Quantitative determination of cation–π interactions between metal ions and aromatic groups in aqueous media by a hydrogel Donnan potential method

Abstract

The binding ratios of various metal ions to aromatic groups by cation–π interactions in aqueous media have been quantitatively calculated by using Donnan potential measurements.

Origin of Surface Charge of Double Network Hydrogels Prepared by Sequential Polymerization

“…To determine if higher concentrations of C AMPS,R in the second network precursor solution increase the DN hydrogels surface charge density C G after synthesis, we deployed electric potential measurements by using MET. When a polyelectrolyte hydrogel is equilibrated in a salt solution, a characteristic distribution of small mobile ions inside and outside of the gels is created, which generates an electrostatic potential difference (Donnan potential) at the gel−solution interface Δφ: 20,21 i k j j j j j y…”

“…We deployed the microelectrode technique (MET) to precisely quantify the charge concentration at the surface layer of the DN hydrogels. MET measures the Donnan potential of a hydrogel equilibrated in a bath solution through the insertion of an extremely thin capillary electrode into the hydrogel. , …”

“…MET measures the Donnan potential of a hydrogel equilibrated in a bath solution through the insertion of an extremely thin capillary electrode into the hydrogel. 20,21 We synthesized DN hydrogels using PAMPS as the first network and poly(acrylamide) (PAAm) as the second network.…”

“…To determine if higher concentrations of C AMPS,R in the second network precursor solution increase the DN hydrogels surface charge density C G after synthesis, we deployed electric potential measurements by using MET. When a polyelectrolyte hydrogel is equilibrated in a salt solution, a characteristic distribution of small mobile ions inside and outside of the gels is created, which generates an electrostatic potential difference (Donnan potential) at the gel–solution interface Δφ: , normalΔ φ = R T z F nobreak0em0.25em⁣ ln ( γ S × C S γ G × C G ) Here, R is the gas constant, T is the absolute temperature, z is the valence of the small mobile ions, F is the Faraday constant, and γ and C are the activity coefficient and the concentration of the small mobile ion of interest, respectively, in bath solution (γ S , C S ) and in the gel (γ G , C G ). By measuring the Donnan potential of the hydrogel in a low-salt solution, we can estimate the counterion concentration C G in the surface layer of DN hydrogels.…”