SINGLE COMPONENT NANOCOLLOIDS AND NANOHYBRID MEMBRANES: SYNTHESIS, CHARACTERIZATION AND PROPERTIES
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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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Date Issued
2006-11-29T16:44:16Z
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Keywords
Nanocolloids; Surface Functionalization; Fuel Cells; Ionic conductivity