Shear-Induced Anisotropy of Concentrated Multi-walled Carbon Nanotube Suspensions Using X-ray Scattering

X-ray scattering is used to measure particle orientation in concentrated multiwalled carbon nanotube (MWNT) suspensions under shear flow. MWNTs were dispersed in a Newtonian suspending fluid (uncured epoxy). The dispersions exhibit shear thinning, approaching the matrix viscosity at high shear rates...

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Bibliographic Details
Published inJournal of rheology (New York : 1978) Vol. 55; no. 5
Main Authors Pujari, Saswati, Rahatekar, Sameer, Gilman, Jeffrey W., Koziol, Krzysztof K., Windle, Alan H., Burghardt, Wesley R.
Format Journal Article
LanguageEnglish
Published United States 07.02.2012
Subjects
ANISOTROPY
ASPECT RATIO
BREAKDOWN
CARBON
NANOSCIENCE AND NANOTECHNOLOGY
NANOTUBES
ORIENTATION
SCATTERING
SHEAR
STORAGE
TRANSIENTS
VISCOSITY
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Summary:X-ray scattering is used to measure particle orientation in concentrated multiwalled carbon nanotube (MWNT) suspensions under shear flow. MWNTs were dispersed in a Newtonian suspending fluid (uncured epoxy). The dispersions exhibit shear thinning, approaching the matrix viscosity at high shear rates. This is accompanied by progressive development of MWNT orientation along the flow direction with increasing shear rate. The impact of MWNT aspect ratio and concentration on steady-state orientation is explored. In one sample (2 wt. % dispersion of short MWNTs), orientation was measured in both the flow-gradient (1-2) and flow-vorticity (1-3) planes of shear flow to provide a more complete picture of the three-dimensional orientation state. Also in this sample, 1-3 plane measurements were conducted using both small- and wide-angle x-ray scattering (SAXS and WAXS). While the two methods produce qualitatively similar results, WAXS-derived measures of flow-induced anisotropy are consistently larger than SAXS data. In transient measurements following step-down in shear rate, MWNT orientation is found to decrease on similar time scales as viscosity increases. Prolonged growth of storage modulus is observed following flow cessation, accompanied by an unexpectedly rapid partial loss of MWNT orientation. The rheological and orientation data are discussed in terms of distortion, breakdown, and reformation of percolated MWNT networks in these samples.
Bibliography:National Science Foundation (NSF)
ISSN:0148-6055
1520-8516
DOI:10.1122/1.3609854