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«ELECTRIC FIELD MANIPULATION OF POLYMER NANOCOMPOSITES: PROCESSING AND INVESTIGATION OF THEIR PHYSICAL CHARACTERISTICS A Dissertation by SUMANTH BANDA ...»

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ELECTRIC FIELD MANIPULATION OF POLYMER NANOCOMPOSITES:

PROCESSING AND INVESTIGATION OF THEIR PHYSICAL

CHARACTERISTICS

A Dissertation

by

SUMANTH BANDA

Submitted to the Office of Graduate Studies of

Texas A&M University

in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

December 2008 Major Subject: Materials Science & Engineering

ELECTRIC FIELD MANIPULATION OF POLYMER NANOCOMPOSITES:

PROCESSING AND INVESTIGATION OF THEIR PHYSICAL

CHARACTERISTICS

A Dissertation by

SUMANTH BANDA

Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Approved by:

Chair of Committee, Zoubeida Ounaies Committee Members, Dimitris Lagoudas Jim Boyd Hung-Jue Sue Jaime Grunlan Intercollegiate Faculty Chair, Tahir Cagin December 2008 Major Subject: Materials Science & Engineering iii ABSTRACT Electric Field Manipulation of Polymer Nanocomposites: Processing and Investigation of Their Physical Characteristics. (December 2008) Sumanth Banda, B.Tech, Jawaharlal Nehru Technological University;

M.S., Virginia Commonwealth University Chair of Advisory Committee: Dr. Zoubeida Ounaies Research in nanoparticle-reinforced composites is predicated by the promise for exceptional properties. However, to date the performance of nanocomposites has not reached its potential due to processing challenges such as inadequate dispersion and patterning of nanoparticles, and poor bonding and weak interfaces. The main objective of this dissertation is to improve the physical properties of polymer nanocomposites at low nanoparticle loading. The first step towards improving the physical properties is to achieve a good homogenous dispersion of carbon nanofibers (CNFs) and single wall carbon nanotubes (SWNTs) in the polymer matrix; the second step is to manipulate the well-dispersed CNFs and SWNTs in polymers by using an AC electric field.

Different techniques are explored to achieve homogenous dispersion of CNFs and SWNTs in three polymer matrices (epoxy, polyimide and acrylate) without detrimentally affecting the nanoparticle morphology. The three main factors that influence CNF and

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dispersion procedure is optimized for each polymer system, the study moves to the next step. Low concentrations of well dispersed CNFs and SWNTs are successfully manipulated by means of an AC electric field in acrylate and epoxy polymer solutions.

To monitor the change in microstructure, alignment is observed under an optical microscope, which identifies a two-step process: rotation of CNFs and SWNTs in the direction of electric field and chaining of CNFs and SWNTs. In the final step, the aligned microstructure is preserved by curing the polymer medium, either thermally (epoxy) or chemically (acrylate). The conductivity and dielectric constant in the parallel and perpendicular direction increased with increase in alignment frequency. The values in the parallel direction are greater than the values in the perpendicular direction and anisotropy in conductivity increased with increase in AC electric field frequency. There is an 11 orders magnitude increase in electrical conductivity of 0.1 wt% CNF-epoxy nanocomposite that is aligned at 100 V/mm and 1 kHz frequency for 90 minutes.

Electric field magnitude, frequency and time are tuned to improve and achieve desired

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I would like to acknowledge several people for their help in completing this dissertation.

First and foremost, I want to thank Zoubeida Ounaies, my doctoral advisor for the advice, guidance and support that she continuously provided to me throughout my graduate work. Her words of encouragement and careful reading of all my writing will never be forgotten. She is one of the rare advisors that students dream that they will find.

Without her support, I could not have done what I was able to do. I also extend my thanks to my doctoral committee, Dimitris Lagoudas, Jim Boyd, Hung-Jue Sue, and Jaime Grunlan, for their guidance and support throughout the course of this research.

My thanks to all my colleagues at Electroactive Materials Characterization Laboratory, especially Ricardo Perez, Sanjay Kalidindi, Sujay Deshmukh, Ainsley VanRooyen and Casey Whalen who helped me with my doctoral work. This work was supported in part by NSF-DMI and NASA URETI Texas Institute for Intelligent Bio-Nano Materials and Structures for Aerospace Vehicles (TIIMS).

Graduate life can be stressful and tiring sometimes, this would have not been possible without the support of all family members and friends. I would like to thank my parents, grandparents, sister, brother in law and friends for their encouragement and support.

Special thanks to my uncle Ramesh Chamala who encouraged me to pursue my doctoral

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DMAc N, N- dimethylacetamide βCN-APB Bi(3-amino phenoxy benzo nitrile) ODPA Oxydiphthalic anhydride UDMA Urethane dimethacrylate HDDMA 1, 6 Haxanediol dimethacrylate DEP Dielectrophoretic

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ε’ Dielectric constant σ’ Electrical conductivity ε0 Dielectric constant in vaccum εm Dielectric permittivity of medium εp Dielectric permittivity of particle

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Abstract

DEDICATION

ACKNOWLEDGEMENTS

NOMENCLATURE

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF TABLES

1. INTRODUCTION

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2.3.2 Theoretical analysis

2.4 Optical microscopy and scanning electron microscopy

2.5 Impedance spectroscopy

2.5.1 Electrical conductivity

2.5.2 Dielectric spectroscopy

2.5.3 In-situ electrical conductivity and dielectric constant................. 54

2.6 Raman spectroscopy

2.7 Dynamic mechanical analysis

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4. EFFECT OF ELECTRIC FIELD MAGNITUDE AND TIME ON

NANOPARTICLES IN POLYMERS

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5. PHYSICAL PROPERTIES OF ELECTRIC FIELD MANIPULATED

POLYMER NANOCOMPOSITES

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1.6 SEM micrographs of CNF-PP composites prepared by melt mixing.

(a) 15 wt% CNF and (b) 10 wt% CNF

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1.8 Functional groups are attached to (a) ends of SWNTs and (b) side wall of SWNTs

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1.10 TEM image of a crosssectional microtome of MWNT-PVA composite film

1.11 SEM micrographs of fracture surfaces (a) with surfactant and (b) without surfactant

1.12 SEM micrographs of fractures PAA with 1 wt% SWNTs. Aqueous mixtures with (a) pH of 2.9 and (b) pH of 9.2

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1.16 TEM images of aligned MWNTs. (a) Parallel and (b) perpendicular to the magnetic field direction

1.17 Optical microscopy images of gold nanoparticles between gold electrodes as a function of applied AC electric field frequency and amplitude. Gap between electrodes is 30 µm

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1.20 AFM image of SWNTs in between the electrodes, bridge the gap between electrodes.

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1.22 CNF network formation in PDMS using an DC electric field. OMs after (a) 0 min, (b) 1 min and (c) 10 min

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1.24 OMs of MWNTs network in epoxy composites by applying (a) DC electric field of 100 V/mm and (b) AC electric field of 100 V/mm at 1 kHz frequency.

1.25 SWNT network formation by the application of an AC electric field.

(a) Optical microscope and (b) SEM micrograph

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2.3 Silver paint is used as an electrode for aligned polymer nanocomposites.

Shaded region indicates the electrodes in the (a) parallel and (b) perpendicular directions..

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3.1 Flow chart showing various steps in solvent free processing of acrylate and epoxy polymer nanocomposites

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3.4 Flow chart showing various steps of solvent based processing of epoxy polymer nanocomposites

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3.7 OMs of CNF-epoxy polymer solutions (a) 1 wt% CNFs and (b) 3 wt% CNFs

3.8 Electrical conductivity of CNF-epoxy polymer nanocomposites as a function of frequency

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3.10 Dielectric constant of CNF-epoxy polymer nanocomposites as a function of frequency

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3.13 SEM micrograph of 0.5 wt% SWNT polyimide. (a) uniformly distributed SWNTs, scale bar is 2 mm, (b) SWNT wrapped with polymer matrix, scale bar is 200nm.

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3.15 Electrical conductivity of SWNT-polyimide nanocomposites as a function of different SWNT concentrations. Solid line is a trend line

3.16 Storage modulus of SWNT-polyimide nanocomposite as a function of temperature at different SWNT concentrations

3.17 Storage modulus of SWNT-polyimide nanocomposite as a function of SWNT concentration

4.1 Different stages of a CNF after the electric field is applied. Length of CNF is 25 µm. Applied voltage and time is (a) E=0, t=0 sec, (b) E=300 V/mm, t=2 sec and (c) E=300 V/mm, t=4 sec/ Arrow indicates direction of applied electric field

4.2 Rotation of an ellipsoidal SWNT bundle, arrow indicates direction of electric field. Magnitude of the applied electric field is 300 V/mm and the frequency is 10 Hz (a) t=0, (b) t=3 sec, and (c) t=5 sec. Scale bar is 20 µm.

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4.4 Raman spectra of SWNT-acrylate aligned at 300 V/mm, 1 kHz, 30 minutes. Raman spectra is obtained at different polarizer angles (0° to 90°).

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4.8 OM images of 0.03 wt% SWNT acryalte polymer solution. (a) E=0, (b) 100 V/mm, 30 minutes and (c) 100 V/mm, 25 kHz, 30 minutes. Scale bar in all the images is 100 µm.

4.9 Optical microscopy images of 0.03 wt% SWNT-acryalte system at an applied electric field of 300 V/mm, different frequencies (1 Hz to 25 MHz) and different time intervals (0-30 min)

4.10 OMS images of electric field manipulated 0.03 wt% SWNT-acrylate polymer solution. Applied electric field was 300 V/mm at 1 kHz frequency for a duration of (a) 6 hours, (b) 15 hours, (c) 45 hours, and (d) 62 hours.

4.11 In-situ electrical conductivity and dielectric constant of 0.03 wt% SWNT-acryalte solution (before cure) as a function of input measurement frequency 50 Hz to 1 MHz. The applied AC electric field magnitude is 300 V/mm and the frequency is 10 Hz, 100 Hz, 1 kHz, 10 kHz and 25 kHz. (a) electrical conductivity and (b) dielectric constant after 10 minutes of applying the electric field, (c) electrical conductivity and (d) dielectric constant after 30 minutes of applying the electric field.

4.12 (a) In-situ dielectric constant and (b) in-situ electrical conductivity of

0.03 wt% SWNT-acrylate solution (before cure) as a function of input measurement frequency. AC electric field magnitude is 300 V/mm and the frequency is 1 kHz

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4.14 (a) Electrical conductivity and (b) dielectric constant behavior of insulating and conducting polymer nanocomposites as a function of frequency.

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4.16 Distorted electric field lines due to the presence of particles

4.17 Clausius Mossoti factor of an ellipsoidal and spherical SWNT bundle in acrylate polymer as a function of frequency (10 Hz to 25 kHz).............. 103

5.1 Summary on the types of polymer nanocomposites along with their aligning electric field conditions and curing conditions

5.2 Electrical conductivity of electric field manipulated 0.03 wt% SWNTacrylate polymer nanocomposite asa function of frequency (a) parallel and (b) perpendicular to the electric field. Applied AC electric field was 300 V/mm, which was applied for 30 min

5.3 OM images of electric field manipulated SWNT-acrylate polymer nanocomposites. Applied electric field E = 300 V/mm, t = 30 minutes, frequency of (a) 100 Hz and (b) 1 kHz.

5.4 Electrical conductivity of electric field manipulated 0.1 wt% CNFepoxy polymer nanocomposite as a function of frequency (a) parallel and (b) perpendicular to the electric field. Applied AC electric field was 100 V/mm, which was applied for 90 min.

5.5 Electrical conductivity in the parallel and perpendicular direction of electric field manipulated 0.1 wt% CNF-epoxy polymer nanocomposite measured at 0.01 Hz. Electrical conductivity is plotted as a function of electric field frequency starting from 0.1 Hz to 1 kHz. Magnitude of the AC electric field was 100 V/mm, which was applied for 90 minutes....... 114

5.6 Electric field manipulated 0.1 wt% CNF-epoxy nanocomposite at 10 Hz electric field. (a) digital image and (b) OM at 10x magnification........ 115

5.7 Electric field manipulated 0.1 wt% CNF-epoxy nanocomposite at 1 kHz electric field. (a) digital image and (b) OM at 10x magnification............ 116

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5.9 Dielectric constant of electric field manipulated 0.1 wt% CNF-epoxy polymer nanocomposite as a function of frequency (a) parallel and (b) perpendicular to the electric field. Applied AC electric field was 100 V/mm, which was applied for 90 min



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