Capillary Assembly of Microscale Ellipsoidal, Cuboidal, and Spherical Particles at Interfaces (original) (raw)
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Role of Collective Interactions in Self-Assembly of Charged Particles at Liquid Interfaces
The Canadian Journal of Chemical Engineering, 2008
Charged nano-colloidal particles self-assemble and display ordered arrays or other structures at liquid interfaces. We used Monte Carlo (MC) simulations to examine the effect of long-range repulsive collective inter-particle interactions on structural transitions from liquid-like to crystallike. We used the asymptotic pair interaction potential proposed by Hurd (J. Phys. A. Math Gen 18, L1055 (1985)), which includes both the screened Coulombic contribution and the dipole-dipole interaction. The effects of the collective inter-particle interactions on the interfacial 2-D colloid structure formation were quantified by the radial distribution function and the potential of the mean force. The MC simulations agreed with the experimentally observed particle structural transitions at both the air-water and oil-water interfaces. The effects of the particle charge and interfacial coverage on the 2-D structure formation were analyzed. The significance of the results lies in their potential applications in inducing 2-D structural transitions in interfacial colloids to form ordered structures; this controls the emulsion and foam stability, and aids in the fabrication of patterned materials with desirable properties. Les particules nano-colloïdales s'auto-assemblent et montrent des dispositions ordonnées ou d'autres structures aux interfaces liquides. On a eu recours à des simulations de Monte Carlo (MC) pour examiner l'effet des interactions collectives répulsives de longue durée sur les transitions structurelles de la forme de type liquide à la forme de type cristaux. On a utilisé le potentiel d'interaction par paires asymptotiques proposé par Hurd (J. Phys. A. Math Gen 18, L1055 (1985)), qui inclut la contribution de Coulomb et l'interaction dipôle-dipôle. Les effets des interactions interparticulaires collectives sur la formation des structures colloïdales interfaciales en 2-D ont été quantifiés par la fonction de distribution radiale et le potentiel de la force moyenne. Les simulations MC concordent avec les transitions structurelles des particules observées expérimentalement aux interfaces air-eau et huile-eau. Les effets de la charge des particules et de la récupération interfaciale sur la formation des structures en 2-D ont été analysés. La pertinence des résultats repose sur leurs applications potentielles lorsque des transitions structurelles en 2-D sont induites dans les colloïdes interfaciaux pour former des structures ordonnées; ceci permet de contrôler l'émulsion et la stabilité de la mousse et aide à la fabrication de matériaux structurés avec les propriétés souhaitables.
Self-assembly of ellipsoidal particles at fluid-fluid interfaces with an empirical pair potential
Journal of colloid and interface science, 2018
Colloidal particles adsorbed at fluid-fluid interfaces interact via mechanisms that can be specific to the presence of interfaces, for instance, lateral capillary interactions induced by nonspherical particles. Capillary interactions are highly relevant for self-assembly and the formation of surface microstructures, however, these are very challenging to model due to the multibody nature of capillary interactions. This work pursues a direct comparison between our computational modelling approach and experimental results on surface microstructures formed by ellipsoidal particles. We begin by investigating the accuracy of using pairwise interactions to describe the multibody capillary interaction by contrasting exact two- and three-particle interaction energies and we find that the pairwise approximation appears reasonable for the experimentally relevant configurations studied. We then develop an empirical pair potential and use it in Monte-Carlo type simulations to efficiently model ...
Capillary interactions between anisotropic colloidal particles
Physical Review Letters, 2005
We report on the behavior of micron-sized prolate ellipsoids trapped at an oil-water interface. The particles experience strong, anisotropic, and long-ranged attractive capillary interactions which greatly exceed the thermal energy k B T. Depending on surface chemistry, the particles aggregate into open structures or chains. Using video microscopy, we extract the pair interaction potential between ellipsoids and show it exhibits a power law behavior over the length scales probed. Our observations can be explained using recent calculations, if we describe the interfacial ellipsoids as capillary quadrupoles.
Pattern formation and Interactions of Like-Charged Colloidal Particles at the Air∕Water Interface
AIP Conference Proceedings, 2008
In the last decade, there have been experimental reports on the formation of colloidal mesostructures at the air/water interface. These patterns, range from the formation of transient colloidal chains and soap-froth structures that evolve to more energetically stable colloidal clusters. If the surface colloidal density is high, a crystalline-like structure can also be formed. This kind of mesostructures has been observed in particles that range in size from a few nanometers to a few microns. In the case of micron-size charged colloidal particles, the charge asymmetries on the particle's surface at the air/water interface produce the formation of dipoledipole interaction, which should be repulsive. The formation of these mesostructures, where the equilibrium distance among particles is in the micrometer range, has been interpreted as the result of a competition between long-range repulsive and attractive interactions. Measurements of the pair interaction potential in these systems show clear evidence of micron-range attractive interactions between the colloidal particles, whose pattern formation behavior has been reproduced by computer simulations that use such micrometer range attractive interaction. However, a good theoretical understanding on the origin of the attractive component is still missing. Here, we review our main findings on these systems and we discussed them in view of recent results obtained by other groups.
In this supplementary material, we present numerical data to further characterize the interface deformation around and the capillary interaction between ellipsoidal and cuboidal particles. For a contact angle θ c = 90 • , a constant contact angle cannot be achieved for a planar interface around an ellipsoidal particle and around a cuboidal particle with rounded edges. For θ c < 90 • , the interface is pulled down at the tips and pulled up at the sides of the ellipsoids, thereby creating excess interface area. shows the deformation of the interface around an ellipsoidal particle in the directions of the long and the short axis.
Capillary Assembly of Colloids: Interactions on Planar and Curved Interfaces
Annual Review of Condensed Matter Physics
In directed assembly, small building blocks are assembled into an organized structures under the influence of guiding fields. Capillary interactions provide a versatile route for structure formation. Colloids adsorbed on fluid interfaces distort the interface, which creates an associated energy field. When neighboring distortions overlap, colloids interact to minimize interfacial area. Contact line pinning, particle shape and surface chemistry play important roles in structure formation. Interface curvature acts like an external field; particles migrate and assemble in patterns dictated by curvature gradients. We review basic analysis and recent findings in this rapidly evolving literature. Understanding the roles of assembly is essential for tuning the mechanical, physical, and optical properties of the structure.
Capillary-induced interactions between colloids at an interface
Journal of Physics: Condensed Matter, 2005
Within a general framework we study the effective, deformationinduced interaction between two colloids trapped at a fluid interface. As an application, we consider the interface deformation owing to the electrostatic field of charged colloids. The effective interaction is attractive and overcomes the direct electrostatic repulsion at large separations if the system is not mechanically isolated. Otherwise, a net attraction seems possible only for large enough colloidal charges.
Dynamics of colloidal particles with capillary interactions
Physical Review E, 2010
We investigate the dynamics of colloids at a fluid interface driven by attractive capillary interactions. At submillimeter length scales, the capillary attraction is formally analogous to twodimensional gravity. In particular it is a non-integrable interaction and it can be actually relevant for collective phenomena in spite of its weakness at the level of the pair potential. We introduce a mean-field model for the dynamical evolution of the particle number density at the interface. For generic values of the physical parameters the homogeneous distribution is found to be unstable against large-scale clustering driven by the capillary attraction. We also show that for the instability to be observable, the appropriate values for the relevant parameters (colloid radius, surface charge, external electric field, etc.) are experimentally well accessible. Our analysis contributes to current studies of the structure and dynamics of systems governed by long-ranged interactions and points towards their experimental realizations via colloidal suspensions.