EFFECTS OF NANOPARTICLE AND MATRIX INTERFACE ON NANOCOMPOSITE PROPERTIES A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Sandi G. Miller August, 2008 EFFECTS OF NANOPARTICLE AND MATRIX INTERFACE ON NANOCOMPOSITE PROPERTIES Sandi G. Miller Dissertation Approved: Accepted: Advisor Department Chair Dr. Darrell H. Reneker Dr. Mark D. Foster Committee Member Dean of the College Dr. Ali Dhinojwala Dr. Stephen Z.D. Cheng Committee Member Dean of the Graduate School Dr. Gary R. Hamed Dr. George R. Newkome Committee Member Date Dr. Michael A. Meador Committee Member Dr. Sadhan C. Jana ii ABSTRACT The objectives of this work were to functionalize two nanoparticles, layered silicate clay and expanded graphite, and evaluate the effects of surface modification on polymer nanocomposite properties. Two thermosetting resin systems were evaluated, a polyimide for high temperature applications, and a general use epoxy. The chemistry of the modifier or the particle surface was tailored in each case to optimize nanocomposite properties such as: particle dispersion, thermal oxidative stability (TOS), electrical conductivity, strength, and toughness. Dispersion of layered silicate clay into the two separate matrices demonstrated an apparent affinity between the silicate surface and aromatic compounds. Steps were taken in each case to disrupt that attraction; resulting in improved material properties. The dispersion of layered silicate clays into a thermosetting polyimide demonstrated that improved thermal oxidative stability was achieved only when the clay was modified with a combination of an aromatic diamine and an alkyl ammonium ion. When such a system was employed, the nanocomposite TOS improved by 25% over that of the base polyimide. Attention to the interactions between clay and aromatic containing compounds was also necessary for silicate modification and dispersion in an epoxy blend. Here, preferential contact between the clay and the aromatic containing sections of the blend was observed; resulting in nanocomposites exhibiting little enhancement to epoxy properties. By forcing the clay into the non-aromatic component, the material yield stress iii increased by up to 65%, Young’s modulus increased by up to 80%, and increases in Tg of up to 11oC were observed relative to the base resin. Within nano-graphite containing materials, trade-offs in functionalization, dispersion, and properties were evaluated. Functionalization of graphite proved beneficial in terms of dispersion. For example, an epoxy functionalized graphite nanoparticle resulted in acceptable dispersion throughout the matrix, with a minimal level disruption of the sp2 hybridization within the graphene sheet. As a result, the nanocomposite structure increased yield stress by 30% at a filler loading of 0.67 vol%. Electrical conductivity increased by 5 orders of magnitude at this same loading. Graphite materials that did not disperse well, or were more heavily oxidized exhibited conductivity as loading increased to 1.5 vol%. In the poorly dispersed expanded graphite material, a 35% increase in yield stress was observed, but with significant reduction in ductility. With the heavily oxidized graphene sheets, 50% increase in yield stress was observed, following adjustments to the resin stoichometry. iv ACKNOWLEDGEMENTS First and foremost, I wish to thank Dr. Michael Meador for the guidance, encouragement, kindness, and support that he provided as a mentor. I would also to sincerely thank Professor Darrell Reneker for taking the time to work with me through the later stages of my graduate career at the University of Akron. I would also like to extend that gratitude to all my committee members, including Professor Ali Dhinojwala, Professor Gary Hamed, and Professor Sadhan Jana. I sincerely appreciate their time, effort, and critical evaluation of my work. This research for this project was conducted at the NASA Glenn Research Center. As such, there are a number of people who have helped me over the years. The entire Polymers Branch, both past and present, has been an incredible source of knowledge and guidance. In particular, I would like to thank Daniel Scheiman, Linda Inghram, Linda McCorkle, Gary Roberts, Justin Littell, Lee Kohlman, and Paula Heimann. Additionally, I would like to acknowledge the many researchers outside of the Polymers Branch who have been invaluable resources for assistance with material characterization. Specifically, Dave Hull, Joy Buelher, Joe Lavelle, Dorothy Lukco, Rick Rogers, Bob Mattingly, and Anna Palczer. I would also like to thank the friends who have encouraged me over the many, many years it has taken to complete this degree, and my parents and brother for their un-ending v support. Finally, I would not have been able to complete this work without the patience, love, and support I received from my husband Kyle and daughters, Kennedy and Ashley. vi TABLE OF CONTENTS Page LIST OF TABLES…………………………………………………………………….…xii LIST OF FIGURES……………………………………………………………………..xiv CHAPTER I. INTRODUCTION…………………………………………………………………….1 1.1 Polymer Nanocomposites…………………………………………………6 1.2 Layered Silicate Clay Nanocomposites…………………………………...8 1.2.1 High Temperature Polyimide Matrix……………………………...8 1.2.2 Epoxy Blend Matrix……………………………………………….9 1.3 Graphite Nanocomposites………………………………………………..10 1.3.1 Epoxy Blend Matrix……………………………………………...10 II. OBJECTIVES………………………………………………………………………..12 2.1 PMR-15 Matrix Nanocomposites………………………………………..12 2.2 Epoxy Resin Matrix Nanocomposites…………………………………...14 2.3 Summary…………………………………………………………………15 III. BACKGROUND……………………………………………………………………17 3.1 Conventional Fillers……………………………………………………...17 3.2 Comparison of Conventional and Nano Fillers………………………….18 vii 3.3 Layered Silicate Clays…………………………………………………...23 3.4 Organic Modification of Layered Silicate Clays………………………...25 3.5 Dispersion of Layered Silicate Clays…………………………………….30 3.6 Dispersion Mechanism…………………………………………………...35 3.7 Polymer-Clay Interface…………………………………………………..38 3.8 Nanocomposite Properties……………………………………………….39 3.9 Summary of Layered Silicate Clay Nanocomposites……………………40 3.10 Expanded Graphite……………………………………………………….41 3.11 Dispersion of Expanded Graphite………………………………………..45 3.12 Dispersion Techniques…………………………………………………...46 3.13 Polymer-Graphite Interface……………………………………………...48 3.14 Nanocomposite Properties……………………………………………….49 3.15 Conclusion of Expanded Graphite Nanocomposites…………………….52 3.16 Summary…………………………………………………………………52 IV. EFFECTS OF SILICATE-MODIFIER ORIENTATION ON NANOCOMPOSITE INTERFACE AND PROPERTIES IN A HIGH TEMPERATURE POLYIMIDE MATRIX…………………………………………………………………………….53 4.1 Introduction………………………………………………………………53 4.2 Experimental Details……………………………………………………..56 4.2.1 Materials…………………………………………………………56 4.2.2 Synthetic Procedures……………………………………………..57 4.2.3 Nanocomposite Synthesis………………………………………..57 4.2.4 Characterization………………………………………………….59 4.3 Results and Discussion…………………………………………………..61 viii 4.3.1 Ion Exchanged Clays…………………………………………….61 4.3.2 Orientation Characterization by Infrared Spectroscopy…………66 4.3.3 Characterization of Silicate Dispersion in PMR-15……………...68 4.3.4 Processing PMR-15 Nanocomposites……………………………71 4.3.5 Thermal Stability of PMR-15 Nanocomposites………………….76 4.3.6 Polymer Matrix Composites……………………………………..82 4.4 Conclusions………………………………………………………………86 V. EFFECT OF INTERFACE ON SILICATE DISPERSION IN A CO-EPOXY SYSTEM………………………………………………………………………….…89 5.1 Background………………………………………………………………89 5.2 Introduction………………………………………………………………90 5.3 Experimental……………………………………………………………..92 5.3.1 Materials…………………………………………………………93 5.3.2 Nanocomposite Preparation……………………………………...93 5.3.3 Characterization………………………………………………….95 5.4 Results……………………………………………………………………96 5.4.1 Characterization of Silicate Dispersion………………………….96 5.4.2 Interaction Between Cloisite 30B and Aromatic or Aliphatic Compounds………………………………………………………99 5.4.3 Glass Transition Temperature…………………………..………103 5.4.4 Tensile Tests…………………………………………………....105 5.4.4.1 General Trends Observed From Tensile Testing…….…111 5.4.4.2 Relation of Matrix Mobility…………………………….111 5.4.5 Permeability…………………………………………………….115 ix 5.4.6 Coefficient of Thermal Expansion……………………………...115 5.5 Discussion………………………………………………………………117 5.5.1 Microstructure…………………………………………………..117 5.5.2 Preferential Interaction Between Silicate Clay and Aromatic Compounds……………………………………………………..121 5.5.3 Pre-Swelling Clay with the Aliphatic Component……………...121 5.5.4 Interpretation of Results………………………………………...122 5.5.4.1 Glass Transition Temperature…………………………..122 5.5.4.2 Mechanical Properties…………………………………..123 5.6 Conclusions……………………………………………………………..123 VI. FUNCTIONALIZED GRAPHITE NANOCOMPOSITES……………………….125 6.1 Background……………………………………………………………..125 6.2 Introduction……………………………………………………………..125 6.3 Experimental……………………………………………………………127 6.3.1 Materials………………………………………………………..127 6.3.2 ATI Preparation………………………………………………...127 6.3.3 Nanocomposite Preparation………………………………….…128 6.3.4 Organic Modification of Graphite……………………………...128 6.3.5 Characterization………………………………………………...129 6.4 Results…………………………………………………………………..130 6.4.1 Characterization of Graphite Materials…………………………130 6.4.1.1 Expanded Graphite Characterization…………………...132 6.4.1.2 Characterization of Adherent Technologies Graphite.…135 x 6.4.1.3 Characterization of Exfoliated Graphite (FGS)………...140 6.4.2 TGA Determination of Graphite Functionalization…………….143 6.4.3 Dispersion in an Epoxy Matrix…………………………………146