Measurement of Long-Range Repulsive Forces between Charged Particles at an Oil-Water Interface

Abstract

Using a laser tweezers method, we have determined the long-range repulsive force as a function of separation between two charged, spherical polystyrene particles (2.7 microm diameter) present at a nonpolar oil-water interface. At large separations (6 to 12 microm between particle centers) the force is found to decay with distance to the power -4 and is insensitive to the ionic strength of the aqueous phase. The results are consistent with a model in which the repulsion arises primarily from the presence of a very small residual electric charge at the particle-oil interface. This charge corresponds to a fractional dissociation of the total ionizable (sulfate) groups present at the particle-oil surface of approximately 3 x 10(-4).

Poisson-Boltzmann study of the effective electrostatic interaction between colloids at an electrolyte interface

“…In fact, it is known that for high stability of particle-stabilized emulsions, the contact angle should not deviate strongly from 90 • [21]. In order to keep the present investigation general and in order to be consistent with previous experimental studies [12,13,15], we consider surface charges on both sides of the fluid-fluid-interface. The electrostatic problem for this model system is solved by employing the framework of density functional theory [24] and the resulting effective interaction energy is divided into two parts: a surface contribution, expressed per total surface area, and a line contribution per total length of the two three- (Fig.…”

“…First, we discuss the results for a standard set of parameters (σ std = 0.1, I std = 0.85, ε std = 62/72, b 1 ≈ 0.23, βeΦ D = 1) which corresponds to a typical experimental setup, e.g., a water-lutidine (2,6-dimethylpyridine) mixture with NaI salt (1 mM in the aqueous phase) at temperature T = 313 K in contact with polystyrene walls exhibiting, in the aqueous phase, a surface charge density of 0.1 e/nm 2 [13,25,[27][28][29][30][31]. The resulting interaction energies are presented in Fig.…”

Modifying the liquid/liquid interface: pores, particles and deposition

“…of polystyrene latex) at the interfaces between water and low polarity organic solvents, such as n-octane. 18,123,124 There has been some debate over the physical origin of this long-range order: residual surface charges on the assembled particles, which are un-screened by the low polarity organic solvent, are believed to underlie the observed long-range order. 123 One study highlighted capillary distortion of the interface due to the dipolar field as giving rise to the stable long-range order observed for micron-scale polymer particles at L/L interfaces.…”

“…18 A more recent report has stated that the interparticle force is insensitive to aqueous electrolyte concentration. 124 To the author's knowledge, no studies to date have attempted to assess the validity of the screening theory by assessing the effect of electrolyte added to the organic phase on particle assembly. It could be extremely interesting to introduce the externally applied electric field along with/instead of the surface pressure (normally employed by the colloid scientists) as an extra degree of freedom controlling particle assembly.…”

Effective interactions of colloids on nematic films

“…On one hand, the presence of the interface gives rise to direct dipolar electrostatic repulsions between the colloids (see Refs. [1][2][3] for some experimental evidence), on the other hand deformations of the interface may induce longer-ranged capillary attractions (briefly reviewed in Refs. [4][5][6]) which is possibly the source of pattern formation observed in various experiments [7][8][9][10][11].…”