Abstract
Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25–60 oC) and frequency range (100 Hz–2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB.
Highlights
Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic fluid media
We investigate the dielectric behaviour of different average size ranges of the GO microparticles suspended in isotropic solvents, as well as a standard thermotropic nematic liquid crystal, 5CB
We present systematic dielectric spectroscopy results of GO in different phases, at varying temperature and for different GO sizes
Summary
Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. The self-assembly of GO flakes in isotropic media (often water) has been found to result in a lyotropic nematic liquid crystal when the concentration of the GO exceeded approximately 1 mg/mL6,7,11–13 The formation of this phase depends on the polarity of the medium and the size of the GO flakes. Relaxation (~109 Hz), which arises from the rotation of the molecules around the long molecular axis, and the lower frequency relaxation (~107 Hz), which stems from the rotation around the short molecular axis[16,17]
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