8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P3.8Fri 911:10-14:00Electro-optic response and X-ray orientational analysisof anisotropic colloidal liquid crystal particles withapplied electric fieldRobert Greasty, 1 Susanne Klein, 1 Jana Heuer, 2 and Claire Pizzey 31 HH Wills Physics Laboratory, Tyndall Avenue, BS8 1TL, Bristol, United Kingdom2 HP Labs, Bristol, United Kingdom3 Diamond Light Source Ltd, Didcot, United KingdomAnisotropic colloidal pigment particles have been studied in both isotropic and anisotropicsolvents. Azo dye particles known as Permanent Rubine were studied. They have a colour indexof pigment red 57:1 [1]. The particles are platelets with a mean length, width, and thickness of280, 130, and 10nm respectively. The particles have been stabilized in organic solvents usingthe commercially available polymeric stabilizer Solsperse 11200. They have also been stabilizedusing mesogenic precursors both in organic solvents and in liquid crystal hosts. The absorption ofthe pigment suspensions were shown to decrease with applied electric field, leading to a visibletone change (Figure 1). X-ray scattering was then used to determine the underlying cause ofthis behavior. The I22 beamline at the diamond light source was used to follow the plateletorientation by observing the particle form scattering. This shows that the particles rotate underthe influence of the electric field so that their smallest dimension aligns perpendicular to the field.The alignment of a Bragg diffraction peak from the lattice planes at Q=0.35 Å demonstrates thatthe internal lattice plane normals align perpendicular to the applied electric field (Figure 2) [2].The degree of alignment of the lattice plane normals can be quantitatively analyzed to determinean order parameter for the particles themselves. This reorientation accounts for the decrease inthe absorption relative to the applied electric field. The degree of alignment of the mesogenicstabilized particles was dramatically increased in the presence of the liquid crystal host (Figure2). This gives near perfect orientational order of the platelets and a greater decrease in absorptionwith electric field.[1] Society of Dyers and Colourists Colour Index, Bradford, 3, 3308 (1971-1977)[2] J. Connolly, et al. , Journal of Physics: Condensed Matter 19, 156103 (2007 )8