Electrolyte interactions with colloidal nanoparticles (NPs) in aqueous solutions have been implicated in a wide range of research and applications. Existing studies on electrolyte interactions with NPs are primarily based on the electrical double layer (EDL) theory. However, the EDL model provides very limited information on how electrolytes directly bind to NPs, electrolyte impact on charge distribution on NPs, and NP morphological modification upon electrolyte binding. Furthermore, the previous reports have mainly focused on either cations or anions binding onto NPs, while the potential cation and anion coadsorption onto NPs and NPacilitated cation-anion interactions remain largely uncharted. Filling these knowledge gaps are critical to enhance the fundamental understanding of interfacial interactions of electrolytes with NPs. Experimental characterization of cations and anions at the solid/liquid interface is a challenging analytical task. In the first study, we demonstrated the first direct experimental evidence of ion pairing on gold nanoparticles (AuNPs) in water by using surface enhanced Raman spectroscopy (SERS) in combination with electrolyte washing. Unlike ion pairing in aqueous solutions where the oppositely charged ions are either in direct contact or separated by a solvation shell, the ion pairing on AuNPs refers to cation and anion coadsorption onto the same NP surface regardless of separation distance. Ion pairing reduces the electrolyte threshold concentration in inducing AuNP aggregation and enhances the competitiveness of electrolyte over neutral molecules in binding to AuNPs. In the second study, we demonstrated that binding, structure, and properties of an ionic species on AuNPs are significantly dependent on the counterion adsorbed on AuNPs. These counterion effects include electrolyte-induced AuNP aggregation and fusion, quantitative cation and anion coadsorption on AuNPs, and SERS spectral distortion induced by the ionic species on AuNP surfaces. In the final study, we proposed that ion pairing as the main mechanism for reducing electrostatic repulsion among organothiolates self-assembled on AuNPs in water by using a series of experimental and computational studies. The work described in this dissertation provides a series of new insights into electrolyte interfacial interactions with AuNPs.

<p> Conductivity measurements on liquid hydrogen fluoride solutions of some simple bases and fluoroanion salts were carried out, and a set of equivalent ionic conductivities have been determined. The conductivities of electrolytes in hydrogen fluoride have been compared to those of analogous electrolytes in water and strong acid solvents. A method for the investigation of more complex electrolytes was developed.</p> <p> The mode of ionization of adducts of sulfur tetrafluoride, thionyl tetrafluoride and selenium tetrafluoride with fluoride acceptors in hydrogen fluoride has been investigated by conductivity and nmr spectroscopy. The structures of the solid adducts have also been investigated by Raman spectroscopy. The structure and stability of other sulfur-oxide-fluoride adducts have been investigated and found to differ from adducts of thionyl tetrafluoride. </p> / Thesis / Doctor of Philosophy (PhD)

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Master / Master of Science

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Des simulations de dynamique moléculaire classique prenant en compte explicitement la polarisation ont été réalisées afin de déterminer les propriétés structurales et thermodynamiques de solutions binaires aqueuses de chlorure, perchlorate et nitrate d'uranyle (UO2Cl2, UO2(ClO4)2 et UO2(NO3)2). A partir d'une étude faite en fonction de la concentration en sels, les propriétés d'hydratation et les interactions ion-ion des solutions aqueuses concentrées de chlorure, perchlorate et nitrate d'uranyle ont été étudiées. Les simulations de dynamique moléculaire permettent de reproduire les propriétés de solvatation de l'uranyle, du chlorure, du perchlorate et du nitrate en accord avec les données expérimentales. Les résultats ont montré les différents modes de coordination du chlorure et du perchlorate dans la deuxième sphère de coordination de l'uranyle et la présence de l'anion NO3- dans la première sphère de coordination à concentration élevée.De plus, nous avons calculé les potentiels de force moyenne des paires ioniques à dilution infinite en fonction de la distance et de l'angle. Les propriétés thermodynamiques des solutions ont été calculées à partir des potentiels des paires ioniques en utilisant la théorie McMillan-Mayer et moléculaire. La constante d'association des complexes UO2Cl+ (Kcal =2,52 L mol−1), UO2ClO4+ (Kcal =2,34 L mol−1) et UO2NO3+ (Kcal =3,02 L mol−1) a été calculée et sont en accord avec les données expérimentales. A partir des potentiels effectifs de McMillan-Mayer et en utilisant une approche multi-échelle basée sur l'approximation MSA, nous avons également calculé les coefficients osmotiques. / Classical molecular dynamics simulations with explicit polarization have been successfully used to determine the structural and thermodynamic properties of binary aqueous solutions of uranyl chloride, perchlorate and nitrate (UO2Cl2, UO2(ClO4)2 and UO2(NO3)2). From a study performed as a function of the concentration of salts, the hydration properties of solutes and the ion-ion interactions of concentrated aqueous solutions of uranyl chloride, perchlorate and nitrate have been studied. The molecular dynamics simulations allow for reproducing the solvation properties of the hydrated uranyl, chloride, perchlorate and nitrate in good agreement with the experimental data. The results point out different coordination modes of Cl− and ClO4− in the UO22+ second hydration shell and the presence of NO3− anion in the UO22+ first coordination shell at high concentration. The ion – ion interaction properties over water configurations have been studied at different concentrations.Furthermore, we investigated the potential of mean force of ion pairs at infinite dilution as a function of the distance and the angle. The thermodynamical properties of the solutions have been calculated from these effective ion-ion pair potentials thanks to the McMillan-Mayer theory and molecular theory. The association constant of complex UO2Cl+ (Kcal =2,52 L mol−1), UO2ClO4+ (Kcal =2,34 L mol−1) and UO2NO3+ (Kcal =3,02 L mol−1) has been determined and compared to the experimental ones. From the effective McMillan-Mayer potentials and using a multi-scale approach based on the MSA approximation, we also calculated the osmotic coefficients.

Neste trabalho, apresentamos um estudo por Ressonância Magnética Nuclear (RMN), Análises Termogravimétricas (DSC e TG) e Espectroscopia Infravermelho em cornplexos poliméricos formados entre poli(óxido de etileno), POE, e sais de lítio. Estes complexos tem mostrado uma grande potencialidade em aplicações tecnológicas (baterias, sensores, etc). Desenvolvemos e caracterizamos sensores de umidade e, discutimos como a umidade afeta a conformação do complexo e a mobilidade das espécies iônicas e da cadeia polimérica. Nossos resultados indicam que a hidratação afeta a conformação dos complexos poliméricos através do efeito plasticizante da água, o qual induz uma expansão volumétrica na cadeia do POE. Entretanto, para os níveis de hidratação utilizados, o processo mostrou-se completamente reversível. Através do estudo de RMN, conseguimos diferenciar os movimentos da cadeia polimérica daqueles das espécies iônicas (cátion e ânion). A análise do segundo momento das formas de linha de ressonância e os estudos de relaxação nuclear nos permitiu estimar distâncias médias entre as espécies iônicas e os prótons da cadela nestes complexos. Observamos também, que o comportamento da relaxação spin rede do hidrogênio e do flúor no P(OE)-LiBF4, em função da temperatura e da freqüência, reflete a natureza desordenada do material e a complexidade do processo de condução iônica nestes sistemas / In this work we report on a study using Nuclear Magnetic Resonance (NMR), Thermogravimetry Analysis (TGA), Differential Scanning Calorimetric (DSC) and Infrared Spectroscopy in polymeric complexes formed between poly(ethylene oxide), PEO), and lithium salts. These complexes have shown a large potential in for technological applications in batteries, sensors, etc. We developed and characterized humidity sensors and we discussed how the humidity affects the conformation of the complexes, the mobility of ionic species, and the polymeric chains. The results indicate that the hydration effects the conformation of polymeric complexes by plasticizing the water, which induces a volumetric expansion in the PEO chain. The process was completely reversible for the level of hydration studied. NMR was used to distinguish the movement of polymeric chains from the movement of the ionic species. From the analysis of the second moment of resonance lines and from the study of the nuclear relaxation we were able to estimate the average distance between the ionic species and the proton In the complexes chains. The behavior of spin-lattice relaxation of hydrogen and flurine in the P(EO) LiBF4 as a function of temperature and frequency reflects the nature of the disorder and the complexity of the ionic conduction process In these materials