Understanding the lateral movement of particles adsorbed at a solid-liquid interface (original) (raw)
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Journal of Colloid and Interface Science, 2014
Adsorption of colloidal nanoparticles (NPs) at solid-liquid interface is a scientifically interesting and technologically important phenomenon due to its fundamental importance in many industrial, environmental, and biological processes, such as wastewater treatment, printing, coating of surfaces, chromatography, papermaking, or biocompatibility. The process is well understood theoretically by the random sequential adsorption (RSA) model, based on the assumption of irreversible adsorption. Irreversible adsorption is defined as a process in which, once adsorbed, a particle can neither desorb, nor to move laterally on the surface. However, published experimental data that verifies the irreversibility of particle adsorption are very limited. In this study, we demonstrate the irreversibility of electrostatically driven nanoparticle adsorption utilizing a carefully selected set of experiments. A simple method was employed by uniquely introducing Ag@SiO 2 core/shell NPs to perform exchange adsorptions experiments. Stöber SiO 2 NPs with a diameter of 50-80 nm were initially electrostatically adsorbed onto amino-functionalized silicon wafer substrates followed by the subsequent adsorption of Ag@SiO 2 NPs. The Ag@SiO 2 NPs have the same surface chemistry as the neat SiO 2 NPs. For the second step the adsorption time was varied from 1 min to 1 week so as to get a thorough understanding of the process irreversibility. Surface coverage quantification has shown that the surface coverage of the initially adsorbed SiO 2 NPs stays the same independent of the duration of the second step adsorption using the Ag@SiO 2 core/shell NPs. This observation directly confirms the irreversibility of electrostatic adsorption of NPs. Published by Elsevier Inc.
2009
Single particle tracking with a wide field microscope is used to study the solid liquid interface between the viscous liquid tetrakis(2-ethylhexoxy)-silane and a silicon dioxide surface. Silicon dioxide nanoparticles (5 nm diameter) marked with the fluorescent dye rhodamine 6G are used as probes. The distributions of diffusion coefficients, obtained by mean squared displacements, reveal heterogeneities with at least two underlying diffusion components. Measurements on films with varying film thicknesses show that the slower component is independent of the film thickness, while the faster one increases with the film thickness. Additionally, we could show that the diffusion behavior of the particles cannot be sufficiently described by only two diffusion coefficients.
The Journal of Chemical Physics, 2010
We apply the recently developed triangular tessellation technique as presented in [J. de Graaf et al., Phys. Rev. E 80, 051405 (2009)] to calculate the free energy associated with the adsorption of anisotropic colloidal particles at a flat interface. From the free-energy landscape, we analyze the adsorption process, using a simplified version of Langevin dynamics. The present result is a first step to understand the time-dependent behavior of colloids near interfaces. This study shows a wide range of adsorption trajectories, where the emphasis lies on a strong dependence of the dynamics on the orientation of the colloid at initial contact with the interface. We believe that the observed orientational dependence in our simple model can be recovered in suitable experimental systems.
Journal of Colloid and Interface Science, 2010
The electric field of charged particles, which are adsorbed at a liquid interface, induces interfacial deformations (capillary menisci). The overlap of such deformations gives rise to electrocapillary force of interaction between the particles. Our goal is to quantify this interaction on the basis of a force approach, which is different from the approaches (mostly based on energy calculations) used by other authors. The fact that the electric field of adsorbed particles has a dipolar asymptotics (due to the image-charge effect) is utilized to derive an analytical expression for the meniscus profile. The comparison of the calculated profile with experimental data indicates that the results based on the dipolar approximation agree excellently with the data, except some small deviations near the contact line. The effect of the interfacial deformation on the electrostatic pressure is also taken into account. The two-particle electrocapillary problem is solved in bipolar coordinates without using the superposition approximation. It turns out that for uniform distribution of the surface charges, the electrocapillary attraction is weaker than the electrostatic repulsion at interparticle distances at which the dipolar approximation is applicable, so that the net force is repulsive. This result is in agreement with the conclusions of other authors obtained by using different theoretical approaches and with available experimental data. The analytical expressions for the electrocapillary and electrodipping forces derived in the present article provide a simple and convenient way for estimation of these forces.
Dynamic Effects on the Mobilization of a Deposited Nanoparticle by a Moving Liquid-Liquid Interface
Physical Review Letters
Using molecular dynamics simulations, we investigate the fate of a nanoparticle deposited on a solid surface as a liquid-liquid interface moves past it, depending on the wetting of the solid by the two liquids and the magnitude of the driving force. Interfacial pinning is observed below a critical value of the driving force. Above the critical driving force for pinning and for large contact angle value we observe stick-slip motion, with intermittent interfacial pinning and particle sliding at the interface. At low contact angles we observe that particle rolling precedes detachment, which indicates the importance of dynamic effects not present in static models. The findings in this work indicate that particle mobilization and removal efficiencies originating in dynamic liquid-liquid interfaces can be significantly underestimated by static models.
DYNAMICS OF PARTICLES ON INTERFACES AND IN THIN LIQUID FILMS
The invention of uniformly sized, polymer micro-spheres in 1950s provided the possibility for a direct optical observation of various equilibrium structures and dynamic processes in two dimensions (2D). These include 2D-phase transitions, particle aggregation, deposition on solid surfaces, fracture of 2D particulate layers, and many others. The initial interest was driven mainly by the possibility for direct observation and precise quantitative analysis of these complex phenomena, which include many-body interactions and are of great interest for the condensed matter physics. The optical observations have been often combined with computer experiments, in which the collective properties of the particles are simulated. During the last decade, the research interest shifted to a large extend towards the mechanisms and procedures for controlled fabrication of new 2D-structured materials, which possess unique optical properties and has a potential for various applications in nanotechnolog...
Physical Review E, 2009
We report an optical and atomic force microscopic ͑AFM͒ study of interactions between weakly charged silica spheres at a water-air interface. Attractive interactions are observed at intermediate interparticle distances and the amplitude of the attraction increases with the amount of salt ͑NaCl͒ added into the water phase. AFM images obtained in the salty water show the formation of patchy charge domains of size ϳ100 nm on the silica surface. The experiment suggests that surface heterogeneity produced during ionization plays an important role in the generation of attractions between like-charged particles at the interface.
Langmuir, 2009
In a previous study, we established that the attraction between electrically charged particles attached to a water/tetradecane interface is stronger than predicted on the basis of the gravity-induced lateral capillary force. Here, our goal is to explain this effect. The investigated particles are hydrophobized glass spheres of radii between 240 and 320 μm. Their weight is large enough to deform the liquid interface. The interfacial deformation is considerably greater for charged particles because of the electrodipping force that pushes the particles toward the water phase. By independent experiments with particles placed between two electrodes, we confirmed the presence of electric charges at the particle/tetradecane interface. The theoretical analysis shows that if the distribution of these surface charges is isotropic, the meniscus produced by the particle electric field decays too fast with distance and cannot explain the experimental observations. However, if the surface-charge distribution is anisotropic, it induces a saddle-shaped deformation in the liquid interface around each particle. This deformation, which is equivalent to a capillary quadrupole, decays relatively slow. Its interference with the gravity-induced isotropic meniscus around the other particle gives rise to a longrange attractive capillary force, F ∼ 1/L 3 (L = interparticle distance). The obtained agreement between the experimental and theoretical curves, and the reasonable values of the parameters determined from the fits, indicate that the observed stronger attraction in the investigated system can be really explained as a hybrid interaction between gravity-induced "capillary charges" and electric-field-induced "capillary quadrupoles".
Wetting and particle adsorption in nanoflows
Physics of Fluids, 2005
Molecular dynamics simulations are used to study the behavior of closely-fitting spherical and ellipsoidal particles moving through a fluid-filled cylinder at nanometer scales. The particle, the cylinder wall and the fluid solvent are all treated as atomic systems, and special attention is given to the effects of varying the wetting properties of the fluid. Although the modification of the solid-fluid interaction leads to significant changes in the microstructure of the fluid, its transport properties are found to be the same as in bulk. Independently of the shape and relative size of the particle, we find two distinct regimes as a function of the degree of wetting, with a sharp transition between them. In the case of a highly-wetting suspending fluid, the particle moves through the cylinder with an average axial velocity in agreement with that obtained from the solution of the continuum Stokes equations. In contrast, in the case of less-wetting fluids, only the early-time motion of the particle is consistent with continuum dynamics. At later times, the particle is eventually adsorbed onto the wall and subsequently executes an intermittent stick-slip motion. We show that van der Walls forces are the dominant contribution to the particle adsorption phenomenon and that depletion forces are weak enough to allow, in the highly-wetting situation, an initially adsorbed particle to spontaneously desorb.