Materials Characterization in Polymer/CNT Fibers using Raman Spectroscopy

Lindsey Thomson

Advisor: Dr. Satish Kumar

Project Mentor: Bradley Newcomb

Conclusions

Acknowledgements I wish to thank Dr. Satish Kumar for accepting me onto his

research team and his support as my faculty advisor, and Dr.

Fred Cook for his advice and encouragement during my

undergraduate research. Special thanks to Brad Newcomb for

his guidance, patience, and assistance as my project mentor.

Introduction Resonance Raman Spectroscopy (RRS) was used

to determine CNT chiralities of single-walled

(SWNT) and few-walled carbon nanotubes (FWNT).

An incident laser (λ = 785 nm, E = 1.58 eV) was

used, which allowed for the determination of SWNT

and FWNT chiralities in CNT powders and

PVA/SWNT, PAN/SWNT, and PAN,FWNT gel spun

composite fibers. Frequency shifts of the ωrbm peak

positions and intensity shifts were observed after

preparing the composite polymer/CNT fibers. ωrbm

frequency shifts were attributed to the surrounding

polymeric material (environmental effect), while

intensity shifts (up or down) are attributed to

differences in the bundling state of the CNTs within

the polymeric/CNT fibers as compared to the as-

received CNT. Stress transfer by single filament

straining of polyacrylonitrile/ carbon nanotube

(PAN/CNT) and polyvinyl alcohol/carbon nanotube

(PVA/CNT) fibers was observed by monitoring G

mode downshifts as a function of fiber strain.

Changes in energy band gap also occur, allowing

for the precise determination of SWNT chiralites.

Bundling Effects in Polymer/CNT Fibers

5 nm

GT PAN CF

𝛥𝐸𝑔𝑎𝑝 = 𝑠𝑔𝑛 2𝑛 + 𝑝 3𝑡𝑜 [ 1 + 𝑣 σ cos 3𝜃 + 𝛾 sin 3𝜃 ]

Best fit line

• Type of polymer and type of CNT effect the

environmental coefficient

• Same chiralities are present in the fiber as in the

powder, but with an upshift in peak position

• Bundling changes the electronic transition energy

of CNTs

Table of Peak Position, Chiralities, and Diameter

Straining Effects in Polymer/CNT

Fibers

• High intensity peaks have ΔE value approaching 0

• ΔE is the difference between laser’s energy and ECNT

• High intensity in (10,2) peak represents a bundled state

• ΔE moves farther off resonance from laser when the (10,2)

peak is debundled

• Debundled CNTs can improve mechanical and electrical

properties of polymer/CNT composites

• Vertical shift due to bundling effect

• Horizontal shift due to environmental effect

Raman Spectroscopy

O'Connell, M. J.; Sivaram, S.; Doorn, S. K., Near-infrared resonance Raman excitation profile studies of single-walled carbon nanotube

intertube interactions: A direct comparison of bundled and individually dispersed HiPco nanotubes. Physical Review B 2004, 69 (23).

• Horizontal shifts of G mode due to straining along

axial direction

• G peak shifts left because stretching/straining

weakens the C-C bond

• Shift in G peak shows that the CNT within the fiber

is being strained, not just polymer sliding past the

CNT as the fiber is strained

Future Work/ Application • Industry: use Raman to monitor bundling behavior

of CNTs on a systems line

• Control over changes in energy band gap for use

in tunable electronic devices