The response of anisotropic pigment particle suspensions to externally applied electric fields has been explored for possible application in reflective display technologies. Three different types of pigment particle were suspended in dodecane using a polymeric stabiliser and showed Schlieren textures between crossed polarisers at high concentrations (>25-30 wt%), indicating the formation of colloidal nematic phases. Orientational order parameters were determined by X-ray scattering and the influence of polydispersity on the values is discussed. X-ray scattering measurements also demonstrated a change in the structure factor consistent with the onset of a colloidal nematic phase. In addition, the pigment particles were dispersed into various liquid crystal hosts at low concentrations (<5 wt%) with and without the presence of mesogenic mimic stabilisers. However, the influence of these stabilisers on orientational ordering could not be confirmed. The electro-induced ordering determined via scattering was related to the electro-optical response of each suspension using a simple model. The particles in nematic hosts showed a high degree of orientational ordering at lower electric field strengths but also showed a reduction in stability. Although these systems have shown strong orientational ordering, the optical response has been limited by the intrinsic shape of the pigment particles and the distribution of the transition dipoles moments within them. Nevertheless, the feasibility of developing materials for display applications has been demonstrated.
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