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Esther van den Pol

Van’t Hoff Laboratory for Physical and Colloid Chemistry
Utrecht University, The Netherlands

Colloidal dispersions of goethite (α-FeOOH) contain boardlike crystallites (of volume L×W×T) which form nematic, smectic and columnar liquid crystals [1]. These goethite particles also display peculiar magnetic properties [2] combining a considerable permanent magnetic moment along their length (L) with an induced magnetic moment along the shortest particle dimension (T). Therefore, particles align parallel to a small external magnetic field but perpendicular to a large magnetic field.

We here present a goethite dispersion, for which L/WW/T, so that a biaxial nematic phase might be expected. Small Angle X-ray Scattering (SAXS) measurements revealed that both a biaxial nematic and smectic phase are observed in this system. The biaxial phases could be aligned in different directions by applying a very small magnetic field which allowed us to construct a complete picture of the biaxial phases.

 

 

SAXS patterns of a biaxial nematic phase in zero field and in a 40 mT field directed into the image.

References

  1. G. J. Vroege, D. M. E. Thies-Weesie, A. V. Petukhov, B. J. Lemaire, P. Davidson
    Adv. Mater. 18, 2565 (2006).
  2. B. J. Lemaire, P. Davidson, J. Ferré, J. P. Jamet, P. Panine, I. Dozov, J. P. Jolivet
    Phys. Rev. Lett. 88, 125507 (2002).