Effective pair potential between confined charged colloidal particles

Abstract

The pair correlation function g(r) between like-charged colloidal particles in quasi-two-dimensional geometries is measured by optical microscopy for a wide range of particle concentrations and various degrees of confinement. The effective pair potential u(r) is obtained by deconvoluting g(r) via Monte Carlo computer simulations. Our results confirm the existence of a long-range attractive component of u(r) and the appearance of an extra attractive term under stringent confinement.

Like-charge attraction in confinement: myth or truth?

“…Therefore, it was speculated that the confining plates are responsible for the deviations from theory. Soon after its initial observation LCA was also observed by other authors [5][6][7][8][9][10][11] which then provoked considerable theoretical interest in this phenomenon. In the meantime it has been rigorously proven that the observed attraction can not be explained within the framework of mean field theories, irrespective of whether the particles are suspended in bulk or in confinement [12][13][14] .…”

“…The experiments were performed with highly charged silica particles of diameter σ = 1.5 ± 0.08 µm which were confined in thin sample cells. The fabrication of thin cells has been described in detail elsewhere 8 . Briefly, bidisperse suspensions containing the above silica particles and a small amount of slightly larger polystyrene particles (σ = 1.96 µm) were dialyzed against pure water for several weeks to obtain good deionization.…”

Hydrodynamic interactions in quasi-two-dimensional colloidal suspensions

“…This quantity is determined solely by the total direct interparticle interaction, and it is therefore a direct measurement of that interaction [17]. Fig.…”

Bound pairs: Direct evidence for long-range attraction between like-charged colloids

“…Hence, U(r) can be obtained by measuring g(r). Optical microscopy and optical tweezer techniques have been used to measure g(r) by imaging the colloidal particles [12][13][14]. However, only the particles close to the microscope cover-glass could be imaged in these studies because of the limited depth of focus.…”

“…Thus, these studies allow determination of the effective interaction between the colloidal particles under confinement. It must also be mentioned that the attraction observed in the effective pair-potential using optical tweezer technique can be accounted for by a nonequilibrium hydrodynamic effect [14,15]. Thus, to date, there is no direct experimental evidence for existence of a long-range attractive term in the U(r) of likecharged colloids in a bulk (confinement-free) suspension.…”