1. Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
2. Fiber and Polymer Science Program, North Carolina State University, Raleigh, North Carolina 27695, USA
3. Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA
4. Faculty of Physics, Adam Mickiewicz University, 61-614 Poznan, Poland
5. Department of Physics and Astronomy and Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada