Some New Contributions to the Theory of Polyelectrolyte Solutions: Prediction of Polyion Conformation and Interpretation of Some Deviations from Kohlrausch’s Law According to the Superposition Principle and the Dielectric Friction Effect

M'halla, Jalel; Boughammoura, Sondes; Ghazouani, Anis

doi:10.1007/s10953-019-00916-9

Cited by 5 publications

(1 citation statement)

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“…In "weak" electrolytes, the concentration dependence of the equivalent conductivity is much stronger, due to the incomplete dissociation, which becomes complete only at infinite dilution [36,58]. Polyelectrolyte solutions also do not obey the linear limiting law, which is attributed to the high charge density of the polyions and to the flexibility of the polyion chain and its ability to change conformation [60]. A similar strong concentration dependence is here observed for the electrolyte solutions inside ionomers, including those containing strong sulfonic acids, such as SPEEK (Figure 2) and Nafion [30,34].…”

Section: Discussionmentioning

confidence: 99%

Effective ion mobility in anion exchange ionomers: Relations with hydration, porosity, tortuosity, and percolation

Knauth

Pasquini

Narducci

et al. 2021

Journal of Membrane Science

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The effective mobility of hydroxide, chloride and fluoride ions is reported in various anion exchange membranes (AEM) with a backbone of polysulfone (PSU) or poly(2,6-dimethyl-1,4-phenylene)oxide (PPO). The concentration dependence of the effective mobility is used to derive the porosity (π), tortuosity (τ), and percolation thresholds and to plot the ionic conductivity vs the hydration number. Semi-logarithmic plots of the effective ion mobility u(i) vs the square root of concentration √c(i) for hydroxide, fluoride and chloride ions in various PSU-and PPO-based ionomers at 25 and 60 °C show linear relations, from which the ratio π/τ can be determined. This existence of linear u(i)=f(√c(i)) plots is related to the very particular boundary conditions experienced by mobile ions, migrating in close vicinity to the immobile grafted counter-ions placed at the interfaces between polymer domains and electrolyte solution. The π/τ values for PSU-QA (0.29) and PPO-QA (0.38) are consistent with a relatively low hydrophilic-hydrophobic nanophase separation, which leads to channels with low diameter and high tortuosity. The tortuosity determined from a Bruggeman-type relation is 1.9 for PSU-QA and 1.6 for PPO-QA. The percolation thresholds , determined from the universal percolation equation near and above , are at a water volume fraction of 0.07 for PSU-TMA and 0.03 for PPO-QA indicating that these AEM have a two-dimensional structure of the hydrated domains. The prefactor, which should represent a good indication as to the maximum achievable ionic conductivity, is slightly below 100 mS/cm for both PSU-TMA and PPO-based ionomers. Plots of experimental and computed hydroxide and chloride ion conductivities as function of the hydration number () show a maximum ionic conductivity for a value of the hydration number around 60, corresponding to optimal hydration conditions. At λ = 100, the ratio of conductivity between PSU-QA (OH form) and PPO-QA (Cl form) indicates that the degree of dissociation of ion pairs is about 30% lower for hydroxide than for chloride ions, which is consistent with the effective ionic radii of Cl and OH -.

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