DEPARTMENT OF PHYSICS UNIVERSITY OF JYVÄSKYLÄ RESEARCH REPORT No. 11/2018 DEVELOPMENT OF MICROFLUIDICS FOR SORTING OF CARBON NANOTUBES BY JÁN BOROVSKÝ Academic Dissertation for the Degree of Doctor of Philosophy To be presented, by permission of the Faculty of Mathematics and Science of the University of Jyväskylä, for public examination in Auditorium FYS1 of the University of Jyväskylä on December 13th, 2018 at 12 o’clock noon Jyväskylä, Finland December 2018 Preface The work reviewed in this thesis has been carried out during the years 2012 & 2014-2018 at the Department of Physics and Nanoscience Center in the University of Jyväskylä. First and foremost, I would like to thank my supervisor Doc. Andreas Jo- hansson for his guidance during my Erasmus internship and consequent Ph.D. studies. I am very grateful for his willingness to share both the professional com- petence and personal wisdom. Equal gratitude belongs to Prof. Mika Pettersson, without whom this project would never exist. His ability to see the big picture, his interesting insights, and genuine joy from the beauty of the microworld were a true motivation for me. It has been a great experience to work in the Nanoscience Center for all these years. I would like to express my gratitude to the whole staff for being supportive, sharing good ideas, or just having fun meaningful conversations. A special thanks goes to Prof. Janne Ihalainen for providing me access to the facilities of the Department of Biology. I humbly acknowledge the irreplaceable help of our technical staff, namely Dr. Kimmo Kinnunen, Mr. Tarmo Suppula, Dr. Pasi Myl- lyperkiö, Dr. Alli Liukkonen, and Dr. Petri Papponen. Their help and ability to guide me together with their readiness to keep things running were vital to this work. The patient support from the office staff of both Nanoscience Center and the Department of Physics is greatly acknowledged. In particular, I would like to mention Riitta-Liisa Kuittinen, who made me to feel like home. I would like to thank my officemates, flatmates, and friends. Heli, Saara, Elena, Heikki, Andrey, Vesa-Matti, Jyrki, Simon, Yaro, and Juraj. Without you, my life would certainly not be so lively and vivid. I owe unmeasurable gratitude to my parents, Milan and Anna, for bringing me up and shaping me to who I am. Similarly, I thank my sisters, Marta and Tereza, for being supportive and always willing to help. Lastly, I wish to thank my lovely wife Nunu for her limitless patience, sup- port, and love, especially during the moments when we were separated by dis- tance or by me working at nights. Financial support from the Academy of Finland and Department of Physics, University of Jyväskylä are gratefully acknowledged. Omina ad maiorem Dei gloriam. Jyväskylä, November 2018 Ján Borovský Abstract Borovský Ján Development of Microfluidics for Sorting of Carbon Nanotubes Jyväskylä: University of Jyväskylä, 2018, 199 p. (Research report/Department of Physics, University of Jyväskylä ISSN 0075-465X; 11/2018) ISBN 978-951-39-7634-7 (paper copy) ISBN 978-951-39-7635-4 (e-print) diss. Sorting of carbon nanotubes by their chirality is the current bottleneck in the way to their broad employment based on their exceptional electronic and optical properties. Despite the extensive effort, there is no known method, which would result in really pure chirality ensembles. Previously reported sorting protocols result in enrichment rather than in sorting, alter electronic structure, and suffer from low yield. This is mostly due to the statistical approach, where the nano- tubes with mixed chiralities are treated as a set. In this thesis, we propose a new sorting technique based on nanotube-by-nanotube compartmelization, character- ization, and sorting in a continuously running droplet-based microfluidic device. A new microfluidic platform for droplet-based experiments in femtoliter scale has been fully developed in this work. We report manufacture of full-glass spectroscopy-friendly microfluidic chips with the characteristic length of chan- nels below 3 μm. A novel procedure for immersed planar metallic electrodes suit- able for the harsh glass processing is introduced. Selective treatment of the chan- nels with a hydrophobic self-assembled monolayer is implemented for stable wa- ter-in-oil droplet microfluidics. Several unique properties of the system: the size, the unorthodox capacity of low droplet formation frequency, effective trap system, and tailored fluores- cence detection system, were developed with the aim of lowering the detection limit down to single nanotube level. The automated processing of fluorescence spectra triggers the dielectrophoretic sorting valve deflecting the nanotube car- rying droplets to either the reservoir or to the waste. Besides the primary goal, this microfluidic platform represents a powerful experimental tool to be em- ployed in various fields of research. A method of individualization of carbon nanotubes in an aqueous disper- sion based on sonication and centrifugation is systematically addressed in this thesis. The purity, level of individualization, quality of individualized nanotubes, and long-term stability are found to be critically dependent on the sonication pa- rameters, mainly the sonication power. For the purpose of water-in-oil droplet 6 microfluidics, a unique protocol for depletion of the surfactant at unaltered level of individualization is reported. The development described in this thesis brought the project to the very doorstep of automated carbon nanotubes sorting, one nanotube at the time. We believe that successful realization of the sorting would allow a major break- through in small-scale applications of single nanotube devices with precise chi- rality requirements for achieving the desired behavior. Keywords carbon nanotubes, sorting, individualization, dispersion, SDBS, soni- cation, centrifugation, long-term stability, near-infrared fluorescence, microflu- idics, glass microfabrication, wet etching, metallic electrodes, TADB, silinization, droplet-based, water-in-oil, decane, Span 80, low droplet formation frequency, passive trapping, dielectrophoresis, sorting, droplet stability, surface tension, in- terfacial tension 7 Author's address Ján Borovský Department of Physics University of Jyväskylä Finland Supervisors Senior Researcher Doc. Andreas Johansson Nanoscience Center Department of Physics University of Jyväskylä Finland Professor Mika Pettersson Nanoscience Center Department of Chemistry University of Jyväskylä Finland Reviewers Head of Work Group Dr. Thomas Henkel Department of Nanobiophotonics Leibniz Institute of Photonic Technology Germany Professor Yuri Svirko Institute of Photonics University of Eastern Finland Finland Opponent Professor Sami Franssila Department of Chemistry and Materials Science Aalto University Finland Contents Preface Abstract Contents 1 Introduction ........................................................................................................ 13 1.1 Carbon nanotubes ..................................................................................... 13 1.2 Microfluidics .............................................................................................. 14 1.3 The aim and content of the thesis ........................................................... 14 2 Carbon nanotubes – A review......................................................................... 19 2.1 Introduction ............................................................................................... 19 2.2 Atomic structure ....................................................................................... 20 2.3 Electronic structure ................................................................................... 21 2.4 Band structure ........................................................................................... 23 2.5 CNT characterization ............................................................................... 25 2.5.1 Direct characterization ................................................................. 25 2.5.2 Indirect characterization .............................................................. 26 2.6 CNT manufacture ..................................................................................... 30 2.7 Application issues ..................................................................................... 31 2.7.1 Sorting ............................................................................................. 32 2.7.2 Individualization ........................................................................... 36 2.8 Aqueous dispersions of SWCNTs .......................................................... 38 2.8.1 Choice of surfactant ...................................................................... 38 2.8.2 Concentration of nanotubes......................................................... 38 2.8.3 Amount of SDBS............................................................................ 39 2.8.4 Sonication ....................................................................................... 39 2.8.5 Centrifugation ................................................................................ 41 3 Carbon nanotubes – The dispersion .............................................................. 43 3.1 Reagents ..................................................................................................... 43 3.2 Instrumentation ......................................................................................... 46 3.2.1 Preparation