Electric field nematic alignment of fluorohectorite clay particles in oligomeric matrices
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né C. Castberg Physics Department, University of Oslo, 0316, Oslo, Norway
Alexander Mikkelsen Department of Physics, NTNU, 7491 Trondheim, Norway
Jon Otto Fossumb) Department of Physics, NTNU, 7491 Trondheim, Norway; and The Centre for Advanced Study (CAS), Norwegian Academy of Science and Letters, 0272, Oslo, Norway (Received 4 December 2012; accepted 4 April 2013)
We study the behavior of fluorohectorite synthetic clay particles dispersed in paraffin wax. We report wide-angle x-ray scattering related to electric-field-induced alignment of the embedded clay particles. The development of anisotropic arrangement of the particles is measured during melting and crystallization of the composites. The degree of anisotropy is quantified by fitting azimuthal changes of the clay diffraction peak intensity to the Maier-Saupe function. This parametric function is then used to extract both the full width at half maximum (FWHM) and the amplitude of the anisotropic scattering and eventually to estimate a nematic order parameter for this system. Finally, the time evolution of the one-to-zero and zero-to-one water layer transition in paraffin embedded fluorohectorite clay galleries is presented, and we demonstrate that such particles can be used as “meso-detectors” for monitoring the local water content in bulk carrier matrices, such as paraffin wax.
I. INTRODUCTION
Clay particles have the ability to change and improve many physical properties, e.g., mechanical strength, thermal stability, conductivity, etc. of the medium in which they are suspended.1–3 Some of these properties can be anisotropically enhanced if the particles are orientationally aligned in the host medium. Such a particle organization can be utilized as a molecular barrier, i.e., the permeability of gas molecules in polymer–clay composites are significantly reduced in the direction normal to clay platelet surfaces, whereas no change is expected for molecules propagating along the oriented clay surfaces. Yano et al.4 report that only a 2 wt% addition of montmorillonite clay particles into polyimide may lower the gas permeability down to a value less than half of the pure polyimide gas permeability. Alignment of clay particles can be induced by planar shearing,5 extrusion,6 gravity,7 and magnetic8 or electric field.9 An electric field is often used to produce anisotropic structures to obtain desirable physical properties.
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2013.104 J. Mater. Res., Vol. 28, No. 10, May 28, 2013
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When polarizable particles are exposed to an electric field of either alternating current or direct current, dipoles will be induced and result in a rotational force on the particles in accordance with the Clausius–Mossotti relation.10 The particle alignment can be monitored by means of x-ray or neutron diffraction,11,12 and the degree of anisotropy can be quantified and expressed in terms of an order parameter S2 (Refs.
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