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Dissertation
Versatile Membranes Enabled by the Controlled Crystallization of Polymers from Carbon Nanotube Sidewalls
Doctor of Philosophy (Ph.D.), Drexel University
Dec 2013
DOI:
https://doi.org/10.17918/00001210
Abstract
Between top-down and bottom-up approaches to nanomanufacturing lies a technologically important length scale between ~10 - 100 nm that is difficult to access. One area where this dearth is noticed acutely is in membrane technology. The polymer electrolyte membrane fuel cell (PEMFC) is one area where such membranes could be of great service as gas diffusion layers, but this application further requires that the membrane must be electrically conductive. Materials that would be suitable for this purpose are extremely uncommon, and suitable materials that could be produced at large scales are virtually nonexistent. In 2005, our group demonstrated a novel carbon nanotube (CNT) functionalization technique. When polyethylene (PE) was mixed in dilute solution with dispersed CNTs and quenched to a controlled temperature, the former could take advantage of a favorable epitaxial relationship with the CNT sidewall. Thus, the controlled growth of polymer single crystal "kebabs" on CNT "shishes" could be imposed. Because the resulting structure resembled the classical PE "shish kebabs" first observed by Pennings after shear flow-induced crystallization, these structures were termed "nanohybrid shish kebabs" (NHSKs). It was recently determined that NHSKs could be collected in a nonwoven mat to produce "NHSK paper," which could be made free-standing. Basic structural features were studied and it was determined that these materials have pores in the mesoscale range. NHSK paper conductivity was found to be outstanding, in the range of a weak conductor. The ability to adjust wetting properties was noticed as another attractive property of this material: careful tuning of the polymer and CNT feed ratios can produce a superhydrophobic condition. Initiated chemical vapor deposition was used to coat polytetrafluoroethylene onto these materials, enhancing their hydrophobicity. This thesis represents the first comprehensive evaluation of NHSK paper's suitability for applications. In this work, morphological and structural features were explored. Methods to further functionalize NHSK paper were explored. Wetting behavior of NHSK paper was studied in detail. It was concluded that NHSK paper could become a transformative technology as gas diffusion layers in PEMFCs.
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Details
- Title
- Versatile Membranes Enabled by the Controlled Crystallization of Polymers from Carbon Nanotube Sidewalls
- Creators
- Eric Duncan Laird
- Contributors
- Christopher Y. Li (Advisor) - Drexel University, Materials Science and Engineering
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Materials Science and Engineering; College of Engineering; Drexel University
- Other Identifier
- 4377; 991018931815304721