Universite´ Pierre et Marie Curie Specialite´ : Chimie Physique ED 388 { Chimie Physique et Chimie Analytique de Paris Centre These` de Doctorat Colloidal Interactions in Ionic Liquids Interactions Collo¨ıdalesDans Les Liquides Ioniques Auteur: Directrice de th`ese: Marianna Mamusa Dr. V´eronique Peyre Travail de th`esesoumis pour obtenir le grade de Docteur de l'Universit´ePierre et Marie Curie et d´eroul´eau Laboratoire PHENIX - PHysicochimie des Electrolytes et Nanosyst`emesInterfaciauX Th`esesoutenue le 25 F´evrier2014 devant le jury compos´ede: Werner KUNZ, Professeur Rapporteur Andr´eVIOUX, Professeur Rapporteur Julian OBERDISSE, Directeur de Recherche Examinateur Corinne CHANEAC, Professeur Examinatrice V´eroniquePEYRE, Ma^ıtrede Conf´erences Directrice de th`ese Contents List of Figures vii List of Tables xi Abbreviations xiii Introduction1 1 Background5 1.1 Interactions between atoms, molecules, particles...............6 1.1.1 General Considerations on Electrostatic Forces...........6 1.1.2 Dipolar Magnetic Interactions..................... 11 1.1.3 Van der Waals Forces between Atoms and Molecules........ 12 1.1.4 Steric Contributions and Total Interaction Potential........ 15 1.1.5 DLVO Theory............................. 17 1.2 The Colloids: Maghemite Nanoparticles................... 22 1.3 Ionic Liquids.................................. 28 1.3.1 Ethylammonium Nitrate........................ 30 1.4 Ionic Liquids in Colloidal Systems: State of the Art............ 34 1.4.1 Ionic Liquids as a Medium for the Synthesis of Nanoparticles... 34 1.4.2 Colloidal Dispersions in Ionic Liquids................ 35 1.4.3 ILs at a Surface............................. 45 1.4.4 Interparticle Potential in ILs..................... 52 1.5 Conclusion................................... 55 2 Materials and Methods 57 2.1 Materials.................................... 58 2.2 Syntheses and Functionalizations....................... 58 2.2.1 Synthesis of Maghemite Nanoparticles................ 58 2.2.2 Size Sorting of Maghemite Nanoparticles............... 60 2.2.3 Preparation of Acidic and Alkaline Ferrofluids with Different Counter- ions................................... 62 2.2.4 Surface Functionalization with Citrate Ligands........... 63 2.2.5 Synthesis of the Ionic Liquid Ethylammonium Nitrate....... 64 2.2.6 Synthesis of the Choline-Amino Acid ([Cho][AA]) Ionic Liquids.. 64 2.2.7 Transfer of Nanoparticles from Water to IL............. 65 2.2.8 Lyophilization............................. 67 iii iv Contents 2.3 Characterization Techniques.......................... 67 2.3.1 Karl Fischer Titration......................... 67 2.3.2 pH Measurements in Ethylammonium Nitrate............ 68 2.3.3 Flame Atomic Absorption Spectroscopy............... 69 2.3.4 Small Angle (Neutron and X{Ray) Scattering............ 70 2.3.5 Dynamic Light Scattering....................... 71 2.3.6 Magnetization Measurements..................... 73 2.3.7 Magneto-Optical Birefringence Experiments............. 74 3 Preliminary Screenings on Polydisperse Nanoparticle/Ethylammonium Nitrate Dispersions 75 3.1 pH Measurements in Ethylammonium Nitrate................ 76 3.1.1 Response of the Glass Electrode in EAN............... 77 3.1.2 Dissociation Constants of Citric Acid in EAN............ 78 3.2 Dispersions of Bare Maghemite Nanoparticles in EAN: Effect of pH, Counterion and Water Content........................ 80 3.2.1 Neutral Medium { Point of Zero Charge............... 82 3.2.2 Acidic Medium............................. 82 3.2.3 Alkaline Medium............................ 84 3.3 Dispersions of Citrate-Covered Maghemite Nanoparticles in EAN..... 84 3.4 Microscopic Study of Citrate-Covered Maghemite Nanoparticles in EAN. 86 3.4.1 Dynamic Light Scattering Experiments............... 88 3.4.2 Small Angle Neutron Scattering (SANS) Experiments....... 90 3.5 Conclusion................................... 93 4 Dispersions of Size-Sorted Maghemite Nanoparticles in the IL Ethyl- ammonium Nitrate 95 4.1 Introduction................................... 96 4.2 Preparation and Chemical Analysis of the Samples............. 97 4.3 Evolution During the Preparation of the Samples: the Special Case of Lithium..................................... 102 4.4 Effect of NP Size and Concentration..................... 104 4.5 Small Particles (7 nm): Effect of the Counterion.............. 110 4.5.1 Dilute Regime............................. 110 4.5.2 Concentrated Regime......................... 111 4.6 Large Particles (11 nm): Effect of the Counterion.............. 118 4.6.1 Dilute Regime............................. 118 4.6.2 Concentrated Regime......................... 119 4.7 Discussion on the Effect of the Counterions on Both Sizes......... 128 4.8 Effect of Water Content............................ 131 4.9 Conclusion................................... 137 5 Tests with Cholinium-based Ionic Liquids 139 5.1 Introduction................................... 139 5.2 Dispersion of Maghemite Nanoparticles in Cholinium-Aminoacid ILs... 142 5.3 Dispersions of Maghemite in Water/[Cho][Gly] Media........... 144 5.4 Conclusion................................... 145 Contents v Conclusions and Perspectives 147 A Dispersions of Different Nanoparticles in Ionic Liquids 151 B Small Angle Scattering Techniques 157 B.1 Theoretical Principles............................. 157 B.2 Experimental Intensity and Absolute Intensity............... 159 B.3 Form Factor and Structure Factor...................... 160 B.4 Calculation of Scattering Length Densities and Contrast.......... 161 B.5 The Scattering Invariant. Calculation of Φ.................. 164 B.6 Guinier Plot................................... 165 B.7 Experimental Form Factors, P(Q)...................... 165 Bibliography 169 List of Figures 1.1 Electric Double Layer at a Charged Surface in Water............ 10 1.2 Van der Waals Interaction between Surfaces................. 14 1.3 Full Pair Potentials for Molecules and Particles............... 17 1.4 DLVO Energy vs. Distance Profiles...................... 18 1.5 TEM Image of Maghemite Nanoparticles................... 22 1.6 Stability of Maghemite Nanoparticles as a Function of pH......... 24 1.7 Dependence of the Structural Charge of Maghemite NP on the pH.... 25 1.8 Stability of Citrate-Covered Maghemite Nanoparticles as a Function of pH 25 1.9 Phase Diagrams for Citrate-Covered Maghemite Nanoparticles in Water. 26 1.10 Common IL Cations.............................. 28 1.11 Molecular Formula of Ethylammonium Nitrate............... 31 1.12 H-bond Networks of EAN and Water..................... 32 1.13 ZnO nanostructures synthesized in ILs.................... 35 1.14 IL Layers at the Bare Maghemite Surface.................. 37 1.15 Different Colloidal Stability of Bare and PMMA-Grafted Silica Particles. 41 1.16 Silica-based Ionogels.............................. 43 1.17 AFM Force Profile............................... 46 1.18 DLVO Interparticle Potential for Silica Particles in ILs........... 53 1.19 DLVO Interparticle Potential for Magnetite Particles in ILs........ 54 2.1 Size Distribution of Unsorted Maghemite Nanoparticles.......... 59 2.2 Destabilization of Maghemite Nanoparticles by Ionic Strength....... 60 2.3 Size Sorting of Maghemite Nanoparticles................... 61 2.4 Size Distribution of Size-Sorted Maghemite Nanoparticles......... 62 2.5 Reaction between Choline Hydroxide and an Amino Acid......... 65 2.6 Synthesis of Cho-AA Ionic Liquids...................... 66 2.7 Process 1 for the Transfer of NP from Water to IL............. 66 2.8 Process 2 for the Transfer of NP from Water to IL............. 66 2.9 Karl Fischer................................... 68 2.10 Sample Preparation for SAXS......................... 71 3.1 Response of a Glass Electrode in Basic EAN Solutions........... 78 3.2 Response of a Glass Electrode in EAN.................... 79 3.3 Different States of Dispersion......................... 82 3.4 Citrate Anion.................................. 85 3.5 DLS Experiments on Some Citrated NP................... 89 3.6 SANS Experiments on Polydisperse Maghemite Dispersions in EAN and Water...................................... 90 vii viii List of Figures 3.7 Fits of SANS Intensities for Three Representative Cases in Water and EAN 91 4.1 Separation of Particles and Solvent by Centrifugation........... 97 4.2 UV-Vis Absorption Spectra for FeNSA-5 Complex in EAN......... 99 4.3 Calibration Curve for the FeNSA-5 Complex in EAN............ 99 4.4 UV-Vis Absorption Spectra for FeNSA-5 Complex in EAN......... 100 4.5 Effect of Ageing on Li+/EAN Dispersione.................. 103 4.6 Effect of Ageing on Li+/EAN Dispersione.................. 103 4.7 Optical Microscopy under Magnetic Field: Reversible Phase Separation. 105 4.8 Coexistence of Dilute and Concentrated NP Phases (Large Particles)... 106 4.9 Optical Microscopy of the Coexistence of Dilute and Concentrated NP Phases...................................... 107 4.10 Schematic Phase Diagram for a Colloidal System.............. 107 4.11 S(Q) Plots for Dilute Dispersions of Small NP in EAN with Different Counterions................................... 111 4.12 I(Q) Plots for Small Particles with Different Counterions.......... 112 4.13 Magneto-Optic Birefringence Relaxation Curves for Small Particles with Different Counterions.............................. 112 4.14 Effect of Small NP Concentration of the S(Q) in the Case of Li+ Counterions114 4.15 Structure Factors for Dilute Suspensions of Large Particles........ 118 4.16 Magneto-optic Birefringence Experiments