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, August 3, 2016

1:00 PM
in MRDC 3515

will be held the

DISSERTATION DEFENSE

for

Amir Bakhtiary Davijani

“Effect of Poly(methyl methacrylate) Wrapping on the Structure and Properties of CNT Films, and Polymer/CNT Films and Fibers”

Committee Members:

Prof. Satish Kumar, Advisor, MSE
Prof. Karl Jacob, MSE
Prof. Hamid Garmestani, MSE
Prof. Donggang Yao, MSE
Prof. Seung Woo Lee, ME

Abstract:

Carbon nanotubes (CNTs) exhibit high electrical and thermal conductivity and good mechanical properties, making them suitable fillers for composites. Their effectiveness as a filler is affected by their state of aggregation. Various solvents, surfactants, and processing techniques have been studied to improve CNT dispersion in polymers. However, prior to this work there is no suitable solution for achieving good CNT dispersion. In this study, a novel process has been developed that prevents CNT aggregation. Ordered helical wrapping of poly (methyl methacrylate) (PMMA) has been achieved on single wall carbon nanotubes (SWNTs). PMMA wrapped SWNT dispersions in dimethylformamide (DMF) are found to be stable for over three months at room temperature. Ordered PMMA wrapping has been confirmed by X-ray diffraction, and the wrapping behavior has also been verified using molecular modeling. PMMA only wraps on SWNTs with diameter of ~1 nm and not on larger diameter CNTs, such as few wall and multi wall carbon nanotubes. PMMA wrapped SWNT dispersions have also been characterized using UV-vis and Raman spectroscopy which confirm exfoliation of PMMA wrapped SWNTs.

The novel finding has been successfully leveraged for electrical energy storage and mechanical reinforcement. SWNT buckypapers, typically have a surface area of about 650 m2/g. Using PMMA wrapping, SWNT buckypapers with surface area as high as 950 m2/g have been processed. These buckypapers exhibited significantly higher energy storage performance when used as electrodes in electrochemical supercapacitor. At a given power density, the energy density of the high surface electrodes was more than four times higher than the best value reported in the literature to-date for carbon nanotube or graphene electrodes.

Wrapping SWNTs with PMMA in buckypaper increased the modulus and tensile strength 5.9 and 3.7 times, respectively, compared to pristine SWNT buckypaper. Stress transfer studies on buckypapers revealed that while non-wrapped SWNTs experienced negligible stress during deformation, PMMA wrapped SWNTs took up to ~1 GPa stress before mechanical failure of the buckypaper. The modulus of composite films with PMMA wrapped SWNTs was 75 % higher than non-wrapped SWNT films. The effect of PMMA wrapping on thermomechanical properties and electrical conductivity of composite films is also reported.

PMMA wrapped and non-wrapped SWNTs were incorporated in PAN fibers and the effect of PMMA wrapping on mechanical properties, and stress transfer was characterized. The stress transfer analysis of SWNTs in precursor fiber indicated 45 % higher interfacial shear strength in PMMA wrapped SWNTs compared to non-wrapped SWNTs. PMMA wrapping effectively debundled SWNTs in the PAN fibers as evidenced by Raman spectroscopy of the precursor fiber. SEM images of the carbon fiber fracture surface revealed 60% reduction in fibril size when PMMA wrapped SWNTs were used instead of non-wrapped SWNTs.