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Instruments / Technical Area	Publication Details	Published
I22-Small angle scattering & Diffraction	Liquid crystalline phases in suspensions of pigments in non-polar solvents Susanne Klein , Robert M. Richardson , Alexey Eremin DOI: 10.1142/9789814619264_0026 Show Abstract ▼ Abstract: We will discuss colloid suspensions of pigments and compare their electro-optic properties with those of traditional dyed low molecular weight liquid crystal systems. There are several potential advantages of colloidal suspensions over low molecular weight liquid crystal systems: a very high contrast because of the high orientational order parameter of suspensions of rod shaped nano-particles, the excellent light fastness of pigments as compared to dyes and high colour saturations resulting from the high loading of the colour stuff. Although a weak ‘single-particle’ electro-optic response can be observed in dilute suspensions, the response is very much enhanced when the concentration of the particles is sufficient to lead to a nematic phase. Excellent stability of suspensions is beneficial for experimental observation and reproducibility, but it is a fundamental necessity for display applications. We therefore discuss a method to achieve long term stability of dispersed pigments and the reasons for its success. Small angle X-ray scattering was used to determine the orientational order parameter of the suspensions as a function of concentration and the dynamic response to an applied electric field. Optical properties were investigated for a wide range of pigment concentrations. Electro-optical phenomena, such as field-induced birefringence and switching, were characterised. In addition, mixtures of pigment suspensions with small amounts of ferrofluids show promise as future magneto-optical materials.	Dec 2016
I22-Small angle scattering & Diffraction	Stability and orientational order of gold nanorods in nematic suspensions: a small angle X-ray scattering study M. R. Thomas , J. Hallett , S. Klein , S. Mann , A. Perriman , R. M. Richardson Molecular Crystals And Liquid Crystals 610, 44 - 50 25th International Liquid Crystal Conference (ILCC 2014) DOI: 10.1080/15421406.2015.1025204 Diamond Proposal Number(s): [7575] Show Abstract ▼ Abstract: Stable suspensions of gold nanorods in 4-cyano-4′-pentylbiphenyl (5CB) have been prepared by capping the nanoparticles with polyethylene glycol (PEG). Small angle X-ray scattering has been used to characterize the orientational order of the gold nanorods and the properties of any aggregates. It was found that the nanorods had a very high degree of orientational order with respect to the director of the 5CB matrix and this could be redirected by an applied electric field at 2kHz. Two different PEG molecular weights were investigated and it was found that the lower (1.9kDa) gave exceptionally high order parameters, above 0.9.	Jul 2015
I22-Small angle scattering & Diffraction	Electro-induced orientational ordering of anisotropic pigment nanoparticles Robert Greasty , Robert M. Richardson , Susanne Klein , David Cherns , Michael R. Thomas , Claire Pizzey , Nicholas Terrill , Cyrille Rochas Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences DOI: 10.1098/rsta.2012.0257 Show Abstract ▼ Abstract: 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 stabilizer, and showed Schlieren textures between crossed polarizers at high concentrations (greater than 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 (less than 5?wt%) with and without the presence of mesogenic mimic stabilizers. However, the influence of these stabilizers 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 not only 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.	Mar 2013
I22-Small angle scattering & Diffraction	Nematic director-induced switching of assemblies of hexagonally packed gold nanorods Michael R. Thomas , Susanne Klein , Robert Greasty , Stephen Mann , Adam W. Perriman , Robert M. Richardson Advanced Materials 24 (32), 4424 - 4429 DOI: 10.1002/adma.201201319 PMID: 22761047 Diamond Proposal Number(s): [7575] Show Abstract ▼ Abstract: Self-assembled disc-shaped clusters of hexagonally packed, thiol-functionalized gold nanorods are prepared and dispersed in thermotropic nematic liquid crystals. The resultant hybrid complex fluids exhibit colloidal anisotropy with very high orientational order and are characterized by SAXS as shown in the figure. Precise, reconfigurable control of the cluster orientation at very low electric field strengths (0.18 V μm−1) is achieved.	Aug 2012
I22-Small angle scattering & Diffraction	Electric field induced orientational order in suspensions of anisotropic nanoparticles Robert Greasty , Jana Heuer , Susanne Klein , Claire Pizzey , Robert Richardson Molecular Crystals And Liquid Crystals 545, 133/[1357] - 145/[1369] DOI: 10.1080/15421406.2011.568888 Show Abstract ▼ Abstract: Suspensions of anisometric dye particles in dodecane have been investigated by electro-optic methods and X-ray scattering. The suspensions have nematic like properties such as a Schlierren texture and an electro-optic response. The thin, plate-like, particles of Permanent Rubine are crystalline monodomains with a set of lattice planes spaced by 18 Å lying parallel to their largest faces. They are oriented by an electric field such that their normals tend to be perpendicular to the applied field. The stronger ordering at about 25 wt% suggests that this might be the onset of the nematic phase. A simple model shows that the electric field induced change in optical absorbance is consistent with the induced orientational order.	Jun 2011

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