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Preparation of Janus Nanoparticles and Its PREPARATION OF JANUS NANOPARTICLES AND ITS APPLICATION IN OIL INDUSTRY A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Wenhao Li August 2019 PREPARATION OF JANUS NANOPARTICLES AND ITS APPLICATION IN OIL INDUSTRY Wenhao Li Thesis Approved: Accepted: _______________________________ _______________________________ Advisor Department Chair Dr. Younjin Min Dr. Mark D. Soucek _______________________________ _______________________________ Committee Member Interim Dean of the College Dr. Thein Kyu Dr. Ali Dhinojwala _______________________________ _______________________________ Committee Member Dean of the Graduate School Dr. Sadhan C. Jana Dr. Chand Midha _______________________________ Date ii ABSTRACT Janus nanoparticles, named after the two-faced Roman god, possess anisotropic interfacial, chemical, and physical properties at their two different “faces”. Recently, Janus nanoparticles have received increasing attention in the literature owing to their unique individual and collective properties. Such colloids have been used or considered to be utilized in the areas of emulsion stabilizers, viscosity modifiers, microreactors, pho- tonic materials, and enhanced oil recovery. The main objective of this work is to develop new synthesis approaches for large-scale production of monodisperse Janus nanoparticles and to investigate the influence of hydrophilic-lipophilic balance, relative areas of anisotropic faces, and particle size on the phase behavior of oil-water-nanoparticle ternary mixtures as well as the colloidal stability of Janus particles themselves and their Pickering emulsions (oil-in-water emulsions stabilized by Janus nano-particles). This work has mainly focused on precisely fabricating surface modified Janus nanoparticles based on a controlled sinking process. For this purpose, first, highly monodisperse spherical silica particles with diameters of 50 and 400 nm were synthesized through the modified Stöber method. The morphology and size of silica nanoparticles were characterized using Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS) techniques. The zeta potential measurements revealed a surface charge of -40 to -45 mV for silica nanoparticles, indicating that the sufficient electrostatic surface charges were attained, giving rise to a fairly stable dispersion in aqueous solution. iii Highly ordered two-dimensional colloidal monolayers were attempted to be fabricated onto poly (methyl methacrylate) (PMMA) coated substrates using the Langmuir-Blodgett (LB) deposition technique. The pressure-area isotherms of silica nanoparticles at the air- water interface demonstrate a roughly linear-dependence between interfacial area (A) and surface pressure () up to ≈ 25 mN/m. Above this set point, surface pressure stayed constant with decreasing A, indicative of collapsing colloidal monolayers from the interface to the subphase. The hysteresis between expansion and compression isotherm cycles was found as a clear sign of the irreversible directed assembly processes. A well- ordered, packed monolayer of silica nanoparticles could be obtained at a surface pressure of 10 mN/m as a result of attractive van der Waals interactions that could be promoted upon reaching below a critical interparticle separation. The exposed (unembedded) areas of the colloidal monolayers were carefully controlled by heating the PMMA matrix at pre-determined temperatures and subsequently, modified by interfacially active ligands (e.g. chlorosilanes) through a chemical vapor deposition (CVD) method in order to achieve Janus characteristics. Contact angle measurements were also performed to qualify and quantify the wetting dynamics of Janus nanoparticles fabricated of which characteristics are found to be susceptible to ligand concentration as well as exposure time. Overall, it is anticipated that novel amphiphilic Janus nanoparticles fabricated through this study could significantly advance the current state-of-the-art in emulsion stability issues arising in many industrial processes including enhanced oil recovery. iv ACKNOWLEDGMENTS I would like to express my deep gratitude to Professor Younjin Min, my research advisor, for her patient guidance, enthusiastic encouragement and useful critiques of this research work. I would also like to thank Dr. Yuanzhong Zhang, for his advice and assistance in keeping my progress on schedule. My grateful thanks are also extended to Dr. Alessandro Perego, Dr. Stephen Merriman, Mr. Yuchen Zuo, Mr. Shifeng Huang, Mr. Wenhe Chen and Mr. Rundong Huang, my lab mates, for helping my research when I met problems. I would also like to extend my thanks to the technicians of the laboratory for their help in offering me the resources in running the program. Finally, I want to thank my parents for their support and encouragement throughout my study. v TABLE OF CONTENTS Page LIST OF FIGURES ...................................................................................................................... viii LIST OF TABLES ......................................................................................................................... ix LIST OF EQUATIONS ................................................................................................................... x LIST OF ILLUSTRATIONS .......................................................................................................... xi CHAPTER I. INTRODUCTION ........................................................................................................................ 1 II. FOUNDATION THEORY OF STUDY ..................................................................................... 4 2.1 Enhanced Oil Recovery ................................................................................................... 4 2.2 Janus Particles .................................................................................................................. 5 2.3 Pickering Emulsion .......................................................................................................... 6 2.4 Janus Particles Stabilized Pickering Emulsion ................................................................ 7 2.5 Synthesis of Monodispersed Silica Nanoparticles ........................................................... 8 2.6 Langmuir-Blodgett Technique....................................................................................... 11 2.7 Dip Coating .................................................................................................................... 14 2.8 Chemical Vapor Deposition Technique ......................................................................... 15 2.9 Dynamic Light Scattering .............................................................................................. 16 2.10 Zeta Potential ............................................................................................................... 17 2.11 Scanning Electronic Microscope ................................................................................. 18 2.12 Goniometer Measured Sessile Drop Contact Angle .................................................... 19 vi III. EXPERIMENTAL SECTION ................................................................................................. 21 3.1 Chemicals ...................................................................................................................... 21 3.2 Synthesis of 400nm Silica Nanoparticles ...................................................................... 21 3.3 Synthesis of 50nm Silica Nanoparticles ........................................................................ 22 3.4 Purification of 400nm Particles ..................................................................................... 23 3.5 Preparation of PMMA Film ........................................................................................... 24 3.6 Preparation of Langmuir-Blodgett Film ........................................................................ 24 3.7 PMMA Sinking .............................................................................................................. 26 3.8 Grafting of Ligands using Chemical Vapor Deposition ................................................ 27 3.9 Characterization of Size and Morphology of Nanoparticles.......................................... 27 IV. RESULT AND DISCUSSION ................................................................................................ 29 4.1 Synthesis of Monodispersed Silica Nanoparticles ......................................................... 29 4.2 Purification of Monodispersed Silica Nanoparticles ..................................................... 32 4.3 Preparation of PMMA Film on Glass Substrates by Dip Coating ................................. 36 4.4 Preparation of Colloid Monolayers with Langmuir-Blodgett Method .......................... 38 4.5 PMMA Sinking .............................................................................................................. 44 4.6 Grafting of Ligands using Chemical Vapor Deposition ................................................ 46 V. SUMMARY .............................................................................................................................. 50 BIBLIOGRAPHY .......................................................................................................................... 52 vii LIST OF FIGURES Figure Page 1.1
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