On the structure and dynamics of lithium counterions in polyelectrolyte solutions: A nuclear magnetic resonance and neutron scattering study

Abstract

The structure around lithium counterions in polyacrylate solutions has been investigated by neutron diffraction, and it is concluded that small cations remain hydrated when they accumulate around a highly charged polymer. Interactions between the polyion and the counterions over a range outside the hydration shell are also observed. The relaxation rate of 7Li due to dipolar coupling to 17 0 was obtained by nuclear magnetic resonance. The results indicate that the polyion exerts a moderate influence on the reorientational dynamics of the lithium aqua-ion.

Counterion binding in Na poly(acrylate) gel. An 23Na‐NMR study

“…The solvent‐shared ion‐pair formation30 can also cause a downfield shift of the Na + nucleus because the donicity of the intervening water molecules must be enhanced via hydration to the carboxyl anion 21, 26. In fact, many studies suggest that counterion binding of alkali metal poly(acrylate)s in water does not occur via contact ion‐pair formation 31–33. Thus, the observed downfield shift for PAANa and CH 3 COONa systems may be safely ascribed to counterion binding with the solvent‐shared ion‐pair formation mode.…”

X-ray and neutron scattering studies of the hydration structure of alkali ions in concentrated aqueous solutions

“…For example, aqueous solutions of Li-polyacrylate and lithium hydroxide [37] give values for the Li + hydration number of 4.5(5), with similar distances as in lithium chloride. Similarly, an NDIS study of a 4 m LiBr solution also gives a coordination number closer to 4 than those in lithium chloride at similar concentrations [38].…”

Effect of Spatial Inhomogeneity in Dielectric Permittivity on DNA Double Layer Formation

“…This figure should be interpreted as an upper bound, because any lowering of the dielectric constant at a shorter distance scale or inside the grooves escapes detection because TMA ϩ counterions cannot come very close to the DNA surface. It should be noted that small ions remain hydrated when they accumulate around a highly charged polymer, and, except for penetration of the grooves, their spatial distribution is expected to be similar (van der Maarel et al, 1989;Bieze et al, 1994). Any stronger confinement or accumulation of counterions closer to DNA (caused by, e.g., hydrophobic interactions, ion correlation effects, etc.)…”