to electric fields. This property is due: 1°- to the dielectric polarization P collinear with d expected from R.B. Meyer's considerations on flexoelectricity [1], 2°- to the electroosmosis. We have found, on one hand, that in 5CB, P is parallel to d, while in MBBA P and d are antiparallel [2]. On the other hand, directions of electro-osmotic flows in MBBA and 5CB have been found to be the same. We show also that nematic monopoles, corresponding to +2π and -2π defects of the dowser field, can be generated by flows and subsequently handled by electric fields of appropriate geometry.

References

[1] R.B. Meyer, Piezoelectric effects in liquid crystals, PRL 22, 918-921 (1969).

[2] P. Pieranski, M.H. Godinho, Flexo-electricity of the dowser texture, Soft Matter, DOI: 10.1039/C8SM02329H

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