Carbon nanotubes exhibit remarkable physical properties and
there is considerable interest in using them as nanoscale building
blocks for a new generation of novel materials and applications.
Despite this promise, fundamental issues related to the dispersion,
fractionation, orientation, and manipulation of individual nanotubes
remain unresolved and efficient bulk processing schemes do not
yet exist. In light of these issues, establishing routes to
proficient processing will depend in part on a detailed
understanding of the response of carbon nanotube suspensions
and melts to changes in such parameters as composition, temperature,
aspect ratio, and shear stress.
Experimental Approach
Quantifying Structure, Dispersion, and Orientation with:
Rheo-optics - Light scattering, and Microscopy
Rheology – Controlled Strain and Controlled Stress
Flow Birefringence and Dichroism
Small-angle Neutron Scattering
Complete Processing Phase Diagram – Confinement, Shear Rate, and Composition
Confocal Scanning and Fluorescence Microscopy
Digital Image Analysis
Results
We
report elastic instabilities associated with flow-induced clustering
in semi-dilute non-Brownian colloidal nanotubes. Rheological
and optical measurements are compared with simulations of mechanical
flocculation in sheared fiber suspensions, and the evolving
structure is characterized as a function of confinement and
shear stress. We also use a variety of methods to measure the
anisotropy of sheared carbon nanotube suspensions over the entire
semi-dilute regime. Our measurementshighlight the importance
of hydrodynamic excluded-volumeinteractions, with scaling over
a broad range of reduced strainrate, or Peclet number. Our results
also suggest howthese interactions might be exploited to fractionate
carbon nanotubes by length in simple shearing flows.
Recent Press
Negative normal stress, Physics News Updates (American Institute
of Physics), Physics Today 57, 9 (2004).
Negative normal stress, Physics News Updates (American Institute
of Physics), 674, February 23, 2004.
Mixing up nanotubes causes complications, Nanotechnology News
(Institute of Physics), February 2004 (www.nanotechweb.org).
Mixing carbon nanotubes with polymers, Small Times (Small Times
Media), March/April 2004 (www.smalltimes.com).
Stirring Research Provides Recipe for Nanotube Success, NIST
Tech Beat (NIST), January 30, 2004.
Recent Publications
Anisotropy of sheared carbon nanotube suspensions, D. Fry,
B. Langhorst, H. Kim, E. A. Grulke, H. Wang, and E. K. Hobbie
(preprint, to be submitted to Physical Review Letters).
Small-angle neutron scattering study of dispersing single-walled
carbon nanotubes with surfactants, H. Wang, W. Zhou, D. L. Ho,
K. I. Winey, J. E. Fischer, C. Glinka, and E. K. Hobbie (submitted
to Nano Letters).
Optical anisotropy of nanotube suspensions, E. K. Hobbie, Journal
of Chemical Physics 121, 1029 (2004) [also Virtual Journal of
Nanoscale Science and Technology 10(1), 31 (2004)].
Elastic flow instability in nanotube suspensions, S. Lin-Gibson,
J. A. Pathak, H. Wang, E. A. Grulke, and E. K. Hobbie, Physical
Review Letters 92, 048302 (2004) [also Virtual Journal of Nanoscale
Science and Technology 9(5), 8 (2004)].
Amphiphobic carbon nanotubes as macroemulsion surfactant, H.
Wang and E. K. Hobbie, Langmuir 19, 3092 (2003).
Orientation of carbon nanotubes in a sheared polymer melt, E.
K. Hobbie, H. Wang, H. Kim, S. Lin-Gibson, and E. A. Grulke,
Physics of Fluids 15, 1196 (2003) [also Virtual Journal of Nanoscale
Science and Technology 7(15), 45 (2003)].
Optical measurements of structure and orientation in sheared
carbon-nanotube suspensions, E. K. Hobbie, H. Wang, H. Kim,
C. Han, E. Grulke, and J. Obrzut, Review of Scientific Instruments
74, 1244 (2003) [also Virtual Journal of Nanoscale Science and
Technology 7(11), 46 (2003)].
Contributors:
D. Fry, S. Lin-Gibson, J. Patak, H. Wang, E. K. Hobbie
Processing Characterization Group
Polymers Division
Materials Science and Engineering Laboratory
