Adhesion and Wear of Nanoscale Polymer Contacts
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University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2017 Adhesion And Wear Of Nanoscale Polymer Contacts Yijie Jiang University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Mechanical Engineering Commons, and the Nanoscience and Nanotechnology Commons Recommended Citation Jiang, Yijie, "Adhesion And Wear Of Nanoscale Polymer Contacts" (2017). Publicly Accessible Penn Dissertations. 2362. https://repository.upenn.edu/edissertations/2362 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/2362 For more information, please contact [email protected]. Adhesion And Wear Of Nanoscale Polymer Contacts Abstract Atomic force microscopy (AFM) is a powerful tool for high resolution surface measurements, nanolithography, and tip-based nanomanufacturing. An understanding of the nanoscale tribological behavior of the tip-sample contact, including adhesion and wear, is critical in these applications. In this dissertation, the adhesion and wear of polymethyl methacrylate (PMMA) in contact with an ultrananocrystalline diamond (UNCD) AFM tip is investigated using a combination of AFM-based nanomechanics experiments and finite element analysis (FEA). A novel AFM-based method, which combines pull-off force measurements and characterization of the 3D geometry of AFM tip, was developed to quantify the properties of the adhesive traction-separation relationship of UNCD-PMMA contacts. Adhesion range and strength, as well as work of adhesion, of the contacts were determined. Characterizing and understanding nanoscale wear of polymers has proven difficult in the past dueo t experimental complications associated with debris produced in the tests and the failure of traditional empirical wear relations, such as Archard’s law. Here, nanoscale AFM-based line and raster wear experiments were performed on patterned PMMA structures, which had gaps that allow debris to be captured. Results from the line wear tests indicate that the relationship between height loss rate and stress is well described by a transition state theory wear model. The wear parameters obtained from line wear tests were applied to predict the volume loss in raster wear tests. Despite the significant differences in the loading and sliding geometry between line and raster wear experiments, the raster wear behavior was accurately predicted from the parameters obtained from line wear tests. In addition, experiments at varying temperatures were performed to study the temperature dependence of polymer wear. The results suggest that transition state theory overestimates the effect of temperature on wear for PMMA. Modified models considering viscoelastic elaxationr of PMMA and atom-by-atom attrition were applied to describe the measured wear behavior. Finally, an iterative FEA method was developed for simulations of wear. These simulations were used to examine the evolution of geometry and stress during the wear process as a function of contact conditions, such as friction and surface roughness. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Mechanical Engineering & Applied Mechanics First Advisor Kevin T. Turner Keywords Adhesion measurements, AFM-based nanomechanics, Finite element analysis, Nanoscale wear, Polymer contacts, Transition state theory Subject Categories Mechanical Engineering | Nanoscience and Nanotechnology This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/2362 ADHESION AND WEAR OF NANOSCALE POLYMER CONTACTS Yijie Jiang A DISSERTATION in Mechanical Engineering and Applied Mechanics Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2017 Supervisor of Dissertation ______________________________________________________________ Kevin T. Turner, Professor, Mechanical Engineering and Applied Mechanics Graduate Group Chairperson ______________________________________________________________ Kevin T. Turner, Professor, Mechanical Engineering and Applied Mechanics Dissertation Committee Robert W. Carpick John Henry Towne Professor, Mechanical Engineering and Applied Mechanics David J. Srolovitz Joseph Bordogna Professor, Materials Science and Engineering ACKNOWLEDGMENTS I would like to sincerely express my gratitude to my advisor Prof. Kevin Turner for his guidance and support with my research. Prof. Turner is always encouraging, patient and inspiring throughout the progression to complete this work. I gratefully acknowledge Prof. Robert Carpick and Prof. Judith Harrison for suggestions and support in the nanoscale wear project. I thank Prof. Tevis Jacobs, Prof. David Schall, Dr. Vahid Vahdat, Dr. Rodrigo Bernal and Zachary Milne for collaboration and discussion. I would also like to acknowledge Dr. Matthew Brukman for his training and great assistance in atomic force microscopy. I enjoy working with Prof. Daeyeon Lee and Jyo Lyn Hor in nanocomposite project, and Prof. John Hart and Dr. Sanha Kim in carbon nanotube project. I am thankful for their advice and collaboration. These experiences have broadened my knowledge and will benefit me in the future. I wish to thank my friends and colleagues Helen Minsky, Nathan Ip, Dr. Michael Wald, Lisa Mariani, and the other past and present members of the Turner Research Group for their helpful discussions, useful suggestions and friendship over the past five years. I would like to gratefully thank my family for their support during this endeavor and throughout my life. Xin, my lovely wife, is always a source of encouragement, company and love. My parents, Shidong and Fuqin, receive my deepest gratitude and love for their dedication and education. ii ABSTRACT ADHESION AND WEAR OF NANOSCALE POLYMER CONTACTS Yijie Jiang Kevin T. Turner Atomic force microscopy (AFM) is a powerful tool for high resolution surface measurements, nanolithography, and tip-based nanomanufacturing. An understanding of the nanoscale tribological behavior of the tip-sample contact, including adhesion and wear, is critical in these applications. In this dissertation, the adhesion and wear of polymethyl methacrylate (PMMA) in contact with an ultrananocrystalline diamond (UNCD) AFM tip is investigated using a combination of AFM-based nanomechanics experiments and finite element analysis (FEA). A novel AFM-based method, which combines pull-off force measurements and characterization of the 3D geometry of AFM tip, was developed to quantify the properties of the adhesive traction-separation relationship of UNCD-PMMA contacts. Adhesion range and strength, as well as work of adhesion, of the contacts were determined. Characterizing and understanding nanoscale wear of polymers has proven difficult in the past due to experimental complications associated with debris produced in the tests and the failure of traditional empirical wear relations, such as Archard’s law. Here, nanoscale AFM-based line and raster wear experiments were performed on patterned PMMA structures, which had gaps that allow debris to be captured. Results from the line wear tests iii indicate that the relationship between height loss rate and stress is well described by a transition state theory wear model. The wear parameters obtained from line wear tests were applied to predict the volume loss in raster wear tests. Despite the significant differences in the loading and sliding geometry between line and raster wear experiments, the raster wear behavior was accurately predicted from the parameters obtained from line wear tests. In addition, experiments at varying temperatures were performed to study the temperature dependence of polymer wear. The results suggest that transition state theory overestimates the effect of temperature on wear for PMMA. Modified models considering viscoelastic relaxation of PMMA and atom-by-atom attrition were applied to describe the measured wear behavior. Finally, an iterative FEA method was developed for simulations of wear. These simulations were used to examine the evolution of geometry and stress during the wear process as a function of contact conditions, such as friction and surface roughness. iv TABLE OF CONTENTS ACKNOWLEDGMENTS ............................................................................................................. ii ABSTRACT .................................................................................................................................. iii LIST OF TABLES ...................................................................................................................... viii LIST OF ILLUSTRATIONS ....................................................................................................... ix CHAPTER 1: Introduction ...................................................................................................... 1 1.1 Introduction and motivation ...................................................................... 1 1.2 Objectives..................................................................................................... 6 1.3 Scope............................................................................................................. 6 CHAPTER 2: Literature review .......................................................................................... 10 2.1 Adhesion mechanics .................................................................................. 10 2.1.1 Adhesion models