Asymptotic structure of charged colloids between two and three dimensions: the influence of salt

Abstract

We present theoretical, computer simulation and experimental results for the structural length scales characterizing bulk and confined charged colloidal suspensions. The target quantities are the bulk pair correlation functions on the one hand, and the oscillatory solvation forces of the colloids in films of various thicknesses on the other. Recently we have shown, for a system with very low salt concentration, that these quantities are characterized by the same wavelength in the asymptotic limit, in agreement with predictions from density functional theory. Here we consider systems with larger ionic strengths of added salt. Our results indicate that the wavelength remains essentially unaffected, whereas the correlation length and the amplitude depend significantly on the amount of added salt. Indeed, already at ionic salt strengths as low as 10 −3 mol l −1 the force oscillations essentially disappear.

Effect of particle size and Debye length on order parameters of colloidal silica suspensions under confinement

“…Previously, we determined that the increase in particle concentration led to an increase in amplitude while the associated increase in counterion concentration led to a decrease in amplitude. 28 The SAXS measurements also showed that, at a given particle concentration, increasing salt concentration caused a reduced intensity (Fig. 8).…”

“…Numerical simulations and density-functional modeling of oscillatory forces on particles entrapped between two planar surfaces were also available. [26][27][28][29] Klapp et al directly compared the structural forces in a CP-AFM experiment for an aqueous suspension of 26 nm diameter silica particles using MC simulations of confinement. A good agreement between simulations and experimental results was achieved: the l f c À1/3 scaling was observed.…”

“…Previous work, including our last three publications, [28][29][30] has experimentally focused on analyzing one key quantity characterizing the oscillatory force: the wavelength. A precise understanding of confinement effect on the full structuring of nanoparticles, namely the oscillatory wavelength and decay length in relation to the bulk counterparts and their relation with the particle size and Debye-H€ uckel length, is however still missing.…”

“…Here, we began the fitting after the first peak of g(r) which yielded better agreement with HNC results than for other fitting ranges used in the previous paper. 28 However, the qualitative behavior of x b , depending on the ionic strength I and the particle concentration, was not affected by the fitting range. The same uncertainty was found using eqn (6) for the correlation length under confinement x f , whereas the wavelength l f yielded good agreement with the experimental results (see Fig.…”

Depletion forces between particles immersed in nanofluids

“…The surface force apparatus (SFA) [62,63] and colloidal-probe AFM (CP-AFM) [52,53] gauge the forces with bending of a calibrated spring. Prominently, micelles [58,[64][65][66][67][68][69] and spherical nanoparticles (particularly SiO 2 [29,52,53,68,[70][71][72]) are among most widely studied model nanofluids for mediating depletion and related structural forces, with nanorods-mediated depletion also measured [60,61].…”