The Use of Two-Dimensional Suspensions for the Fundamental Study of the Dynamics of Colloidal Suspensions and their Technological Applications (Gebruik van twee-dimensionale suspensies voor fundamentele studies van de dynamica van colloidale systemen en hun technologische toepassingen)

De invloed van uitwendige velden op colloidale deeltjes aan vloeistof-vloeistof interfasen worden bestudeerd in dit werk. De interactie potentiaal tussen twee deeltjes die gepind zijn aan een interfase is experimenteel bepaald. Wanneer aggregatie word geinduceerd, bekomt men een model systeem dat gebruikt kan worden om typische eigenschappen van colloidale dispersies te bestuderen, zoals yielden, thixotropie en het onstaan van ansiotropie. De structurele organsiatie van de colloidale deeltjes onder invloed van electrische velden worden bestudeerd.Contents Acknowledgements i Contents iii Samenvatting xi Summary xiii List of symbols xv 1 Introduction 1 1.1 Motivation for studying particles at interfaces . . . . . . . . . . . . 1 1.1.1 Colloidal systems . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.2 Colloids as model systems . . . . . . . . . . . . . . . . . . . 1 1.1.3 Stabilization of mixtures of immiscible fluids . . . . . . . . 3 1.1.4 High quality products . . . . . . . . . . . . . . . . . . . . . 5 1.2 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Materials and methods 7 2.1 Model monolayer experiments . . . . . . . . . . . . . . . . . . . . . 7 2.2 Two-dimensional flow fields . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Shear flow fields . . . . . . . . . . . . . . . . . . . . . . . . 12 2.2.2 Extensional and rotational flow fields . . . . . . . . . . . . . 12 2.2.3 Converging and capillary flow fields . . . . . . . . . . . . . 14 2.3 2D Rheology experiments . . . . . . . . . . . . . . . . . . . . . . . 16 2.4 2D Electric Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.4.1 Normal electric fields . . . . . . . . . . . . . . . . . . . . . . 17 2.4.2 In-plane electric fields . . . . . . . . . . . . . . . . . . . . . 18 2.5 Image analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.5.1 Local structural descriptors . . . . . . . . . . . . . . . . . . 20 2.5.2 Global structural descriptors . . . . . . . . . . . . . . . . . 23 2.5.3 Overview of parameters and IDL routines . . . . . . . . . . 25 iii 3 Colloids at interfaces: interactions 27 3.1 Colloids in bulk: overview . . . . . . . . . . . . . . . . . . . . . . . 27 3.2 Colloids at interfaces: state of the art . . . . . . . . . . . . . . . . 30 3.2.1 Static properties . . . . . . . . . . . . . . . . . . . . . . . . 30 3.2.2 Forces between particles at interfaces . . . . . . . . . . . . . 31 3.2.3 What changes for nano-particles at interfaces? . . . . . . . 39 3.3 Pair interactions at liquid interfaces . . . . . . . . . . . . . . . . . 40 3.3.1 Contact-angle measurements . . . . . . . . . . . . . . . . . 40 3.3.2 Repulsive interactions . . . . . . . . . . . . . . . . . . . . . 41 3.3.3 Attractive interactions . . . . . . . . . . . . . . . . . . . . . 57 3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 3.5 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4 Colloids at interfaces: effect of flow fields 67 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 4.1.1 Structure of suspensions . . . . . . . . . . . . . . . . . . . . 67 4.1.2 Suspension rheology and modeling . . . . . . . . . . . . . . 76 4.1.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.2 Yielding in shear flow . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.2.2 Characterization of the initial microstructure . . . . . . . . 84 4.2.3 Characteristic length scales under quiescent conditions . . . 86 4.2.4 Structural rearrangements under shear flow start-up . . . . 90 4.2.5 Comparison with theoretical models . . . . . . . . . . . . . 101 4.3 Yielding in complex flows . . . . . . . . . . . . . . . . . . . . . . . 105 4.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.3.2 Behavior in shear flow of a pre-sheared network . . . . . . . 106 4.3.3 Behavior in rotational flow . . . . . . . . . . . . . . . . . . 106 4.3.4 Behavior in extensional flow . . . . . . . . . . . . . . . . . . 109 4.3.5 Converging flow . . . . . . . . . . . . . . . . . . . . . . . . 114 4.3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4.4 Flow-induced structures and anisotropy . . . . . . . . . . . . . . . 122 4.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 122 4.4.2 Results and discussion . . . . . . . . . . . . . . . . . . . . . 123 4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 5 Colloids at interfaces: effect of electric fields 145 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 5.2 Field lines normal to the interface . . . . . . . . . . . . . . . . . . 148 5.2.1 Determination of the electric fields . . . . . . . . . . . . . . 148 5.2.2 Forces induced by an electric field . . . . . . . . . . . . . . 150 5.2.3 Uncharged particles . . . . . . . . . . . . . . . . . . . . . . 153 5.2.4 Charged particles . . . . . . . . . . . . . . . . . . . . . . . . 159 iv 5.2.5 Mixtures of particles . . . . . . . . . . . . . . . . . . . . . . 162 5.3 Field lines parallel to the interface . . . . . . . . . . . . . . . . . . 170 5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 6 Conclusions and outlook 179 Notes and references 183 List of publications 203 Curriculum Vitae 205nrpages: 227status: publishe

Chronoamperometric study of membrane electrode assembly operation in continuous flow photoelectrochemical water splitting

Water splitting was performed in a photoelectrochemical cell (PEC) with water oxidation and hydrogen formation reactions in two separate compartments. A photoanode consisting of carbon paper loaded with TiO2 and a cathode made of Pt dispersed on carbon black spread also on carbon paper were fixed on both sides of a Nafion membrane and electrically coupled via an external circuit. Anode and cathode compartments with serpentine flow field were operated either in liquid or vapor phase. Electrical current was monitored with chronoamperometry and D2 formation from deuterated water using mass spectrometry. Mapping the photocurrent under a variety of reaction conditions enabled identification of the limiting factors related to proton and photocarrier transport and reaction product evacuation. This comprehensive research approach to the operation of a PEC will assist future optimization of cell design and development of membrane electrode assemblies.http://pubs.rsc.org/en/content/articlelanding/2013/cp/c3cp50890kstatus: publishe

Finite ion-size effects dominate the interaction between charged colloidal particles at an oil-water interface

The electrostatic interaction of charged spherical colloids trapped at an interface between a nonpolar medium and water is analyzed. Complementary experiments provide consistent values for the dipoledipole interaction potential over a wide range of interparticle distances. After accounting for the contribution from the compact inner double layer arising from the finite size of the counterions, we demonstrate quantitative agreement between experiments and nonlinear Poisson-Boltzmann theory. We find that the inner layer contribution dominates the electrostatic interaction in the far field for particles pinned at the interface. This result is fundamentally different from screened electrostatic interactions in the bulk and could contribute to the further understanding of the structure of the compact counterion layer in highly charged systems.status: publishe

Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition

Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 ± 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces.status: publishe

Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition

Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino) titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 +/- 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces

Anisotropic atomic layer deposition profiles of TiO₂ in hierarchical silica material with multiple porosity

Anisotropic deposition profiles of TiO2 in Zeotile-4 ordered mesoporous silica material are obtained using Atomic Layer Deposition (ALD) involving alternating pulses of tetrakis(dimethylamino) titanium (TDMAT) and water. TiO2 concentration profiles visualized by transmission electron microscopy (TEM) on particle cross sections reveal the systematic deeper penetration of the deposition front along the main channels and the more limited penetration in the perpendicular direction through the narrower slit-like mesopores. In ordered mesoporous material with one-dimensional pore system ALD leads to pore plugging. Diffusion limited ALD is shown to be useful for TiO2 deposition in anisotropic mesoporous support materials

Letter to the editor regarding the article by Wittmaack

status: publishe