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

P3.12Fri 911:10-14:00The influence of suspended nano-particles on theelectro-optical behaviour of liquid crystalsSusanne Klein, 1 Robert Greasty, 1 Robert Richardson, 2 and John Rudin 11 HP Labs, Long Down Avenue, BS34 8QZ, Bristol, United Kingdom2 HH Wills Physics Laboratory, Bristol, United KingdomIn recent years there has been considerable experimental and theoretical interest in suspensionsof ferroelectric particles in liquid crystal hosts such as 5CB. These suspensions have shownsubstantial increases in permittivity relative to the pure nematic host [1]. To explore the relationshipbetween particle dynamics and material properties and rationalise the permittivityeffects, we followed the preparation steps given in [2] (we included a washing step to avoidionic contamination of the liquid crystalline host) and prepared Barium Titanate suspensions in5CB. We failed to reproduce the effects described in the literature and we have evidence that thewashing step removed the stabilizer from the particles. We decided to explore a wider range ofparticles and stabilisers to establish a model for changes in permittivity and ferroelectricity ofthe suspensions. Our test particles were Silica aerosils (Evonik), Manganese Ferrites (Shepherd),Titanium Dioxides (DuPont) and Barium Titanate (Sigma Aldrich). The particles were treatedwith different stabilisers and their permittivity and electro-optical response was measured indifferent isotropic and liquid crystalline hosts. Our results so far show that the permittivity ofthe suspensions is very sensitive to the surface treatment of the particles. For example whenTitanium Dioxide particles (e = 86 to 173) at small volume fractions disorder the nematic phase,the permittivity of the suspension is lower than the field aligned pure nematic. If the particles arewell integrated in the nematic matrix the permittivity will exceed that of the pure host.[1] O. Buchnev et al. , Mol. Cryst. Liq. Cryst. , 422, 47 (2004)[2] Y. Reznikov et al. , Appl. Phys. Lett. 82, 1017 (2003).12