Theoretical and Computational Insight into Solvent and Specific Ion Effects for Polyelectrolytes: The Importance of Local Molecular Interactions

Polyelectrolytes in solution show a broad plethora of interesting effects. In this short review article, we focus on recent theoretical and computational findings regarding specific ion and solvent effects and their impact on the polyelectrolyte behavior. In contrast to standard mean field descriptions, the properties of polyelectrolytes are significantly influenced by crucial interactions with the solvent, co-solvent and ion species. The corresponding experimental and simulation results reveal a significant deviation from theoretical predictions, which also highlights the importance of charge transfer, dispersion and polarization interactions in combination with solvation mechanisms. We discuss recent theoretical and computational findings in addition to novel approaches which help broaden the applicability of simple mean field theories.

Co-nonsolvency of PNiPAM at the transition between solvation mechanisms

For PNiPAM in water–alcohol mixtures addition of alcohol to water suppresses hydrophobic hydration and addition of water to alcohols decreases the solvent quality, which leads to the phenomenon of co-nonsolvency.

Delayed Fatigue of Hydroxy- and Fluorhydroxyapatite Ceramics in Simulated Body Fluid

Ultrafine hydroxyapatite (HA) and fluorhydroxyapatite (FHA) powders were synthesized and dense bioceramic samples were fabricated thereof. The samples were treepoint bend tested in different environments, i.e. in ambient air, distilled water and simulated human saliva, in the wide deformation rate range. Weibull’ statistics test was performed under standard testing conditions but in different media. The stress velocity exponent was evaluated from the dynamic fatigue testing data. The mean strength is shown to decrease when both ceramics are exposed to water or to simulated saliva. HA ceramics is more susceptible to the environment compared to FHA ceramics, due to the later is less subjected to the stress corrosion. Fracture surface observations revealed the crack propagation is of mixed trans- and intergranular mode. Strength distribution changes from uni-modal in air environment to bimodal in harsh conditions of water and saliva, indicating slow increment of flaw size in ceramics. Crack velocity exponent values correspond to transient region from dissociative chemisorption to ion solvation mechanisms of stress corrosion in both HA and FHA ceramics. Generally, FHA ceramics is considered to be much more reliable for application in bone defects replacement or dental reconstruction.

Électrons en excès dans les milieux polaires homogènes et hétérogènes

A review of our present knowledge concerning the solvation of excess electrons e−exc → e−solv produced by photoionization or radiolysis in polar media has been attempted. Various properties of the solvated electron (proposed solvation mechanisms, structure, physicochemical characteristics) are considered. In spite of some similarities, e−solv does not seem to be a good prototype for solvated halide anions. The behavior of e−exc in heterogeneous model systems, such as micellar solutions and molecular clusters, is described and correlated with that observed in homogeneous media. Key words: excess electrons, homogeneous and heterogeneous polar media, photoionization, radiolysis, solvation, charge transfer to solvent, properties of the solvated electron, micellar solutions, molecular clusters, comparison with the solvation of anions.