THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Wednesday, December 4, 2019

11:00 AM
in MRDC 3515

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Mohammad Hamza Kirmani

"Studies on High-Performance Thermosets and Tailoring of their Interface and Interphase with Carbon-Nanotubes for Applications in Deep Space Exploration Vehicles"

Committee Members:

Prof. Satish Kumar, Advisor, MSE

Prof. Karl Jacob, MSE

Prof. Kyriaki Kalaitzidou, ME

Prof. Naresh Thadani, MSE

Prof. Seung Soon Jang, MSE

Abstract:

One of the many challenges involved in human travel to mars is the lack of materials that fulfill the requirement for these missions. NASA calls for advanced materials with a quasi-specific tensile strength and modulus of 3 and 150 GPa/g/cc, respectively, and an interlaminar fracture toughness of 0.3 N/mm, that is, a two-three fold improvement in properties compared to the current state of the art (SOA) carbon fiber reinforced plastics (CFRP). Polymer- carbon nanotube (polymer- CNT) composites are expected to have significantly better mechanical properties than those of the current SOA CFRP and thus qualify as potential candidate for achieving the target mechanical properties in materials required for the mars mission. CNT containing polymer composites, however, have some limitations, one of which is the load transfer at the CNT- polymer interface. The interface plays a critical role in determining the overall macroscale properties of the composite. While, significant attention has been directed to this end, the CNTs in the composites have not yet reached their full potential.   

This thesis aims at investigating three of the many aspects that could potentially have substantial effects on the polymer-CNT interface. First, from a CNT stand-point, CNTs may contain amorphous carbon, among other impurities which consequently could interfere with the interfacial interactions of the CNT and the polymer. While such impurities are expected to have a negative effect on the polymer-CNT interface, quantitative evidence of the extent of such effects is lacking. To this end, for this thesis, studies on the difference in interfacial straining have been conducted on composites of polyurea with two types of CNT sheets: (a) sheets containing amorphous carbon and (b) sheets that were thermally treated to remove amorphous carbon. 

Second, from a polymer standpoint, high performance aerospace grade resin such as bismaleimide (BMI) can have multiple components. Studies in the literature have reported, geometry and arrangement of constituent building blocks in a material to be extremely critical to its overall toughness at the macro scale. E.g., nacre has a work of fracture ~3000 times higher than its building block (monolithic calcium carbonate). It is thus of interest to investigate the effect of processing on the molecular arrangement in a heterogeneous BMI, both, with and without CNTs. BMIs also are inherently brittle and improvement in their fracture toughness is desirable. To this end, for this thesis, studies have been conducted using a multi component BMI which was processed under (a) melt and cast (referred to as Melt) approach and (b) a dual asymmetric centrifuge based high speed shear mixing (referred to as HSSM) approach to enforce molecular rearrangement.  

Third, sizing has proven to be successful in enhancing interfacial interactions between the carbon fiber and polymers in CFRPs, however, there is no literature report to date on the use of a carbon fiber sizing in a polymer -CNT system. Given, that now continuous forms of CNT macro assemblies such as CNT yarns are commercially available, there is potential to surface treat and size CNT yarns on a continuous basis, similar to the treatment process for carbon fibers for making composites. It is hence of interest to explore the effect of sizing of CNTs on the interfacial interactions with polymers. To this end, for this thesis, three types of interfaces between the carbon nanotubes and the BMI are being studied. These are (a) pristine CNT-BMI, (b) functionalized CNT- BMI and (c) sized f-CNT BMI. 

Finally, preliminary work on tailoring the interface of the CNTs with polymer has led to the observation of an unprecedented, visible range photoluminescence emission. Studies in the literature, report bandgap luminescence emission only in single wall carbon nanotubes (SWNT) and in the near-infrared range. The CNTs used in the preliminary work are multiwall (MWCNT) and the emission observed is in the visible region. MWCNT cannot fluoresce on their own. There is also no literature report on the visible range photoluminescence emission in either SWNT or MWCNT based polymer composites. The formation of electron acceptor donor complexes in some polymer-CNT composite may provide some guidance to start understanding of this unique phenomenon. A better understanding of this phenomenon should provide new insights into CNT polymer interactions that can have important implications for structural, opto-electronic as well as in applications beyond what could be envisioned at this time.