Amorphous nanocomposite of polycarbosilanes and aluminum oxideAndraž Mavrič
, 2018, doctoral dissertation
Abstract: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous.
The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer.
The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm.
The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects.
In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Keywords: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Published in RUNG: 19.07.2018; Views: 5919; Downloads: 210
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FROM SPINODAL DECOMPOSITION AND MOLECULAR DISPERSION OF POLYSILANES TO SUPER-HARD NANOCOATINGArtem Badasyan
, Boštjan Mavrič
, Matjaž Valant
, published scientific conference contribution abstract
Abstract: Conformations of polymer molecules in solution crucially depend on the sign of the
effective potential energy of interaction between the monomers, also known as the
quality of solvent. Therefore in “poor” solvent regime, when effective attraction
overwhelms, the experimental measurements of polymer sizes are complicated by the
agglomeration of macromolecules, followed by precipitation. This phenomenon, also
known as spinodal decomposition, causes serious problems when the goal is to
determine properties of individual macromolecules. Interestingly, while in the case of
carbon-based polymers the precipitation-related problems can be easily avoided with
dilution, this is not the case for polysilanes, i.e. polymeric chains on basis of silicon.
Although the linear polysilanes were first synthesized in early 1920’s, the aggregationrelated
problems have hampered their studies and applicability until recently.
In the Materials Research Laboratory of University of Nova Gorica we have developed
a technology to strengthen the scratch-resistance nanocoating for glass on the basis of
polysilane dendritic polymers we synthesized. Through the prism of the Flory-Huggins
theory, that provides a miscibility phase diagram in temperature-volume fraction
variables, the quality of polymer solution can be manipulated by changing the
temperature. Using Dynamic Light Scattering (DLS) and Differential Scanning
Calorimetry (DSC) we have managed to show, that at temperatures in the range of 40-
50 C the deagglomeration of the dendritic polysilane takes place in tetrahydrofuran
(THF) , and the system becomes a true molecular dispersion with particles 20 nm in
size . Introducing such molecular dispersion into the alumina precursor solution
yields an amorphous nanocomposite stabilized by a high level of strain. This resulted in
an extraordinary increase of hardness and scratch resistance of the alumina – polymer
nanocomposite coating that can be used for glass protection .
Keywords: Polysilane, dendrimer, solubility
Published in RUNG: 12.09.2017; Views: 4212; Downloads: 0
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Molecular dynamics simulations and docking enable to explore the biophysical factors controlling the yields of engineered nanobodiesMiguel Soler
, Ario De Marco
, Sara Fortuna
, 2016, original scientific article
Abstract: Nanobodies (VHHs) have proved to be valuable substitutes of conventional antibodies for molecular
recognition. Their small size represents a precious advantage for rational mutagenesis based on
modelling. Here we address the problem of predicting how Camelidae nanobody sequences can tolerate
mutations by developing a simulation protocol based on all-atom molecular dynamics and wholemolecule
docking. The method was tested on two sets of nanobodies characterized experimentally
for their biophysical features. One set contained point mutations introduced to humanize a wild type
sequence, in the second the CDRs were swapped between single-domain frameworks with Camelidae
and human hallmarks. The method resulted in accurate scoring approaches to predict experimental
yields and enabled to identify the structural modifications induced by mutations. This work is a
promising tool for the in silico development of single-domain antibodies and opens the opportunity to
customize single functional domains of larger macromolecules
Keywords: nanobodies, molecular dynamics, modeling, antibody solubility
Published in RUNG: 11.10.2016; Views: 4551; Downloads: 244
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