Pattern formation and Interactions of Like-Charged Colloidal Particles at the Air∕Water Interface (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.
When Like Charges Attract: The Eects of Geometrical Confinement on Long-Range Colloidal Interactions
2000
High-resolution measurements of the interaction potential between pairs of charged colloidal microspheres suspended in water provide stringent tests for theories of colloidal interactions. The screened-Coulomb repulsions we observe for isolated spheres agree quantitatively with predictions of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Confining the same spheres between charged glass walls, however, induces a strong long-range attractive interaction which is not accounted for by the DLVO theory.
Pair interaction of charged colloidal spheres near a charged wall
Physical Review E, 2001
Although equally charged colloidal particles dispersed in clean water are expected to repel each other, an unexplained long-range attraction has consistently been reported for charged colloidal spheres confined by charged macroscopic surfaces. We present an alternative equilibrium measurement of the pair interaction energy for charged spheres near a single charged wall. Analyzing their radial distribution functions for different concentrations reveals a purely repulsive sphere-sphere interaction that is well described by a screened Coulomb potential.
Formation of two-dimensional colloidal voids, soap froths, and clusters
Physical Review E, 1998
We report the observation of new pattern formation by spherical polystyrene particles trapped at the airwater interface; namely, the formation of two-dimensional void, soap-froth, and cluster structures. The formation of the soap-froth structure depends upon the initial surface concentration of particles. The void and soap-froth structures evolve with time. The clusters can be formed after deposition of the sample or as a result of the evolution of the soap-froth structure. The experimental observation can be explained in terms of a balance between electrostatic repulsive and attractive interactions. An optimum cluster size can be obtained from an energy analysis of the system.
Capillary assembly of microscale ellipsoidal, cuboidal, and spherical particles at interfaces
Micron-sized anisotropic particles with homogeneous surface properties at a fluid interface can deform the interface due to their shape. The particles thereby create excess interfacial area and interact in order to minimize this area, which lowers the total interfacial energy. We present a systematic investigation of the interface deformations around single ellipsoidal particles and cuboidal particles with rounded edges in the near field for various contact angles and particle aspect ratios. The correlation of these deformations with capillary bond energies---the interaction energies of two particles at contact---quantifies the relation between the interactions and the near-field deformations. We characterize the interactions using effective power laws and investigate how anisotropic particles self-assemble by capillary forces. Interface deformations and particle interactions for cuboidal particles are weaker compared with those of ellipsoidal particles with the same aspect ratios. For both particle shapes, the bound state in side-by-side orientation is most stable, while the interaction in tip-to-side orientation is repulsive. Furthermore, we find capillary attraction between spherical and ellipsoidal particles. Our calculations therefore suggest cluster formation of spherical and ellipsoidal particles, which elucidates the role of spherical particles as stoppers for the growth of worm-like chains of ellipsoidal particles. The interaction between spherical and ellipsoidal particles might also explain the suppression of the ``coffee-ring effect" that has been observed for evaporating droplets with mixtures of spherical and ellipsoidal particles. In general, our calculations of the near-field interactions complement previous calculations in the far field and help to predict colloidal assembly and rheological properties of particle-laden interfaces.
Like-charge interactions between colloidal particles are asymmetric with respect to sign
Soft Matter, 2009
Two-dimensional dispersions of colloidal particles with a range of surface chemistries and electrostatic potentials are characterized under a series of solution ionic strengths. A combination of optical imaging techniques are employed to monitor both the colloid structure and the electrostatic surface potential of individual particles in situ. We find that like-charge multiparticle interactions can be tuned from exclusively repulsive to long-range attractive by changing the particle surface composition. This behavior is strongly asymmetric with respect to the sign of the surface potential. Collective long-range attractive interactions are only observed among negatively charged particles.
Effect of geometrical confinement on the interaction between charged colloidal suspensions
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1999
The effective interaction between charged colloidal particles confined between two planar like-charged walls is investigated using computer simulations of the primitive model describing asymmetric electrolytes. In detail, we calculate the effective force acting onto a single macroion and onto a macroion pair in the presence of slitlike confinement. For moderate Coulomb coupling, we find that this force is repulsive. Under strong-coupling conditions, however, the sign of the force depends on the distance to the plates and on the interparticle distance. In particular, the particle-plate interaction becomes strongly attractive for small distances which may explain the occurrence of colloidal crystalline layers near the plates observed in recent experiments.
Journal of Colloid and Interface Science, 2013
Particles at a liquid interface Non-densely packed interfacial colloid crystals Particle arrays in external electric field Contact angle Electrodipping force Mehler-Fock integral transform a b s t r a c t Here, we calculate the electric forces acting on uncharged dielectric colloidal particles, which are attached to the interface between a nonpolar fluid (air, oil) and water, in the presence of an applied uniform external electric field directed normal to the interface. The uncharged particle becomes a source of dipolar electric field because it is polarized by the external field. Our goal is to calculate the normal (electrodipping) force acting on each separate particle, and the force of interaction between two identical particles. An exact analytical solution is obtained by solving the Laplace equation in toroidal coordinates and by separating the variables using the Mehler-Fock integral transform. The results show that the dependence of the normal force on particle contact angle is non-monotonic, with a maximum and a minimum. This force can be directed upward or downward depending on the particle contact angle and dielectric constant. An analytical asymptotic expression is derived for the force of interaction between two floating particles in external field. The magnitude of the latter force depends strongly on the particle contact angle a. At a certain value of a, the leading dipolar term becomes zero, and the interaction force is determined by the short-range octupolar term. Then, the attractive lateral capillary forces and van der Waals forces can overcome the electrostatic repulsion and can induce two-dimensional coagulation of the particles at the interface. The effects of the external electric field could find applications for control of the distances between particles in non-densely packed interfacial colloid crystals used in lithographic masks for the production of antireflective coatings, microlens arrays, etc. The case of charged particles in external field is considered in the second part of this study.
Colloidal electrostatic interactions near a conducting surface
Physical Review E, 2007
Like-charged colloidal spheres dispersed in de-ionized water are supposed to repel each other. Instead, artifact-corrected video microscopy measurements reveal an anomalous long-ranged like-charge attraction in the interparticle pair potential when the spheres are confined to a layer by even a single-charged glass surface. These attractions can be masked by electrostatic repulsions at low ionic strengths. Coating the bounding surfaces with a conducting gold layer suppresses the attraction. These observations suggest a possible mechanism for the anomalous confinement-induced attractions.
Le Journal de Physique IV, 2000
The paper summarizes recent theoretical work on the effective interactions between charge-stabilized, spherical colloidal particles. Despite the purely repulsive nature of the effective pair potential, fluid-fluid phase separation is shown to occur at very low salt concentrations, due to a frequently forgotten "volume" term. A longrange attractive component to the pair interaction is predicted when the colloidal particles are confined by charged surfaces (e.g. in slit or pore geometries), in agreement with recent experimental findings. The importance of excluded volume and solvent effects is briefly discussed.