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Monitoring of Glass Transition at a Polymer MONITORING OF GLASS TRANSITION AT A POLYMER SURFACE BY LOCALIZED SURFACE PLASMON RESONANCE By RATAN KISHORE PUTLA Bachelor of Technology in Mechanical Engineering Jawaharlal Nehru Technological University Hyderabad, India 2006 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE December, 2010 MONITORING OF GLASS TRANSITION AT A POLYMER SURFACE BY LOCALIZED SURFACE PLASMON RESONANCE Thesis Approved: Dr. A. Kaan Kalkan Assistant Professor of Mechanical and Aerospace Engineering Thesis Adviser Dr. Sandip P. Harimkar Assi stan t Professor of Mechanical and Aerospace Engineering Committee Member Dr. Ranji Vaidyanathan Herrington Professor of Advanced Materials Committee Member Dr. Mark E. Payton Dean of the Graduate College ii ACKNOWLEDGMENTS I am very thankful to my adviser Dr. A. Kaan Kalkan for offering me a very exciting project and guiding me through it with valuable inputs in the form of teaching, explaining and directing in the concepts that form the backbone for my research. I am also thankful to Dr. Hongbing Lu, Dr. Sandip P. Harimkar and Dr. Ranji Vaidyanathan for their valuable time spent in giving me their invaluable suggestions and feedback. I also thank Dr. A. Lloyd Bumm of Physics and Astronomy Department, University of Oklahoma for helping me with valuable inputs in advanced spectroscopy. I am also pleased to acknowledge all my colleagues of the Functional Nanomaterials Laboratory for their support and encouragement. I would also like to acknowledge NASA, NSF, TBag and Ocast for supporting my research work. I take this opportunity to thank my beloved dad & mom, uncle & aunt, sisters and brother-in-law for their prayers, moral support and great encouragement. Above all, I sincerely thank, owe and dedicate this research work to my beloved FATHER JESUS without WHOSE help I would never been able to reach this level in my life. I thank HIM for HIS constant encouragement, moral support and being my driving force throughout this research work. iv TABLE OF CONTENTS Acknowledgements....................................................................iv Table of contents...................................................................... v List of tables........................................................................... vi List of figures..........................................................................vii 1. Introduction ........................................................................ 1 2. Literature review and background .............................................. 7 3. Theoretical model ............................................................... 15 4. Experimental procedure ......................................................... 22 4.1 Sample preparation ......................................................... 22 4.2 Optical measurements ...................................................... 23 4.2.1 Extinction and transmission ........................................ 23 4.2.2 Temperature control ................................................ 26 4.2.3 Spectral measurements ............................................. 30 5. Results and discussion ............................................................ 32 5.1 Temperature series spectra................................................ 32 5.2 Time series spectra.......................................................... 37 5.3 Calculating the normalized penetration depth (X) from the time series LSPR optical extinction spectra....................................50 5.4 Calculating the average penetration depth from the time series LSPR optical extinction spectra........................................... 52 5.5 Driving force behind the embedding of a nanoparticle into the polymer surface..............................................................55 6. Conclusions and future work .................................................... 56 References.............................................................................60 v LIST OF TABLES Table Page I. Various techniques implemented in probing the Tgs of polymers by embedding nanoparticles ..................................................... 9 vi LIST OF FIGURES Figure Page 3.1 Schematics illustrating the sinking of a nanoparticle in a polymer......19 4.1 Illustration of the custom-made temperature control system........... 28 4.2 Schematic illustrating the temperature-controlled optical cell..........28 4.3 Photograph of the heating coil-wound-glass tube employed in the temperature-control system...................................................29 5.1 Temperature series optical extinction spectra of gold nanoparticles deposited on PiBMA..............................................................33 5.2 Smoothened data of temperature series spectra of gold nanoparticles deposited on PiBMA .............................................................34 5.3 Optical extinction peak (wavelength) versus temperature of gold nanoparticles deposited on PiBMA............................................35 5.4 Time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 55 °C...................................................38 5.5 Original (top) and smoothened (below) time series extinction spectra of nanoparticles deposited on PiBMA at 55 °C during the first 20 minutes...........................................................................39 vii 5.6 Peak shift in time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 55 °C................................40 5.7 Time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 60 °C.................................................41 5.8 Smoothened time series extinction spectra of gold nanoparticles deposited on PiBMA at 60 °C ................................................ 42 5.9 Peak shift in time series LSPR optical extinction spectra of gold nanoparticles on PiBMA at 60 °C............................................ 42 5.10 Time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 65 °C..................................................43 5.11 Smoothened time series extinction spectra of gold nanoparticles deposited on PiBMA at 65 °C..................................................44 5.12 Peak shift in time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 65 °C.................... ............44 5.13 Time series LSPR optical extinction spectra of gold nanoparticles deposited on PiBMA at 45°C...................................................45 5.14 Time series extinction spectra of gold nanoparticles on PiBMA at 45 °C after Savitzky-Golay smoothening....................................46 5.15 Extinction peak wavelength as a function of time at 45°C ............. 46 5.16 Peak shifts in time series LSPR optical extinction of gold nanoparticles deposited on PiBMA at 45, 55, 60 and 65 °C ...............................49 5.17 Average normalized penetration depth ʹ for the surrounding medium of gold nanoparticles as they embed into PiBMA at 45, 55, 60 and viii 65ºC...............................................................................51 5.18 Rate of penetration of gold nanoparticles into PiBMA against ŵÈ˫ˠ ...53 ix CHAPTER 1 INTRODUCTION A surface can be defined as a transition region between one medium and another and is different from region 1 and region 2. The properties at the surface deviate from those in the bulk due to broken and strained bonds as well as reduced density of atoms/molecules. Particularly in polymers, these deviations at the surface substantially impact the mechanical properties [1 - 4]. One such mechanical property is the glass transition temperature (T g) [5, 6]. Investigations on polymer surfaces by various groups revealed that the surface T g (T gs ) is not equal to the bulk T g (T gb ) [7, 8]. While some groups claim that T gs of a polymer is lower than T gb [9 - 11], others claim that T gs is higher than T gb [12]. Yet, some other groups claim that there is no difference between Tgs and T gb [13, 14]. In 2001, Zaporojtchenko , Strunskus, Erichsen and Faupel introduced a new technique for probing the T gs of a polymer by the embedding of noble metal nanoparticles [23]. Later in 2003, Teichroeb and Forrest imaged 1 embedding of gold nanoparticles into polystyrene surface by atomic force microscopy. They suggested that there is a more mobile surface region of about 3-4 nm thick, indicative of a lower T g at the surface compared to the bulk [15]. However, in 2005 Hutcheson and McKenna presented an interpretation contrary to the results of Teichroeb and Forrest using a visco-elastic contact mechanics model [16, 17]. According to Hutcheson and McKenna, the embedding of gold nanoparticles was due to the indentation created by the large surface interaction between polystyrene and gold. Hence, they concluded that there is no possible existence of a so called “liquid layer” as proposed by Teichroeb and Forrest [16, 17]. After the controversy raised by these studies, it is understood that a better understanding of T g of a polymer at its surface has yet to be attained. In the present work however, instead of atomic force microscopy, a novel optical spectroscopic approach was pursued to monitor the localized surface plasmon resonance (LSPR) of the gold nanoparticles. The nanoparticles were coated on the surface of poly isobutyl methacrylate (PiBMA) by physical
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