Initiation of aggregation in colloidal particle monolayers

Measuring Inter-Particle Forces at an Interface With Optical Tweezers and a Long Working-Distance Objective Lens

“…Because the water is completely covered, it can be assumed that the ionic concentration of the water is not changing with time. It is possible that the oil is collecting materials from the air which ionize and help shield the repulsion of the particles through the oil phase allowing attractive van der Waals forces to be large enough to pull particles together [37].…”

“…According to Robinson and Earnshaw, the "dipole" that causes the repulsion between the particles is formed by the counterions that are attached to the sulfate groups on the particle in the non-wetted portion, not the attracted counterions from the water [37]. There is "short range repulsive dipole interactions arising from dissociated bound surface groups on the part of the particle" not in the water [37]. Particles manufactured without surfactant make better, more stable crystalline monolayers [37].…”

“…There is "short range repulsive dipole interactions arising from dissociated bound surface groups on the part of the particle" not in the water [37]. Particles manufactured without surfactant make better, more stable crystalline monolayers [37]. The more hydrophobic the particle is, the less screening it experiences in the water phase, and therefore the stronger the repulsion it has on other particles.…”

“…The dipole-dipole interactions dominate at long distances. It has been shown by several researchers that much higher concentrations of salt (100x) are needed to cause agglomeration of particles on an interface compared to a bulk colloid [37]. This implies that the repulsion is much stronger through the other fluid making the interface, be it air or oil.…”

Structural optimization of model colloidal clusters at the air–water interface using genetic algorithms

“…The former will be enhanced since a part of the colloidal particles is exposed in the air and will be attracted to each other by a larger Hamaker constant in the air than in the water. The repulsive dipolar repulsion should be more important [9] than the screened Coulomb repulsion, because the former has a longer range than the latter.…”