Discipline: Technology and Engineering
Subcategory: Materials Science
Kyrstyn Ong - Swarthmore College
Co-Author(s): Catherine Kanimozhi, University of Wisconsin-Madison, WI
Semiconducting single-walled carbon nanotubes (s-SWCNTs) are seamless cylinders of carbon atoms packed into a honeycomb lattice that have the potential to revolutionize nanoelectronics due to their high conductivity. However, the propensity for raw semiconducting nanotubes to conglomerate with undesirable metallic nanotubes (m-SWCNTs) makes the widespread application of s-SWCNTs in field effect transistors difficult. It is therefore essential to be able to disperse these nanotubes while maintaining their excellent electronic properties. Although there are many methods of nanotube dispersion, wrapping with conjugated polymers has demonstrated a particularly exceptional ability to disperse and to preserve the conductivity of s-SWCNTs through noncovalent interaction with the sp2 hybridized surface. However, it is not well understood why certain conjugated polymers, such as those that are fluorene based, are much better dispersants than other polymers. To that end, we synthesized different molecular weights of poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt-co-(6,6-(2,2-bipyridine))] (PFO-BPy) via a Suzuki coupling carbon-carbon reaction in order to test the effect that changing the molecular weight has on the thermal properties of the polymer and to determine whether or not this synthetic method yields comparable results to commercial methods. We polymerized PFO-BPy with commercially obtained monomers in DMF under nitrogen atmosphere for forty-eight hours and determined that our product was relatively pure from NMR spectra. This indicates that the Suzuki coupling reaction is a valid method of PFO-BPy synthesis. The 378°C decomposition temperature and 37% weight loss of our synthesized polymers are consistent with the 382°C decomposition temperature and 40% weight loss associated with commercial polymers. The decomposition temperature and weight loss do not vary greatly due to molecular weight. Therefore, these findings suggest that the thermal properties of PFO-BPy are not dependent on molecular weight. After adding our polymer to full length HiPco carbon nanotubes, we observed that a relatively low molecular weight fraction of PFO-BPy successfully dispersed the nanotubes after sonification and before purification. Further studies include purifying the dispersion mixture in order to determine the specificities of low molecular weight polymer selection and determining whether the selective sorting strength of the conjugated polymer is affected by molecular weight.
References: Li, Z., Liu, Z., Sun, H., & Gao, C. (2015). Superstructured Assembly of Nanocarbons: Fullernes, Nanotubes, and Graphene. Chem. Rev., 115(5), 7046-7117. doi: 10.1021/acs.chemrev.5b00102
Lemasson, F., Berton, N., Tittmann, J., Hennrich, F., Kappes, M. M., & Mayor, M. (2012). Polymer Library Comprising Fluorene and Carbazole Homo- and Copolymers for Selective Single-Walled Carbon Nanotubes Extraction. Macromolecules, 45(2), 713-722. doi: 10.1021/ ma201890g
Funder Acknowledgement(s): This study was funded by NSF EFRI (EFRI-1240268). This study was also funded by the National Science Foundation (DMR-1507409).
Faculty Advisor: Padma Gopalan, firstname.lastname@example.org
Role: I performed all the synthetic experiments and gathered and analyzed the data with guidance from my mentor Catherine Kanimozhi, a postdoctoral research fellow. My mentor operated the differential scanning calorimeter and the thermal gravimetric analysis apparatus since undergraduate students are not allowed to use these devices.