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Séminaire Esther van den Pol

Biaxial phases in colloidal dispersions of goethite


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).