Structural analysis of nanoparticles by small angle X-ray scattering

The objective of this work was to analyze nano-scaled particles by the combination of small angle x-ray scattering (SAXS), electron microscopy (TEM and cryo-TEM) and dynamic light scattering (DLS). Two systems with totally di_erent morphologies and compositions have been investigated: spherical particles of calcium-phosphate-protein complexes and hamburgers of semi-crystalline polybutadiene/polyethylene nanoparticles. The study of the calcium-phosphate-protein complexes consisted in looking for the influence of a protein, Fetuin-A, also called ahsg, onto the calci_cation at early stage. For the purpose, calcium and phosphate ions were mixed with or without the presence of Fetuin-A in a buffr solution of pH=7.4. In a first step, DLS measurements were realized to better appreciate the effect of the total weight percentage of Ca2+ and PO43- ions. These experiments, withtout addition of ahsg, demonstrated that for a lower weight fraction, the particles formed are smaller. Studies with addition of Fetuin-A affected the calcification during the first minute of this process. The early formation of calcium phosphate complexes has been successfully followed by TR-SAXS. A very fast nucleation of nanoparticles within 1 second has been detected. For the first time, the role of the glycoprotein Fetuin-A at the very early stage of calcification has been qualitatively highlighted: ahsg inhibits the aggregation of calcium phosphate particles. Thus, Fetuin-A plays an important role in the fetal serum in the pre-formation of the skeleton of Vertebrates. This study demonstrated that a physiological concentration of this glycoprotein (15 µM) is suffcient to completely inhibit the aggregation of calcium phosphate particles. Freely suspended nanoparticles of syndiotactic polybutadiene have been studied. By using the combination of cryo-TEM and SAXS, it has been shown that they consist of remarkably thin polymer crystalline lamella. Different models have been compared in order to theoretically fit the experimental SAXS data: homogeneous and heterogeneous (two and three different electron densities within one particle) nanoparticles. The presence of amorphous and crystalline polybutadiene has been demonstrated by the X-ray diffraction. The necessity of using an additional layer of SDS for the modeling is explained by the abundancy of SDS added after the synthesis of the polybutadiene particles (weight ratio ca. 1:1) and by the modeling of the SAXS theoretical intensities which were not sufficient without taking into account the presence of SDS. After the formation of semi-crystalline nanoparticles of PE, these new nanoparticles open a new route to the synthesis of nanopolymers of interesting physico-chemical properties such as semi-conductors or photovoltaic compounds. Finally, in contrast to recent literature on bulk polyethylene (PE), this thesis investigated freely suspended nanoparticles of PE. As suggested by Weber and coworkers, the combination of SAXS and cryo-TEM has been used for this study. The structure of individual PE nanocrystals has been determined in detail and an improved model of the form factor (SAXS) has been developped in close collaboration with Priv.-Doz. Dr. Ludger Harnau. The second part of this thesis mainly deals with the annealing of these PE particles. For the first time, it is shown that the effect of the annealing process results in a doubling of the crystalline layer of the PE nanoparticles. This behaviour could be traced back to the unlooping of the PE chains. In addition, a linear relationship between the reciprocal of the crystalline layer and the annealing temperature has been experimentally drawn. This line was predicted by the Gibbs-Thomson equation according to the literature. This result is important because it allows controlling the crystalline thickness and physical properties of the system, by the temperature.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2012

Author dc:creator

• Rochette, Christophe N.

Contributors dc:contributor

• Ballauff, Matthias

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/158/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:158