NSTI Nanotech 2009

Phase Behavior and Processing of Inorganic Nanocylinder Dispersions

S. Murali, K. Pizarro, T. Xu, J. Boice, V.A. Davis
Auburn University, US

Keywords: silver nanorod, nanowire, liquid crystal, assembly, shear

Abstract:

Throughout its greater than 130 year history, liquid crystalline science has been an interdisciplinary field where new applications have been fueled by the development of new materials. The 1960ís syntheses of rod-like polymers fueled significant 1970ís and 1980ís research into their liquid crystalline phase behavior and response to the shear rates inherent in liquid phase processing. The resulting scientific understanding led to high performance materials such as DuPont Kevlar. Similarly, 1990ís nanocylinder syntheses motivate the need for understanding nanorod/nanowire liquid crystalline assembly and shear alignment. We report the liquid crystalline phase behavior of silver (Ag) nanorods. The rods have an average length of 6 microm and average diameter of 60 nm. The shear response of biphasic and liquid crystalline silver-ethylene glycol (Ag-EG) dispersions was found to be particularly intriguing. Low shear rates had little effect on defect annealing, intermediate shear rates resulted in uniform alignment, and high shear rates resulted in gap dependent multiplanar shear banding behaviors; the rods align in highly concentrated bands with low concentration regions between them. This behavior provides a potential new means to control nanorod placement and orientation in three dimensions by simply tuning the shear rates typically encountered in coating processes.
 
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