Rheology of Lyotropic Nematogenic Nanorod Dispersions

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Davis0854010This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The objective of this research is to determine the rheological behavior of model lyotropic nanocylinder (e.g. nanorod, nanotube, nanowire) dispersions. Rheological characterization of lyotropic nanocylinder dispersions has only recently been made possible by improved, larger scale, synthesis techniques and increased understanding of dispersion thermodynamics. This research will determine 1) how effective rheology is at elucidating phase behavior, 2) the sensitivity of rheological characteristics to temperature above the percolation threshold, and 3) the effect of shear on microstructure. The primary model system investigated will be single-walled carbon nanotubes in aqueous DNA. This system was chosen because of the growing interest in using DNA to both disperse nanotubes and to produce multifunctional materials. In addition, inorganic nanocylinders in small molecule solvents will be investigated; inorganic nanocylinders have significant potential for use in electronic devices, solar panels, and sensors. The motivation for this research is threefold. First, understanding nanocylinder dispersion rheology and phase behavior is the next step in the ongoing evolution of liquid crystalline science. Based on well-established theories for the phase behavior of rods in solution, nanocylinder dispersions should form lyotropic liquid crystalline phases. However, nanocylinders with long lengths, high aspect ratios, significant rigidities, and attractive interactions make them significantly different than 'rod-like' polymers and other previously investigated systems. Second, protocols are needed for establishing the liquid crystallinity of nanocylinder dispersions. While the rheological signatures of lyotropic liquid crystalline polymer solutions are well known, it is not clear if nanocylinder dispersions will exhibit these same characteristics. Third, there is growing interest in the bottom-up assembly of nanorods into large-area aligned structures. Just as understanding the rheology and phase behavior of liquid crystalline polymers enabled advanced materials such as bullet proof vests, understanding the rheology and phase behavior of nanorod dispersions is likely to facilitate the development of processes for producing highly aligned macroscale structures from nanoscale building blocks. This research will also benefit the development of future scientists and engineers. The undergraduate and graduate student researchers participating in this research will gain experience that is applicable not only to nanotechnology, but also to the numerous fields that employ well-trained rheologists. Research findings will be incorporated into the PI's 'Macroscale Assembly of Nanomaterials' course which is available by streaming video. In addition, the PI will develop an outreach module for middle school students who attend Auburn's science and engineering camps and continue her efforts to facilitate diversity.