Electron microscopy of polymer-carbon nanotubes composites

Characterization of polymer nanocomposites by electron microscopy has been attempted since last decade. Main drives for this effort were analysis of dispersion and alignment of fillers in the matrix. Sample preparation, imaging modes and irradiation conditions became particularly challenging due to the small dimension of the fillers and also to the mechanical and conductive differences between filler and matrix. To date, no standardized dispersion and alignment process or characterization procedures exist in the trade. Review of current state of the art on characterization of polymer nanocomposites suggests that the most innovative electron and ion beam microscopy has not yet been deployed in this material system. Additionally, recently discovered functionalities of these composites, such as electro and photoactuation are amenable to the investigation of the atomistic phenomena by in situ transmission electron microscopy. The possibility of using innovative thinning techniques is presented. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Tailoring the electrical properties of carbon nanotube-polymer composites

Advances in functionality and reliability of nanocomposite materials require careful formulation of processing methods to ultimately realize the desired properties. An extensive study of how the variation in fabrication process would affect the mechanism of conductivity and thus the final electrical properties of the carbon nanotube-polymer composite is presented. Some of the most widely implemented procedures are addressed, such as ultrasonication, melt shear mixing, and addition of surfactants. It is hoped that this study could provide a systematic guide to selecting and designing the downstream processing of carbon nanocomposites. Finally, this guide is used to demonstrate the fabrication and performance of a stretchable (pliable) conductor that can reversibly undergo uniaxial strain of over 100%, and other key applications are discussed. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Multi-colour switching of polymer stabilized chiral nematic liquid crystal devices

We have fabricated a series of polymer stabilized chiral nematic test cells for use as flexoelectro-optic devices. The devices fabricated were based on commercial chiral nematic mixtures which were polymer stabilized so as to enhance the uniformity and stability of the uniform lying helix texture in the cells. During fabrication and test procedures a series of unusual scattering states have been observed within the devices at different viewing angles. The observations made so far indicate that the properties of the scattering state lies somewhere between the focal conic texture and the Grandjean or planar texture and that the devices exhibit both a helical pitch selective reflection and scattering effect. What is even more dramatic is that the wavelength selectivity of the scattering effect can be tuned by an applied field. In addition, we show that it is possible to achieve good uniform lying helix textures from such devices. Moreover, we show that in certain cases the spontaneous alignment of the helix in the plane of the device opens up the possibility of a new mode of switching. Flexoelectric, Redshift, Coloured scattering, Liquid crystal, Polymer-stabilized liquid-crystal;.