City University of New York (CUNY) CUNY Academic Works All Dissertations, Theses, and Capstone Projects Dissertations, Theses, and Capstone Projects 2-2014 Magnetic Janus Particles and Their Applications Bin Ren Graduate Center, City University of New York How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/gc_etds/99 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] Magnetic Janus Particles and Their Applications by Bin Ren A Dissertation Submitted to the Graduate Faculty in Chemistry in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy The City University of New York 2014 ii © 2014 Bin Ren All Rights Reserved iii This manuscript has been read and accepted for the Graduate Faculty in Chemistry in satisfaction of the dissertation requirements for the degree of Doctor of Philosophy. ________________________ ____________________________________ Date Dr. Ilona Kretzschmar Chair of Examining Committee ________________________ ____________________________________ Date Dr. Maria Tamargo Executive Officer ____________________________________ Dr. Charles Michael Drain ____________________________________ Dr. Orlin Velev ____________________________________ Dr. Jeffrey Morris Supervision Committee THE CITY UNIVERSITY OF NEW YORK iv Abstract Magnetic Janus Particles and Their Applications by Bin Ren Advisor: Ilona Kretzschmar Magnetic properties are important since they enable the manipulation of particle behavior remotely and therefore provide the means to direct a particle’s orientation and translation. Magnetic Janus particles combine magnetic properties with anisotropy and thus are potential building blocks for complex structures that can be assembled from a particle suspension and can be directed by external fields. In this thesis, a method for the fabrication of three types of magnetic Janus particles with distinct magnetic properties is introduced, the assembly behavior of magnetic Janus particles in external magnetic and electric fields is systematically studied, and two potential applications of magnetic Janus particles are successfully tested. Janus particles with different magnetic properties are fabricated by varying the deposition rate of iron in an Ar/O2 atmosphere using physical vapor deposition (PVD). The extent of oxidation for each type of iron oxide is precisely controlled by the time it is exposed to the Ar/O2 atmosphere during deposition. Two of the three magnetic Janus particles produced show distinct assembly behavior into staggered and double chain structures, whereas the third shows no assembly behavior under an external magnetic field. The effect of the iron oxide cap thickness (≤ 50 nm) on the Janus particle assembly behavior is studied resulting in a deposition rate diagram that shows the relationship between the assembly behavior and the deposition rate. The cap v materials for staggered chain, double chain, and no assembly behavior are assigned as Fe1-xO, Fe3O4, and Fe2O3, respectively, based on optical appearance and physical properties. The assignment is further confirmed by in-depth material characterization with scanning and transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The magnetic hardness of the iron oxides is tested using the magneto-optic Kerr effect. The assembly behavior of Fe3O4-capped Janus particles is studied in overlapping parallel and perpendicular AC electric and magnetic fields. The chains formed by Fe3O4-capped magnetic Janus particles show contraction behavior of ~30%, which suggests their application as an in situ viscometer. The chain contraction rate is found to depend on the viscosity of the liquid as well as the size of Janus particles and an in situ micro-viscometer is realized. Further, the magnetic dipole-dipole interactions of Fe1-xO and Fe3O4-capped Janus particles are studied by analyzing the particle-particle interaction force and energy during the process of Janus particle doublet formation. Using the magnetic particle interaction energy, the magnetization of each iron oxide cap is determined and found to be in excellent agreement with magnetization values obtained using standard SQUID measurements suggesting the application of magnetic Janus particles as a micro-magnetometer. In summary, three types of magnetic Janus particles with distinct magnetic properties have been fabricated and show versatile assembly behaviors that make them useful basic building blocks for complex structures and applications. For example, magnetic Janus particles can be used to measure the viscosity of a fluid or the magnetic property of a thin film cap material. It is likely that other interesting applications will emerge, when Janus particles of various sizes and/or patchy particles with magnetic properties are combined and explored. vi Acknowledgements First and foremost I want to thank my advisor Prof. Ilona Kretzschmar. She has taught me, both consciously and un-consciously, how well research can be done. I appreciate all her contribution of time, ideas, and funding to make my Ph.D. experience productive and stimulating. The joy and enthusiasm she has is contagious and motivating for me, even during tough times in my Ph.D. pursuit. I am also thankful for the excellent example she has provided as a successful researcher and professor. In addition, I would like to thank my thesis committee members, Prof. Charles Michael Drain, Prof. Jeffrey Morris, and Prof. Orlin Velev for their guidance and insightful discussions in the respective fields to further advance and improve this thesis work. The members of the Kretzschmar group have contributed immensely to my personal and professional time at CCNY. The group has been a source of friendships as well as good advice and collaboration. I am especially grateful for the help of the group members, who shared my graduate school experience with me: Dr. Jingqin Cui, Dr. Jung Hun (Kevin) Song, Dr. Amar Pawar, Dr. Sonia Mathews, Dr. Hsinyu Chen, Mr. Zhenping He, Mr. Roger Chang, Ms. Sepideh Razavi, and Mr. Weikang Chen. I would like to thank Ms. Shiqi Li from Prof. Myriam Sarachik’s group at the Physics Department of CCNY for the SQUID measurements, Mr. Zengyan Wei from Prof. Hiroshi Matsui’s group at the Chemistry Department of Hunter College for the HRTEM and EDS measurements, Dr. Qianfeng Xu from Prof. Alan Lyons’s group at the Chemistry Department of College of Staten Island for the XPS measurements, and Dr. Yu Gong from Prof. Yuhang Ren’s group at the Physics Department of Hunter College for the magneto-optic Kerr effect measurements. vii Lastly, I would like to thank my family for all their love and encouragement. I thank my parents Mr. Xinmin Ren and Mrs. Lingzhi Hong, who raised me with a love of science and supported me in all my pursuits. And most of all for my loving, supportive, encouraging, and inspiring wife Cheng whose faithful support during the final stages of this Ph.D. is so appreciated. Thank you!!! Bin Ren January 2014 Contents Chapter 1 Introduction………………………………………………………………….1 Chapter 2 Magnetically Anisotropic Particles……………………………..…………..5 2.1 Fabrication of Janus Particles with Magnetic Anisotropy……………………..…..5 2.1.1 Fabrication Methods Based on Phase Immiscibility…………………….…..6 2.1.2 Fabrication Methods Based on Templating……………………………...…12 2.1.3. Fabrication Methods Based on Directed Deposition………………………14 2.1.4 Fabrication Methods Based on Anisotropic Precursors………………...….15 2.2 Assembly of Janus Particles with Magnetic Anisotropy…………………..……..17 2.2.1 Self-assembly of Magnetic Janus Particles…………………….…………..17 2.2.2 Magnetic Field-directed Assembly…….……………………….…………..19 2.3 Application of Janus Particles with Magnetic Anisotropy……………………….22 2.3.1. Microrheology…………………………………………………….……….22 2.3.2. Micromotors……………………………………………………………….23 2.3.3. Displays, Switches, and Targeting Agents for Drug Delivery…………….23 2.3.4. Emulsion Stabilizers…………………………………………...…………..25 2.4. Conclusions………………………………………………………...……………25 Chapter 3 Fabrication of Iron Oxide Janus Particles and Their Assembly Behavior in Magnetic Field ...…………………………………………………………….……….26 3.1 Experimental Details…………………………………………………..…………27 3.2 Janus Particle Fabrication and Assembly……………………………….………..29 3.3 Results……………………………………………………………………………30 viii CONTENTS ix 3.4 Discussion………………………………………………………………………..38 3.5 Summary…………………………………………………………..……………..48 Chapter 4 Characterization of Iron Oxide Thin Films...…………………………….49 4.1 Surface Morphology Analysis using FE-SEM and AFM Methods…….………..50 4.2 Composition Analysis using EDS and XPS Methods………………..………....54 4.3 Crystal Structure Analysis using TEM and HRTEM……………………...…….58 4.4 Magnetic Analysis using Magneto-optic Kerr Effect Measurements…….……..61 4.5 Summary………………………………………………………..………………..63 Chapter 5 Field-directed Assembly of Iron Oxide Janus Particles………...………..65 5.1 Experimental Details……………………………………………………………..66 5.2 Results………………………………………………………………..…………..69 5.2.1 Application of Parallel AC Electric and Static Magnetic Field.……………70 5.2.2 Application of Perpendicular AC Electric and Static Magnetic Field...……72 5.2.3 Application of Parallel Static Magnetic and AC Electric Field…………….75 5.2.4 Application of Perpendicular Static Magnetic and AC Electric Field..…….76 5.3 Discussion……………………………………………………………..…………78 5.4 Summary……………..…………………………………………….…………….83