Ordered structure in dilute solutions of highly charged polymer lattices as studied by microscopy. I. Interparticle distance as a function of latex concentration

Abstract

The coexistence of ordered and disordered regions has been observed in dilute solutions of highly charged monodisperse latex particles, a copolymer of styrene and styrenesulfonate, by using a metallurgical microscope. Unlike latex particles of low charge numbers, the interparticle distances (2Dexp) in the hexagonal ordered regions are smaller than the calculated average values for a face-centered-cubic distribution (2D0,h) at low polymer concentrations (0.2–2 vol %). However, at high concentrations, up to 12%, the 2Dexp value approaches 2D0,h. The results are consistent with a ‘‘two-state structure’’ containing ordered and disordered regions and indicate the existence of ‘‘attractive’’ interactions between the charged solutes. The findings are also consistent with those for other species of high charge densities such as synthetic macroions and simple ions.

Where the linearized Poisson–Boltzmann cell model fails: Spurious phase separation in charged colloidal suspensions

“…(53) is very close to the (largest) salt-free saturation (Z → ∞) effective charge θ sat = 3Z sat ℓ B /a ≈ 45 determined by Alexander et al 24 It has been speculated 15 that this curious coincidence drives suspensions of highly charged colloids close to criticality. This might account for some of the experimental findings in dilute deionized aqueous suspensions of highly charged colloids, 41,42,43 which then would be explained by the presence of strong density fluctuations near the criticality. 15 Another consequence that effective charges are below the saturation value, and therefore also below the linearized critical threshold, is that charge renormalization would stabilize the suspension against phase separation, because the unstable region predicted by linearized theory is unreachable (or at least drastically reduced) when including renormalized effective charges.…”

Gas-liquid phase coexistence in colloidal suspensions?

“…. N), have a radius a, a fixed charge −Ze, and hence a surface charge density σ C = Z/4πa 2 . We assume that the suspension is in osmotic equilibrium with a reservoir of monovalent point charges ±e of total density 2n …”

Charge regulation and ionic screening of patchy surfaces

“…In the homogeneous limit this gives a charge densityỹ for the stripes plus the side strips via Eqs. (13) and (15). The average charge densityȳ on the original stripe follows by assigning the charge density to a smaller surface,ȳ =ỹ(D 1 + 2s)/D 1 .…”

“…Ion-ion correlations, which are ignored in the mean-field-type Poisson-Boltzmann (PB) theory, might be an explanation for these observed attractions in the case of multivalent ions. [8][9][10][11][12][13][14] However, evidence for electrostatic attractions has also been reported for suspensions with only monovalent ions, [15][16][17][18] causing heated debates in the literature on the breakdown of the classic DLVO theory due to many-body effects, the vicinity of glass walls, hydrodynamic forces, etc. Interestingly, it has also been suggested that charge inhomogeneities can be responsible for these attractions, [19][20][21][22][23] where the heterogeneity of the surface charge may be due to an incidentally present or purposely designed underlying chemical structure, or by clustering of adsorbed surfactants.…”