Clemson University TigerPrints All Dissertations Dissertations 12-2013 NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES Thusitha Etampawala Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Part of the Physical Chemistry Commons Recommended Citation Etampawala, Thusitha, "NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES" (2013). All Dissertations. 1207. https://tigerprints.clemson.edu/all_dissertations/1207 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Chemistry by Thusitha N. B. Etampawala December 2013 Accepted by: Dr. Dvora Perahia, Committee Chair Dr. Christopher J. Cornelius Dr. Stephen Creager Dr. Steven J. Stuart i ABSTRACT This work focuses on interfacial structure and dynamics of structured polymers in thin films and in solutions using neutron techniques accompanied by atomic force microscopy. We probed polymers with a common theme that were highly segregated either because of presence of ionic groups or topological constraints. In these polymers the interfacial regions often define their function in different applications such as clean energy, printing adhesions and drug delivery systems. Thin film studies include systems of polystyrene/sulfonated polystyrene, a rigid sulfonated polyphenylene and polystyrene three-arm stars/linear polystyrene. The first two systems include ionic components and the last exhibits topological constraints. Polystyrene is often used as a model polymer because of the ease of exercising synthetic control over its molecular weight. Interdiffusion at the polymer-polymer interface was followed as well as diffusion of guest molecules. We found that the interfacial diffusion at the interfaces of ionic- nonionic polymers is strongly impacted by the presence of ions. The presence of ionic groups results in surface aggregation which in turn impacts the interfacial diffusion. The rigidity of the polymer also plays an important role as it results in significant interstitial spaces that dominate diffusion. The interfaces formed by these polymers are often inhomogeneous and contain both ionic and nonionic species that impact the onset of dynamics. In parallel, we studied the interfacial segregation of three-arm star polymers in a matrix of polystyrene. The contact point between the three-arms forms topological ii constraints that impact the segregation. The interfacial compositions were found to be balanced between entropic forces that drove polymer chain ends to the interfaces and the effects of topological constraints that hindered the motion of polymers. Interfacial segregation effects are seen not only in thin films but also strongly affect the assembly of polymers in solution. Here we studied a penta-block copolymer that consists of an ionic center block in hydrophobic solution. We found that very stable aggregates are formed where these shapes and stability are attributed to the ionic block. Finally the synthesis of structured alternating copolymers and their optical characteristics are introduced. iii DEDICATION This dissertation is dedicated to my wife, Madhubashini Medagoda, my mother, late father, my sister and my parents-in-law for their love and support given me throughout my life. Without them, I will be unable to make this achievement. iv ACKNOWLEDGMENTS First and foremost, I would like to express my sincere gratitude to my doctoral research advisors, Dr. Dvora Perahia for her guidance, encouragement and invaluable support given throughout my Ph.D. study. I would like to thank Dr. Christopher J. Cornelius (currently at Chemical & Biomolecular Engineering Department at University of Nebraska-Lincoln), Dr. Rhett Smith and Ms. Brynna Laughlin for their valuable guidance throughout the synthesis of some of the polymer materials used in this study. I am grateful to my dissertation committee, Dr. Christopher J. Cornelius, Dr. Steven J. Stuart and Dr. Stephen Creager for their suggestions and evaluation of my dissertation. Their advice and support have always been appreciated. I would like to thank some neutron beam line scientists including Dr. Jaroslaw Majewski (SPEAR at LANSCE, LANL), Dr. Rex Hjelm (LQD at LANSCE, LANL), Dr. Jim Browning, Dr. John F. Ankner and Ms. Candice Hilbert (LR at SNS, ORNL), Dr. William T. Heller and Dr. Christopher B. Stanley (EQ-SANS at SNS, ORNL), Dr. Lilin He (GP-SANS at HFIR, ORNL), for their priceless technical help and advices on the neutron scattering and reflectivity experiments. I would like to thank Dr. Don Vanderveer for his help on X-ray diffraction experiments. Special thank goes to my colleagues in our “polymer physics” research group at Clemson University particularly Dilru R. Ratnaweera, Naresh C. Osti, Umesh M. Shrestha, Sidath I. Wijesinghe, Dipak Aryal and Sabina Maskey for their support given me to success the neutron related experiments. Without them, I will be unable to make this work happen. v Further, I would like to thank Dr. Carl Willis from Kraton Polymers, US, LLC for the penta-block copolymer materials. Finally, I would like to acknowledge the financial support from College of Science and Engineering, Clemson University and United States Department of Energy. vi TABLE OF CONTENTS Page TITLE PAGE ................................................................................................................... i ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................ iv ACKNOWLEDGMENTS ............................................................................................... v LIST OF TABLES ........................................................................................................... x LIST OF FIGURES ........................................................................................................ xi CHAPTER I. INTRODUCTION ........................................................................................ 1 Ionomers ................................................................................................. 1 Motivation and objectives .................................................................. 1 Morphological models of ionomers ................................................... 5 Ionomers in solution ..................................................................... 7 Ionomers in thin film ..................................................................... 9 Polymers with topological constraints .................................................. 10 Motivation and objectives ................................................................ 10 Outline and contribution ...................................................................... 11 References ............................................................................................. 13 II. EXPERIMENTAL METHODS .................................................................. 18 Small angle scattering ........................................................................... 18 Small angle neutron scattering ....................................................... 23 Non-polarized specular neutron reflectivity ......................................... 25 References ............................................................................................. 30 III. INSIGHT INTO THE STABILITY OF POLYMER THIN FILM: EFFECTS OF THREE-ARM POLYSTYRENE STARS IN LINEAR POLYSTYRENE THIN FILMS AGAINST THERMAL ANNEALING ............................................................................................. 33 Abstract ................................................................................................. 33 Introduction ........................................................................................... 34 vii Table of Contents (Continued) Page Experimental .......................................................................................... 36 Samples ........................................................................................... 36 Thin films preparations ................................................................... 38 Silicon wafer treatment ................................................................... 38 Neutron reflectivity experiment ...................................................... 38 Analysis of the density profiles....................................................... 40 Results and discussion .......................................................................... 42 Summary ................................................................................................ 56 Supporting information .......................................................................... 57 Acknowledgement ................................................................................ 58 References .............................................................................................. 58 IV. NEUTRON REFLECTIVITY STUDY OF THE INTERFACIAL REGIONS BETWEEN IONOMERS AND VAN DER WAALS POLYMERS ..............................................................................................