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Authors: Herrera Alonso, Rafael
Keywords: Nanocolloids
Surface Functionalization
Fuel Cells
Ionic conductivity
Issue Date: 29-Nov-2006
Abstract: Surface functionalized nanoparticles have undoubtedly attracted a great deal of interest in the interdisciplinary fields of nanoscience and nanotechnology. In this thesis two different sets of nano-materials based on surface functionalized nanoparticles are presented. First, single component silicon dioxide nanocolloids (SCN) are nanostructures that exhibit liquid-like behavior in the absence of solvents and preserve the nanostructure in the liquid state. SCNs consist of three main components: a core nanoparticle, a charged oligomer tethered to the core nanoparticle and a canopy that acts as the counter charge to the charged oligomer corona. The individual contribution of the constituents of SCN is studied by surface functionalizing silica nanoparticles with 3- (trihydroxysilyl)-1-propanesulfonic acid, followed by a direct neutralization of the sulfonic protons by a bulky, tertiary poly(ethylene glycol)-tailed amine. By varying the ratio of the constituents, it is established that the suppression of crystalline regions of the canopy is due to confinement effects imposed by the presence of the surface functionalized nanoparticles. It was also found that at temperatures below the melting point of the canopy, the associated molecular motions at short length scales related to the glass transition of the canopy were hindered due to the electrostatic interaction between the canopy and the charged oligomer corona. Finally, the structure of SCNs is characterized by small angle X-ray scattering. Nafion-nanohybrid membranes as proton conducting materials are developed in the second part of this thesis. Nafion membranes are modified with different protonconducting nanoparticles tailored to add proton conductivity and act as barriers to reduce methanol permeability. A preparation method is presented that produces pliant, elastic, and insoluble in water polymer membranes with homogenous distribution of different nanostructures that influence the morphology of the polymer matrix and its transport properties. The resulting materials showed for some cases an 80% reduction of methanol permeability with comparable ionic conductivities than that of Nafion. Characterization of the nanostructure of Nafion nanohybrid membranes is presented in addition to their transport properties proton conductivity and methanol permeability.
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